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MTD 420 Series Service manual

1. 69 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines Starter Cup The starter cup is a steel cup that is bolted to the flywheel 1 Inspect the inside of the starter cup See Figure 6 2 NOTE If the starter was failing to engage the fly wheel and the edges of the slots inside the cup are burred or damaged replace the starter Cup NOTE If the starter cup is replaced the complete starter should be replaced as well to prevent a repeat failure 2 Block the piston to prevent the crank shaft from turning by Inspect slots 2a Remove the spark plug 2b Insert approximately 3 5 feet of starter rope in the spark plug hole Figure 6 2 NOTE Leave part of the rope sticking out of the engine so that the rope can be removed later 3 Remove the starter cup by removing the flywheel nut 4 Install a starter cup e Place the starter cup on the flywheel with the three bosses on the bottom of the starter cup into the dimples in the flywheel AN ww A Alignment pin ASS ZY Starter cup e Align the pin on the flywheel fan with the hole in the starter cup See Figure 6 3 Alignment hole 5 Install the flywheel nut and tighten it to a torque of 47 52 ft lbs 64 70 Nm Figure 6 3 70 WWwW mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 Starter and Charging System Starter Rope The most common failure mode for most rec
2. e No oil additives or viscosity modifiers are recommended The performance of a good oil meeting the API specifications will not be improved by oil additives NOTE Some oil additives may cause severe and non warrantable engine damage constituting a lubrication failure NOTE If the oil is noticeably thin or smells of gasoline a carburetor repair may be needed before the engine can be run safely NOTE There are two types of dip sticks that can be found on MTD engines a threaded dip stick that was used on older engines and a quarter turn dip stick that is used on engines currently being produced See Figure 1 4 Jf va s T S E 3 z Jen Threaded a E y B 4 x P H VA i SEA Wig E ES e tip zm y Piia 2 z 23a P ed Figure 1 4 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines To check the oil with a threaded dip stick 1 2 Twist and remove the dip stick from the engine Clean the oil off of the tip of the dipstick Re insert the dipstick without threading it in to get the oil level reading See Figure 1 5 The oil level is determined by the lowest point on the dipstick that is completely covered with oil To check the oil with a 1 4 turn dip stick 1 2 3 Twist and remove the dip stick from the engine Clean the oil off of the tip of the dipstick Re insert the dipstick and turn it until it is fully seated to get
3. opening NOTE Soapy water can be used as a lubricant 4 Install the hose from the canister 5 Test run the engine in a safe area before returning to Service Figure 4 19 www mymowerparts com 47 For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines Choke 78 83 90 series MTD engines are equipped with a choke The snow engines are also equipped with a primer both of which must be used to start the engine NOTE The choke should be opened after the engine starts This can be a source of starting issues with cus tomers who are not familiar with manual chokes NOTE On the summer engines the entire choke mechanism is part of the carburetor See Figure 4 20 Figure 4 20 Choke mechanism snow engines The choke is operated by a knob on the engine shroud If the choke plate fails to close fully the engine will be difficult or impossible to start when cold See Figure 4 21 amp Choke knob S amp E Figure 4 21 48 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 FUEL SYSTEM AND GOVERNOR The choke rod is part of the heat box assembly mounted on the front of the carburetor See Figure 4 22 NOTE The choke rod can be bent slightly to facilitate adjustment To adjust the choke rod 1 Remove the choke knob and the engine shroud by following the steps described in Chapter 3 Air Intake Systems 2 Rotate the choke knob
4. Maintenance item Eachuse Each25hrs use Each 50 hrs use Check oil EE NE a gts Check air filter If applicable Note on air filter Dirt may be shaken or tapped out of the air filter but compressed air is not to be used for cleaning Do not wash or oil paper filter element Note on pre filter Foam pre filter may be washed in water and mild detergent and re used Do not oil Check amp gap spark plug Replace if worn EE EE Check cooling fins After prolonged storage Change oil EE EEE EI Note on oil Change oil after first 5 hrs of use and before prolonged storage 14 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 Introduction Frequently used specifications Minimum Maximum in mm in mm Intake valve lash 78 83 90 Exhaust valve lash 0 006 0 15 78 0 008 0 20 83 0 008 0 20 90 0 006 0 15 0 008 0 20 Spark plug gap 78 0 030 0 75 83 0 030 0 75 90 0 026 0 65 0 030 0 75 Module air gap 78 0 024 0 60 83 90 Displacement 78 16 9 cid 277 cc 83 21 8 cid 357 cc 90 25 6 cid 420 cc Governed engine RPM 78 3500 100 83 3500 100 90 3500 100 Oil capacity 78 83 90 Fuel tank capacity 78 83 90 15 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 BASIC TROUBLESHOOTING CHAPTER 2 BASIC TROU
5. PROMO Me ey ey eon ee hae ae ype aes eee rrIT 19 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 Chapter 7 Ignition System Troubleshooting the ignition system 2 0 0 ce ee 81 virer e aos coe coke Cee CeO eames eae eee be tates 82 Remote ignition stop switch snow engines 000 eee 83 Test for ignition that wont turn Off llle 84 AFCO GUNN Cd coos 2 cen dle Be eres nee oe ee eas 2 eee eee 85 MOOUIETEMOVGl au 5 002 2 2 83 13 8 309 3 8 B 9 Be Ped RORN SUR 04 oe 008 Qo ee eee 86 Installing the module and setting the airgap aan 87 EVA E gett ade E areas date ee dane ee eee eee a Enis se ee 88 About the spark plug acer de ic om 2 od er eels de Eee od deuerx Es 89 Cleaning the Spark pli x t utendi iiaae c d D Dee Lowe 89 Inspecti ncorthe Spa DpIBGs o ee kad occa coe be EAR DAD ue Doe eo 89 Sbatk plug FelnoVal 123 5 9 nba exe pP aD CER Ede ERE ER 89 Chapter 8 Exhaust outnimer ehgllies eso gea conet de edt aed ec doe perd c Re bud dod otn 91 Spark arrestor if equipped lllllllelleens 91 Muffler removal replacement 000 eee ee eee 92 Muffler removal replacement snow engineS 00000 eee 94 Chapter 9 Cylinder Head Cylinder head removal timi t Et a 9 Pio ePi ap ao ee reden 97 Cylinder head installation llle 100 Uu P 101 Chapter 10 Crankshaft piston and Connecting Rod Crankshaltinso
6. TINI ILI 4 F7 Ale fel E e im iii ae ie M Aud fo aso nd Comp 0 Mice INSTRUCTIONS FOR VEHICLES WITH NON INTEGRAL COILS Figure 7 10 NOTE If the complaint is that the engine quits running when it gets warm the ignition module should be tested with the engine at normal operating temperature e At operating speed the ignition should produce voltage approaching 12 000 e At pull over speed 600 RPM voltage should be at least 10 000V NOTE The voltage required for a flash over will vary with spark plug condition and gap NOTE Pull over speed may vary from operator to operator NOTE Failure of the magnets in the flywheel is exceedingly rare To test the magnets simply hold an item made of ferrous metal roughly 1 4 0 635cm away from the magnets in the flywheel It should be drawn to the flywheel A wrench or screwdriver is suitable for this test 85 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines Module removal T Unplug the spark plug 2 Remove the engine shroud by following the steps procedures in Chapter 3 Air Intake Systems 3 Remove the front fuel tank shroud using a 10 mm wrench See Figure 7 11 Disconnect the throttle 4 Remove the blower housing switch lead NOTE The recoil starter will come off with the Unhook spark blower housing PUDE D Unhook the spark plug wire from the clip in the car
7. To simply look at synthetic oil and to compare it with Petroleum based oil there is very little difference However when you look at the two through a microscope it is easy to see the difference Syn thetic is made up of smaller molecules This allows the oil to get into areas that petroleum based oil cannot 63 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines Oil dip stick NOTE There are two types of dip sticks that can be found on MTD engines a threaded dip stick that was used on older engines anda quarter turn dip stick that is used on engines currently being produced See Figure 5 1 Threaded Y a Ye Salat ru aa s Tak e us i yt To check the oil with a threaded dip stick 1 Twist and remove the dip stick from the engine 2 Clean the oil off of the tip of the dipstick 3 Re insert the dipstick without threading it in to get the oil level reading See Figure 5 2 4 The oil level is determined by the lowest point on the dipstick that is completely covered with oil Figure 5 2 Fully seat the dip stick To check the oil with a 1 4 turn dip stick 083 before reading it 1 Twist and remove the dip stick from the engine 2 Clean the oil off of the tip of the dipstick Re insert the dipstick and turn it until it is fully seated to get the oil level reading See Figure 5 3 4 The oil level is determined by the lowest point on the dip
8. buretor insulator See Figure 7 12 6 Disconnect the leads that runs from the module to the stop switches See Figure 7 11 T Remove the module using a 10mm wrench Figure 7 12 86 WWwW mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 Ignition System Installing the module and setting the air gap NOTE If just setting the air gap loosen the module mounting screws first then follow the same steps as described below 1 Rotate the flywheel so that the magnets are away from where the module is mounted 2 nstall the module Do not tighten the module down Place a non ferrous feeler gauge between the mod ule and the flywheel NOTE The air gap should be 0 016 0 024 0 4 0 6 mm D f J ae EA 4 Rotate the flywheel so that the magnets align with the gauge 4 B N i Fg legs of the module while holding the feeler gauge in place See Figure 7 13 YO bs Figure 7 13 B 5 Tighten the module mounting screws to a torque of 80 106 in Ibs 9 12 Nm Rotate the flywheel to remove the feeler gauge 6 T Install the blower housing and starter 8 Hook the spark plug wire from the clip in the carburetor insulator 9 Install the Heat box and intake elbow by following the steps described in Chapter 3 Air Intake Systems 10 Connect the spark plug wire to the spark plug 11 Test run the engine before returning to service 87 www mymowerparts com For Parts Call 6
9. 006 0 15 Exhaust valve lash 78 0 008 0 20 83 0 008 0 20 90 0 006 0 15 0 008 0 20 Spark plug gap 78 0 030 0 75 83 90 Module air gap 78 0 60 83 0 60 90 0 60 Displacement 78 16 9 cid 277 cc 83 21 8 cid 357 cc 90 25 6 cid 420 cc Governed engine RPM 78 3500 100 83 3500 100 90 3500 100 Oil capacity 78 83 90 Fuel tank capacity 78 83 90 118 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 Crankshaft piston and connecting rod Engine torque values chart Flywheel nut 0 Flywheel nut 0 66 81 66 81 ft os 90 110Nm lbs 90 110Nm 66 81 66 81 ft os 90 110Nm lbs 90 110Nm 66 81 66 81 ft lbs 90 110Nm lbs 90 110Nm 52 59 Nm 52 55 Nm 52 DO Nm 22 25 Nm 22 25 Nm 22 25 Nm 119 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines 120 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 Failure Analysis CHAPTER 11 FAILURE ANALYSIS A properly maintained engine will provide years of service Occasionally an engine will fail An important part of working on engines is finding out why they failed Was it something the customer did Was it a manufacturing defect Did the engine just wear out All of these questions need to be answered when a failed engine is found Engines can fail in a variety of ways but most failures can be classified in the following categories
10. 24 5 The primer is held to the shroud by a pair of split barbed posts Squeeze the posts to release the barbs See Figure 4 24 NOTE The primer bulb and hose will slide out as an assembly 6 Install the new primer by following the above steps in reverse order Figure 4 24 50 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 FUEL SYSTEM AND GOVERNOR Carburetors If diagnosis indicates a fuel problem inspect the carburetor This is important even if problems are identified elsewhere in the fuel system IMPORTANT the fuel must be tested for alcohol content before diagnosing anything else on the engine NOTE It is important to perform a compression or leak down test before condemning a carburetor An engine can have a borderline compression reading and not create enough of a vacuum to draw in a sufficient fuel air charge NOTE To determine if border line compression is the problem remove the spark plug Squirt a little bit of oil into the combustion chamber to seal the rings Reinstall the spark plug If the engine starts and runs ok then that was the problem If it does not start move on to the carburetor Inspecting the carburetor 1 Remove the float bowl and check for dirt and or varnish 2 Inspect the needle valve and needle valve seat for dirt and or damage 3 Inspect the gaskets and O rings for damage 4 Inspect the vents and orifices verify that they are free of debris NOTE If a
11. B Rope jerks back C Rope will not pull at all e Crankshaft turns no start e Starts runs poorly A Starts then dies B Runs with low power output C Makes unusual smoke when running l Black smoke usually heavy Il White smoke usually heavy Ill Blue smoke usually light D Makes unusual sounds when running l Knock Il Click Il Chirp 17 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines IV Unusual exhaust tone There are tools that the technician can use in order to define the problem such as 1 Interview the customer 1a Get a good description of their complaint 1b If itis an intermittent problem verify what conditions aggravate the problem as best as possible 1c Get an accurate service history of the equipment 1d Find out how the customer uses and stores the equipment Direct observation 2a Donot automatically accept that the customer is correct with their description of the problem Try to duplicate the problem 2b Check the general condition of the equipment visually l Cleanliness of the equipment will indicate the level of care the equipment has received Il Make sure the engine and attachments are securely fastened Il The tune up factors NOTE Most hard starting and poor running conditions can be solved by performing a tune up a Check the condition and amount of oil in the crankcase b Check the level and condition of the fue
12. I9 Remove the crank case cover bolts using a 12mm wrench d Carefully slide the crank case cover off of the crank shaft L Align the timing marks to allow easier removal of the cam shaft and to help protect the compression relief from damage See Figure 10 1 ne a ES Figure 10 1 105 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines Remove the 12 Remove the camshaft balance shaft 13 Remove the balance shaft See Figure 10 2 NOTE The valve tappet should be kept riding against their original lobes Once broken in switching the tappets to run on different cam lobes will cause rapid tappet and cam wear 14 Remove the valve tappets See Figure 10 3 15 Remove the connecting rod cap using a 10mm wrench See Figure 10 4 NOTE Rotating the crank shaft after the connecting rod bolts are removed will help to separate the connecting rod from the cap Remove the connecting rod bolts Figure 10 4 106 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 Remove one of the piston pin retainers Figure 10 5 Piston ring pliers Figure 10 6 Crankshaft piston and connecting rod 16 Push the piston out of the cylinder NOTE Sometimes a ridge of carbon builds up where the cylinder meets the head If this happens the piston can be removed from inside of the cylinder block 17 Remove
13. NOTE Is used to point out information that is relevant to the procedure but does not fit as a step in the proce dure e Bullet points indicate sub steps or points Caution is used to point out potential danger to the technician operator bystanders or sur rounding property Warning indicates a potentially hazardous situation that if not avoided could result in death or serious injury EN Danger indicates an imminently hazardous situation that if not avoided will result in death or CISA serious injury This signal word is to be limited to the most extreme situations 1 Numbered steps indicate specific things that should be done and the order in which they should be done 1a Substeps will be lettered and nested within steps Two or more substeps may be combined to describe the actions required to complete a step Disclaimer This manual is intended for use by trained professional technicians e Common sense in operation and safety is assumed e Inno event shall MTD be liable for poor text interpretation or poor execution of the procedures described in the text e If the person using this manual is uncomfortable with any procedures they encounter they should seek the help of a qualified technician or MTD Technical Support Safety This Service Manual is meant to be used along with the Operator s Manual Read the Operator s Manual and familiarize yourself with the safety and operational instructions for the equipment
14. a hot deposit in the cylinder As the fuel air mixture is drawn into the cylinder it is ignited This creates pressure that tries to push the piston down against the direction of rotation of the crankshaft The sounds and damage created by this is the same as detonation 127 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines 128 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 MTD Products Inc Product Training and Education Department FORM NUMBER 769 04951A 10 2010 www mymowerparts com
15. and gas together and seeing were the boundary layer is See Figure 4 2 The test kit should come with a chart to compare the boundary layer height to alcohol percentage Figure 4 2 38 WWwW mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 FUEL SYSTEM AND GOVERNOR Fuel tank vent The fuel tank vent performs the important task of allowing air into the fuel tank As fuel is being used by the engine the fuel level in the tank drops The dropping fuel level then creates a vacuum in the tank If the fuel tank could not draw air through the vent the vacuum would prevent the fuel from getting to the carburetor The vent is located in the fuel cap See Figure 4 3 od Figure 4 3 NOTE All summer engines built on or after January 1 2011 will have an evaporative emissions EVAP sys tem that the fuel tank vents through not the fuel cap Refer to the evaporative emissions section of this chapter to understand how this system works and how to test it To test the cap vent 1 Remove the fuel cap 2 Clean off the vent 3 Blow air into the vent hole The air should blow throw the vent with little back pressure 4 ouck air through the vent hole Air should freely enter through the vent e Replace the cap if the vent builds pressure or restricts air movement e Acap that maintains pressure will cause the engine to run rich as the fuel in the tank heats and expands forcing it s way past the float valve in the carbu
16. axis of movement As an extra feature the 483 and 490 series engines come with a balance shaft The balance shaft further reduces side to side shaking forces by having an eccentric weight attached to it The shaft is geared to the crankshaft and rotates at the same speed as the crankshaft but in the opposite direction The eccentric weight helps counter act the shaking forces as well as dynamically balances the crankshaft See Figure 10 18 NOTE The timing of the balance shaft to the crank shaft will be covered in the Reassembly sec tion of this chapter Balance shaft Figure 10 18 112 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 Crankshaft piston and connecting rod Reassembly 1 Install the governor shaft NOTE The governor shaft MUST be installed before the crankshaft is installed 2 Clean the cylinder 2a Remove all gasket material from all mating surfaces 2b Clean the cylinder and crank case cover 3 Oil seals 3a Install a new oil seal in the cylinder block 3b Install a new seal in the crank case cover 4 Insert the crankshaft and bearing into the cylinder block NOTE Pre lube the crankshaft with clean 10W 30 motor oil NOTE Use an old piece of microfiche or a seal protector to protect the oil seal lip while inserting the crank shaft 5 Install the piston by NOTE If the piston and connecting rod were separated reconnect them so that the arrow on the piston head points to
17. being worked on Keep a copy of the Operator s Manual for quick reference Operator s manuals may be viewed for free at the brand support website It will be necessary to have the complete model and serial number for the equipment www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines Be prepared in case of emergency Keep a fire extinguisher nearby Keep a first aid kit nearby Keep emergency contact numbers handy Replace any missing or damaged safety labels on shop equipment Replace any missing or damaged safety labels on equipment being serviced Grooming and attire Do not wear loose fitting clothing that may become entangled in equipment Long hair should be secured to prevent entanglement in equipment Jewelry is best removed Protective gear includes but is not limited to Clear eye protection while working around any machinery Protective gloves where necessary Armored footwear when working around any machinery Hearing protection in noisy environments Chemically resistant gloves when working with chemicals or solvents Respirator when working with chemical or solvents Appropriate tinted eye protection when cutting or welding Flame resistant headgear jacket chaps when cutting or welding Remember that some hazards have a cumulative effect A single exposure may cause little or no harm but continual or repeated exposure may Cause very serious harm Clean spills and fi
18. different and there is an orientation to the insulator e The bowl vent channel in the insulator faces the carburetor with the exit toward the bottom e There is a small hole in the insulator to carbure tor gasket The hole should be aligned to allow passage of air through the bowl vent channel to the throttle side bowl vent in the carburetor body 9 Install the insulator and carburetor by following the above steps in reverse order NOTE Tighten the carburetor mounting nuts to a Figure 3 16 torque of 80 106 in Ibs 9 12 Nm 10 Testrun the engine before returning to service 36 WWwW mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 FUEL SYSTEM AND GOVERNOR CHAPTER 4 THE FUEL SYSTEM AND GOVERNOR The function of the fuel system is to store fuel mix the fuel with air in the correct ratio and deliver it to the intake port The fuel system consists of the following components Fuel tank Fuel lines Fuel filter Carburetor NOTE When working on the fuel systems look at the whole system A problem will rarely be isolated to one component Inspecting the fuel NOTE Fuel is the maintenance item most often overlooked by consumers A lot of fuel systems problems are caused by gas that is out of date or fuel with too much alcohol in it When inspecting the fuel Look for water Look for dirt Look for discoloration Sniff carefully to see if it smells like varnish or kerosene save the fuel to sh
19. e Abrasive ingestion e Insufficient lubrication e Over heating e Over speed e Mechanical breakage wear NOTE There may be a combination of failures Finding the cause of an engine failure requires the complete disassembly of an engine and careful examination of the parts With a good understanding of how the engine works close examination of the parts and experience an understanding of why the engine failed can be reached Abrasive Ingestion Abrasive Ingestion is when hard particles are introduced into the engine Particles can be introduced into the engine by leaks in the air intake system through a dirty oil fill plug or by particles of metal that wore off of a part especially during the break in cycle Particles may also be introduced through worn or improperly installed seals or gaskets Some of the engines in this series are designed to be used on snow blowers so they are not equipped with an air filter When used for snow blowing there Is very little risk of dirt ingestion from the intake air because there is no dust in the air when it is snowing NOTE Abrasive ingestion from the intake system generally is from using the equipment in a way that it was not designed for such as blowing hay or cleaning chicken coops These failures are not covered under warranty 1 Abrasive particles that enter the engine through the intake system can be sand hay or dirt See Figure 11 1 2 An abrasive particle that enter the engine usuall
20. lead going to the stop switch Connect the other lead of the digital multimeter to a good ground Set the multimeter to the ohms Q scale Operate the throttle lever while watching the multim eter When the throttle is all the way to the right stop the multimeter should read at or near 0 00 indicat ing continuity See Figure 7 3 e When the throttle is all the way to the left full throt tle the multimeter should not show continuity See Figure 7 4 I A f _no continuity Sam Figure 7 4 82 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 Ignition System Remote ignition stop switch Snow engines To test the remote stop switch 1 Remove the engine shroud by following the proce dures described in Chapter 3 Air Intake System L 2 Disconnect the two wires from the remote switch See Figure 7 5 Remote switch Figure 7 5 3 Connect a digital multimeter to the two tabs on the back of the remote switch 4 Set the multimeter to the ohms scale With the key fully inserted the multimeter should not show continuity See Figure 7 6 With the key removed the meter should show con tinuity See Figure 7 7 5 Ifthe test results do not match the results described in step 4 replace the remote switch p am i Y my Figure 7 7 83 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizo
21. little cleaning and new gaskets will fix the carburetor do it If the carburetor requires extensive cleaning it is better to replace the carburetor IMPORTANT Never try to mechanically clean orifices That will damage them and ruin the carburetor NOTE The jet markings if present may be used for identification purposes but the technician should not attempt to infer orifice sizes from the identification numbers NOTE Installing the wrong main jet or a carburetor with the wrong main jet will produce performance and emissions issues 51 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines Disassembly and rebuilding of the carburetor 1 Clamp off the fuel line to prevent fuel spillage then disconnect the fuel line from the carburetor Disconnect the primer hose Remove the carburetor by following the steps described in Chapter 3 Air Intake and Filter NOTE An insulator separates the carburetor from the cylinder head e A bowl vent port is in a recessed passage on the end of the carburetor that faces the insulator e A second passage in the insulator supplements the passage on the carburetor e Gaskets separate the insulator from the cylinder head and the carburetor from the insulator e A port in the carburetor to insulator gasket ties the bowl vent passages together Check the vent passages See Figure 4 25 Check the gaskets and the insulator block Remove the bowl bol
22. mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines Air filter Summer engines Generally air filters come in two different types a pleated paper element or foam A combination of the two are used on the MTD engine See Figure 1 3 1 Paper pleated element The main function of the air filter is to trap air borne particles before they enter the engine Dirt ingestion can cause serious internal engine damage NOTE Snow engines do not have air filters because the snow will plug up the filter Gen erally the air is clean enough that there is minimal risk of dirt ingestion when the Foam pre filter ground is covered with snow Air filters used on the MTD engine are designed to prevent particles larger than 3 5 micron from pass ing through into the engine E The filter should be checked on a regular basis pos Figure 1 3 sibly several times in a season Typically an air filter should be changed before every season If a foam air pre cleaner is dirty but not in bad of condition it can be cleaned and reused The paper pleated fil ters can be shaken or lightly tapped to free the debris from the filter NOTE Never use compressed air on a paper air filter Compressed air will remove the tiny fibers that are used to catch the dirt in the air Without these fibers the filter is useless Foam pre filters can be washed in warm soapy water NOTE When drying a foam
23. of the metering plug Air drawn from the emulsion air port is metered by the size of the brass orifice at the entrance to the port The fuel and air that feed the pilot and transition Air passage E Fuel metering orifice ports are mixed at the metering plug he metering plug creates a small venturi The pressure drop of the air passing through the meter i ing plug draws the fuel into the passage to the pilot Figure 4 33 and transition ports in an emulsified mixture E Transition ports Pilot port Sau NOTE The pilot screw regulates how much of this pre Pilot screw mixed fuel air emulsion is allowed to enter the before head throat of the carburetor to atomize down stream of As removed the throttle plate On current production units it is set at the factory and the screw head is removed See Figure 4 34 NOTE The transition ports are fixed They are drilled into the throat of the carburetor down stream of the venturi They lie behind the brass welch plug near the pilot screw 13 Soak the Carburetor body in a suitable solvent until clean NOTE Ultrasonic cleaning using a suitable water deter Figure 4 34 gent mixture will clean carburetors safely and effectively Adjustment screw 14 Rinse it thoroughly 15 Dry the carburetor body using compressed air 16 Reassemble the carburetor and install it by following steps 1 8 in reverse order 17 Start the engine and check the idle RPM using a tach
24. pressed all the way down on the governor gear flyweights Pushing on the gov ernor arm to the right ensures the throttle is wide open against the throttle stop Re tighten the governor arm nut to crimp the governor arm onto the governor shaft Install the fuel tank 8 Test run the engine in a safe area Set the engine RPM s to 3500 100 61 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 Lubrication CHAPTER 5 LUBRICATION Oil type and quantity MTD engines use oil with a SF SG API rating or better is the recommended oil for this engine e The winter engines use SAE 5W 30 oil e The summer engines use SAE 10W 30 oil e The oil capacity for all of the 78 83 90 series engines is 37 fl oz 1 1 liters 4 F 14 F 32 F 50 F 68 F 86F 104F 20 C 10 C OC 10 C 20 C 30 C 40 C Oil Chart e ftheoil is noticeably thin or smells of gasoline a carburetor repair may be needed before the engine can be run safely e Check the oil level frequently and change the oil more frequently in severe operating conditions such as exceptionally deep snow falls e Synthetic oil is a suitable alternative but it does not extend service intervals NOTE MTD recommends the use of petroleum oil during the break in period to ensure the piston rings cor rectly break in oynthetic vs Petroleum based oil
25. replacement Snow engines To remove replace the muffler 1 Remove the control panel by following the proce dures described in Chapter 3 Air Intake System 2 Remove the muffler heat shield by 2a Remove the two rear heat shield screws using a 10 mm wrench See Figure 8 7 l C r OQ V e nese oe l EO Figure 8 7 3 Remove the screw that holds the heat shield to the cylinder head using a 10 mm wrench See Figure 8 8 4 Work the heat shield off of the engine Remove the three screws that secure the exhaust pipe shield using a 10 mm wrench See Figure 8 9 Figure 8 9 94 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 Exhaust 6 Remove the two muffler nuts using a 13mm wrench and lift the muffler off of the engine See Figure 8 10 7 Clean all of the gasket material off of the cylinder head and the muffler if reusing the muffler NOTE The MTD engine uses a graphite exhaust gasket It is not reusable and must be replaced every time the muffler nuts are loosened Install a new gasket Install the muffler and tighten the muffler nuts to a torque of 13 16 ft lbs 18 22 Nm 10 Test run the engine before returning to service Figure 8 10 95 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines 96 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 Cylinder head CHAPTER 9 CYLINDER HEA
26. side should be 0 004 0 006 0 10 0 15mm See Figure 1 14 Exhaust valve lash muffler side should be 0 006 0 008 0 15 0 20mm See Figure 1 15 Use a 10mm wrench to loosen the jam nut and a 14mm wrench to adjust the rocker arm fulcrum nut See Figure 1 15 e Tighten the rocker arm fulcrum nut to close up the clearance between the end of the valve stem and the contact point on the rocker arm Loosen the rocker arm fulcrum nut to open up the clearance between the end of the valve stem and the contact point on the rocker arm Hold the fulcrum nut with a 14mm wrench tighten the jam nut to a torque of 80 106 in Ib 9 12 Nm using a 10mm wrench Probe to confirm piston is at top of travel T push rods A Push rods iy relaxed CS Valves closed ack M Sel f 5 Si Lis a wp WOES UN gauge 008 feeler gauge Yi T Figure 1 14 Figure 1 15 www mymowerparts com 13 For Parts Call 606 678 9623 or 606 561 4983 Introduction Double check the clearance after tightening the jam nut to confirm that it did not shift Re adjust if necessary Rotate the engine through several compression cycles e Observe the movement of the valve gear e Return the piston to TDC compression stroke and re check the valve lash to confirm consistent movement of the valve gear including the slight bump to the exhaust valve from the automatic compression release Clean up any oil a
27. the oil hole in the connecting rod See Figure 10 19 5a Compress the piston rings using a piston ring compressor 5b Pre lube the cylinder wall with clean 10W 30 motor oil 5c Slide the connecting rod and piston into the cyl inder Figure 10 19 NOTE The arrow on the piston must point towards the push rod cavity e p od Tap the piston through the ring compressor into p the cylinder using a wooden hammer handle See Figure 10 20 NOTE Make sure the crank pin is at BDC bottom dead center to prevent damage from the connecting rod gt EU th 5e Pre lube the connecting rod with clean 10W 30 EN v Tappiston with motor oil P ae hammer handle 5f Install the connecting rod cap Tighten the cap Pad uM a bolts to a torque of 106 124 in Ibs 12 14Nm Figure 10 20 113 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines 10 11 12 13 14 15 16 17 18 19 20 21 22 114 Install the balance shaft by 6a Pre lube the balance shaft with clean 10W 30 motor oil 6b Rotate the crankshaft until the timing mark on the larger gear points to the 7 30 position 6c Insert the balance shaft while aligning the tim ing marks See Figure 10 21 Install the valve tappets Install the cam shaft by 8a Pre lube the cam shaft with clean 10W 30 motor oil 8b Rotate the crank shaft until the timin
28. the oil level reading See Figure 1 6 The oil level is determined by the lowest point on the dipstick that is completely covered with oil Changing the oil NOTE If the engine has been running allow the engine to cool before doing any mainte nance work Figure 1 5 NOTE The oil should be changed after the first 5 hours of operation and every 50 hours there after Place a suitable drain pan under the drain plug to collect the oil Drain the oil by removing the drain plug located at the end of the extension pipe threaded into the base of the engine using a 10mm wrench See Figure 1 7 When all of the oil has drained out reinstall the drain plug Tighten the drain plug to a torque of 106 124 in lbs 12 14 Nm Fill the engine with 37 fl oz 1 1 liters of fresh clean oil that is the appropriate weight for the application Safely dispose of the used oil according to the local laws and regulations Figure 1 7 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 Introduction Fuel Gasolines currently on the market are not pure gasoline Today s fuels have alcohol and other additives in them to reduce emissions The fuel make up can vary seasonally and geographically Fuel with alcohol added to it is sometimes referred to as oxygenated fuel The extra oxygen carried by the etha nol increases the oxidation of the fuel This speeds up the process that causes the fuel to go bad
29. 0 H etched on the top surface of the middle piston ring 1 rea s Figure 10 10 109 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines 7 Measure the gap between the ring and the ring land L using a feeler gauge and compare the measure ment to the chart at the end of this chapter See Figure 10 11 4 e A Y Figure 10 11 8 Measure the piston pin bore on both sides of the piston using telescoping gauges or vernier caliper See Figure 10 12 NOTE Measurements should be taken at right angles to check the roundness of the holes Piston pin bore Figure 10 12 Eu 4s 9 Measure the piston pin at the center and the ends m using a micrometer or a vernier caliper E ow See Figure 10 13 Li L4 e n Figure 10 13 110 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 Crankshaft piston and connecting rod Connecting rod inspection Measure at 7 l right angles 1 Inspect the connecting rod for cracks or any signs of Paley damage T ti i Rete Dr 2 Install the rod cap and tighten to a torque of 106 124 in lbs 12 14Nm 3 Measure the inside diameter of the connecting rod at both ends and compare the measurements to those listed in the chart at the end of this chapter See Figure 10 14 NOTE Take two measurements 90 degrees apart This will check the roundness of the connectin
30. 06 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines Flywheel The flywheel holds the magnets These magnets induce a field in the module which in turn produces a spark It also controls the timing of the ignition system by controlling when the magnets are introduced to the module A sheared flywheel key will throw off the ignition timing Sheared keys are uncommon on MTD engines If one is found check the crankshaft and flywheel for damage To Remove and or inspect the flywheel and key 1 Remove the blower housing 1a Remove the engine shroud by following the steps procedures in Chapter 3 Air Intake Systems 1b Remove the front fuel tank shroud using a 10 mm wrench 1c Remove the five screws securing the blower housing and slide it off of the engine 2 Block the piston to prevent the crank shaft from turning by 2a Remove the spark plug 2b Insert approximately 3 5 feet of starter rope in the spark plug hole IMPORTANT Leave part of the rope sticking out of the engine so that the rope can be removed later 3 Remove the flywheel nut starter cup and flywheel fan using a 23mm wrench 4 Remove the flywheel by applying a sharp blow to the crankshaft using a brass drift punch and a ham mer while gently prying with a pry bar The flywheel will loosen then lift it off NOTE The magnets on the inside of the magnet will hold it down preventing the typical pop when the flywheel loosens from the tapper on the cra
31. 4 Remove the air filter assembly Figure 3 5 30 WWwW mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 AIR INTAKE SYSTEMS 5 Install the air filter by following the previous steps in reverse order NOTE When installing the air filter the hole in the bottom of the paper element must fit over the riser in the air filler base See Figure 3 6 Figure 3 6 31 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines Air filter base and control panel Summer engines To remove replace the air filter base and control panel 1 Remove the air filter following the steps described in the previous section 2 Remove the three screws that hold the air filter base to the intake elbow See Figure 3 7 Pull off the throttle lever knob See Figure 3 8 Remove the two carburetor nuts using a 10 mm wrench D Remove the bolt from the front of the control panel using a 10 mm wrench 6 Align the throttle lever choke lever and the fuel shut off lever in the middle of their slots 7 Remove the bolt that holds the rear of the control panel to the throttle bracket See Figure 3 9 8 Disconnect the breather hose 32 m n Air filter base Screws Figure 3 7 A Ah Throttle lever Control E E panel Choke lever Carb i SS Throttle bracket Figure 3 9 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4
32. 4 14 NOTE If the roll over valve does not hold a vacuum the hose has blocked Replace the hose 45 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines Charcoal canister To remove replace the charcoal canister 1 Disconnect the hoses from the canister See Figure 4 15 2 Remove the screw from the canister mounting strap using a 10 mm wrench See Figure 4 16 To Install the canister 3 Insert the tab of the mounting strap into the slot in the fuel tank mounting bracket See Figure 4 17 4 Install the mounting screw Attach the hoses 6 Test run the engine in a safe area before returning to service Figure 4 17 46 www mymowerparts com FUEL SYSTEM AND GOVERNOR For Parts Call 606 678 9623 or 606 561 4983 Roll over valve A To remove the roll over valve 1 Gently pry the grommet from in between the roll over valve and the fuel tank See Figure 4 18 NOTE Leaving the hose connected to the roll over valve will help prevent it from falling inside the tank once the grommet is removed 2 Lift the valve out of the fuel tank 3 Disconnect the hose tte AEI an S8 Jguia jams J j i ADE UNS T a pan Man ipsu fu ES Cu zd To install the roll over valve Inspect the rubber grommet replace if damaged 1 Slide the rubber grommet over the roll over valve Press the roll over valve assembly into the fuel tank 3
33. 983 AIR INTAKE SYSTEMS NOTE All summer engines built on or after January 1 2011 will have a hose from the evaporative emis sions EVAP system attached to the control panel above the breather hose See Figure 3 10 i EL za p Wwe 1 Ai 3 eee 9 Pull the control panel straight off the front of the engine 10 Install the control panel by following the previous steps in reverse order NOTE tighten the carburetor nuts to a torque of 80 106 in lbs 9 12 Nm 11 Test run the engine before returning it to service ri Figure 3 10 33 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines Carburetor and Insulator 1 Siphon the fuel out of the fuel tank To avoid personal injury or prop erty damage use extreme care in handling gasoline Gasoline is extremely flammable and the vapors are explo sive Keep away from sources of ignition Serious personal injury can occur when gaso line is spilled on yourself and or your clothes which can ignite Wash your skin and change clothes immediately NOTE Dispose of drained fuel in a safe and responsible manner 2 Remove the fuel tank front bezel using a 10 mm a wrench See Figure 3 11 Figure 3 11 NOTE The bezel may get stuck on the cup for the recoil starter If it does the recoil starter is easily removed with an 8 mm wrench 3 Disconnect the fuel line from the fuel tank S
34. BLESHOOTING Definitions Troubleshooting The act of gathering information by preforming tests and direct observations Diagnosis Developing and testing theories of what the problem is based on the information gathered in trouble shooting Introduction Diagnosing an engine is an art form that is built upon several factors First and most importantly is a good under standing of how the engine works The second is skills that have been honed by experience Finally the use of visual observations and a structured systematic approach to troubleshooting a problem The first part of this chapter will outline the steps of troubleshooting an engine so a technician can form a proper diagnosis The second half of this chapter will describe specific procedures and tests to perform while troubleshoot ing The first two rules in troubleshooting is to cause no further harm to the engine and prevent VAcaurion injuries Always make sure to check the oil for level and condition before starting an engine Also check attachments for damage and make sure they are firmly mounted Steps to troubleshooting NOTE The steps and the order of the steps that follow are a suggested approach to troubleshooting the MTD engine The technician does not necessarily have to follow them as described in this chapter Define the problem The first step in troubleshooting is to define the problem e Crankshaft will not turn A Hard to pull rope steady pressure
35. D Cylinder head removal Hemove these screws Sf 10 mm i wrench size u p Heat baffle mu ai j z H Figure 9 2 The Cylinder head of the MTD engine can be removed without removing the engine from the piece of equipment To remove the cylinder head 1 Disconnect and ground the spark plug high tension lead 2 Remove the spark plug using a 13 16 or 21mm wrench 3 Rotate the crankshaft until it is at TDC of the com pression stroke by following the steps described in the valve lash section of Chapter 1 Introduction 4 Remove the muffler and heat shield by following the steps described in Chapter 8 Exhaust 5 Remove the control panel carburetor and insulator plate by following the steps described in Chapter 3 Air Intake Systems 6 Remove the two screws that secure the upper left side of the blower housing See Figure 9 1 7 Remove the heat baffle See Figure 9 2 97 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines 8 Remove the screw that fastens the throttle lever to the rear of the cylinder head using a 10 mm wrench See Figure 9 3 NOTE The throttle lever can be disconnected and removed from the engine or moved to the side 9 Remove the five screws securing the valve cover using a 10mm wrench See Figure 9 4 10 Loosen the jam nuts and fulcrum nuts that secure the rocker arms using a 10mm wrench a
36. Engines Cylinder head installation 1 Place a new head gasket on the cylinder allowing mmm pe Graphite head the alignment dowels to hold it in place RS eU See Figure 9 8 NOTE MTD uses graphite head gaskets that have a bead of silicon on them They are not reus able 2 Position the cylinder head on the engine block 3 Install the 4 head bolts and tighten them to a step torque of 38 41 ft lb 52 55 Nm in an alternating diagonal pattern See Figure 9 9 NOTE The bolt closest to the exhaust valve must be the last bolt tightened Failure to do so will result in the head bolt loosening up NOTE The 490 engine has an over sized bolt with a Belleville washer in the number 4 position Insert the push rods Install the rocker arms x Adjust the valve lash by following the steps Figure 9 9 described in Chapter 1 Introduction Install the throttle lever and the heat baffle Install the muffler by following the steps described in Chapter 8 Exhaust Install the carburetor and engine shroud using new gaskets by following the steps described in Chapter 3 Air Intake 10 Testrun the equipment in a safe area before returning it to service Check all safety features 100 WWwW mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 Valves Cylinder head The valves and valve seats can be serviced by grinding and lapping or the head can be replaced Depending on local machine and labor cos
37. Excessive alcohol in fuel creates a lot of problems for gasoline engines One of the biggest problems is that alco hol attracts and holds water This corrodes the metal components of the fuel system especially the carburetor Alco hol also does not produce as much heat as gasoline when burnt This results in less power for the engine A 10 alcohol mix E10 is acceptable for MTD engines Anything higher than that will result in performance issues NOTE E85 and E20 fuels are not to be used in any MTD engines NOTE Use clean fresh fuel with a pump octane rating of 87 or greater e Stale or out of date fuel is the leading cause of hard starting issues nareas that have high amounts of alcohol in their fuel high octane fuel may improve engine performance and startability Fuel filters Dirty fuel can clog the carburetor and introduce abra sive materials into the engine To help prevent that MTD Nipple engines are equipped with a fuel filter The fuel filter is part of the fuel tank nipple See Figure 1 8 fuel filter Figure 1 8 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines To replace the fuel filter To avoid personal injury or property Awarnine damage use extreme care in han dling gasoline Gasoline is extremely flammable and the vapors are explosive Serious personal injury can occur when gasoline is spilled on yourself and or your clothes which c
38. Figure 8 4 NOTE The MTD engine uses a graphite exhaust gasket It is not reusable and must be replaced every time the muffler nuts are loosened NOTE The graphite exhaust gasket transfers heat from the cylinder head to the muffler The heat transfer helps to keep the engine oper ating temperature under control Do not sub stitute an exhaust gasket made from another material NOTE If reusing the muffler skip to step 8 4 Disconnect the manifold pipe from the muffler using a 13mm wrench 5 Clean all of the gasket material off of the manifold pipe and the muffler Figure 8 5 92 WWwW mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 Exhaust 6 Remove the four screws that secure the outer heat shield to the muffler See Figure 8 6 7 Slide the outer heat shield off of the muffler NOTE The inner heat shield is serviced with the muffler 8 Install the muffler by following the previous steps in reverse order NOTE Install a new gaskets between the muffler and the manifold pipe also between the manifold pipe and the cylinder head uw Ww m m m m NW NOTE Tighten the muffler and the manifold nuts to a Outer heat shield torque of 13 16 ft Ibs 18 22 Nm i Test run the engine before returning to service Figure 8 6 d Elie g 93 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines Muffler removal
39. For Parts Call 606 678 9623 or 606 561 4983 For A Gro For A Growing World MTD Professional Shop Manual 78 83 90 Series Horizontal Shaft Engines 277 357 420 cc Engines NOTE These materials are for use by trained technicians who are experienced in the service and repair of outdoor power equipment of the kind described in this publication and are not intended for use by untrained or inexperienced individuals These materials are intended to provide supplemental information to assist the trained technician Untrained or inexperi enced individuals should seek the assistance of an experienced and trained professional Read understand and follow all instructions and use common sense when working on power equipment This includes the contents of the product s Oper ators Manual supplied with the equipment No liability can be accepted for any inaccuracies or omission in this publication although care has been taken to make it as complete and accurate as possible at the time of publication However due to the variety of outdoor power equipment and continuing product changes that occur over time updates will be made to these instructions from time to time Therefore it may be necessary to obtain the latest materials before servicing or repairing a product The company reserves the right to make changes at any time to this publication without prior notice and without incurring an obligation to make such changes to previously publi
40. ORTC gapped to 0 026 0 030 0 65 0 75 mm See Figure 1 2 NOTE The F6RTC plug is the only plug that is EPA certi Figure 1 2 fied for the MTD engine 2 Wear rate will vary somewhat with severity of use If the edges of the center electrode are rounded off or any other apparent wear damage occurs replace the spark plug before operating failure no start occurs 3 Cleaning the spark plug NOTE MTD does not recommend cleaning spark plugs Use of a wire brush may leave metal deposits on the insulator that causes the spark plug to short out and fail to spark Use of abrasive blast for cleaning may cause damage to ceramic insulator or leave blast media in the recesses of the spark plug When the media comes loose during engine operation severe and non warrantable engine damage may result 4 Inspection of the spark plug can provide indications of the operating condition of the engine e Light tan colored deposits on insulator and electrodes is normal e Dry black deposits on the insulator and electrodes indicate an over rich fuel air mixture too much fuel or not enough air e Wet black deposits on the insulator and electrodes indicate the presence of oil in the combustion cham ber e Heat damaged melted electrodes cracked insulator metal transfer deposits may indicate detonation e A spark plug that is wet with fuel indicates that fuel is present in the combustion chamber but it is not being ignited www
41. a X e t ri Figure 4 12 3 Attach a vacuum pump to the vent port of the char coal canister See Figure 4 12 1 pm i ac i f E d E b 4 Apply a vacuum to the canister i Charc al canister NOTE When applying the vacuum squeeze the pump slowly Too much vacuum can close the roll over valve giving a false reading 5 If the canister does not hold a vacuum the canister and the roll over valve are working properly NOTE If the canister does hold a vacuum test the roll over valve to determine if the roll over valve or the canister is at fault Figure 4 13 44 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 FUEL SYSTEM AND GOVERNOR Testing the roll over valve The roll over valve vent has two functions The first function is to vent the tank and the second function is to close off the vent if the tank is inverted Hose to roll over valve T Test the roll over valve by OU ae i Disconnect the hose that runs from the charcoal de i canister to the roll over valve See Figure 4 14 2 Connect a vacuum pump to the hose 3 Slowly apply a vacuum to the roll over valve NOTE If the roll over valve does not hold a vacuum replace the canister 4 If the roll over valve held a vacuum disconnect the hose from the roll over valve 5 Attach the vacuum pump directly to the roll over valve 6 Slowly apply a vacuum to the roll over valve Figure
42. ailure of the lubrication system is probably not the cause As an example a piston skirt shows metal transfer to the cylinder wall The connecting rod and wristpin show some signs of excessive heat The main bear ings and camshaft are not damaged This would AS indicate that the problem was probably related to Metal to metal cylinder temperature transfer SUE ee ctum The hall mark of a lubrication failure is the presence of discoloration and or metal transfer on all friction ao surfaces within the engine See Figure 11 7 Figure 11 7 An important thing to note is that just because there are signs of insufficient lubrication that does not mean that was the cause of the failure It may only be a symptom of the real cause of the failure Larger size abrasive particles can render the lubri cants ineffective leading to an engine failure An over heated engine can cause the oil to break down leading to a failure In an engine overspeed the oil is pushed away from the bearing surface leading to a failure In all three of the above cases the signs of insufficient lubrication are symptoms not the cause There will also be signs of heat or discoloration around the parts affected by the lack of lubrication See Figure 11 8 Figure 11 8 124 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 Failure Analysis Engine Overspeed The MTD engine is designed for a maximum speed of 3600 rom When the g
43. all 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines 5 Carefully lift the spring and pulley out of the recoil housing See Figure 6 9 The recoil spring is under tension YAcaution and can release as the pulley is removed Eye protection should be worn while removing the starter pulley NOTE If the spring is undamaged but has been removed from the pulley the spring may be re wound Hook the end of the spring into the slot in the outer lip of the recess of the er pulley and wind the spring into therecessin o 3 Poe a counter clockwise direction E s E Jua uw cid r ur rs NOTE Evaluate the damage including parts prices Figure 6 9 and local labor rates In some parts of the country it makes economic sense to replace the complete assembly in other areas labor rates favor repair 6 To re assemble apply a small amount of lithium based chassis grease to the surface of the recoil housing that contacts the spring NOTE Use low temperature grease on the snow engines re Carefully position the pulley and spring in the recoil housing Rotate the pulley gently counter clockwise until the spring seats allowing the pulley to fall into position 8 Install the torsion springs and pawls so that the long E arm of the spring reaches outside of the pawl and draws it toward the center of the assembly See Figure 6 10 NOTE The rolled end of the pawl fits in the recess in th
44. an ignite Wash your skin and change clothes immediately 1 Siphon the fuel out of the fuel tank 2 Remove the front fuel tank shroud using a 10 mm wrench See Figure 1 9 3 Remove the fuel line from the fuel tank nipple 3a Squeeze the tabs on the fuel line clamp with a pair of pliers while sliding the clamp down the fuel line away from the nipple See Figure 1 10 3b Gently work the fuel line off of the nipple Hesidual fuel in the fuel tank will Awarnine come out when the fuel line is removed Safety goggles are recom mended to help prevent gasoline from splashing into your eyes Remove the fuel tank nipple using a 17 mm wrench Figure 1 10 Install a new filter by following the above steps in reverse order NOTE Apply a small amount of releasable thread locking compound such as Loctite amp 242 blue and tighten the filter by hand and then an additional 3 4 to 1 full turn to compress the gasket 10 WWwW mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 Introduction Valve lash Valve lash is the clearance between the top of the valve stem and the rocker arm The valve lash should be checked after the first 25 hours of use and every 100 hours after that Valve lash can be checked and adjusted using the following steps Spark plug socket A 1 Ifthe engine has been run allow it to cool thoroughly Position the equipment for easy access to the cylin M Y Ls m der head Ga 2 D
45. arnine Gasoline is extremely flammable and the vapors are explosive Avoid all sources of heat when working on the fuel system e Drain the fuel tank before starting work to prevent spillage e Dispose of drained fuel in a safe and responsible manner 40 WWwW mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 FUEL SYSTEM AND GOVERNOR The fuel tank To remove the fuel tank 1 Drain the tank 2 Remove the four screws that secure the fuel tank using a 12 mm wrench See Figure 4 5 Remove these screws xd 3 Figure 4 5 3 Liftup on the fuel tank and disconnect the fuel line See Figure 4 6 P Disconnect the fuel line ae 1 w i 1 P a d Fi rd r x E s E E o OE Figure 4 6 NOTE On engines equipped with an EVAP system dis connect the hose from the roll over valve See Figure 4 7 Roll over valve 4 Install the fuel tank by following the above steps in reverse order away 220 um Suep Jmajous gj Jauugi 3uo ce U aL ap apo np juasinpold sinau S814 4 i wad aj aie ap UBA Sani 8jDUJ 8j Z95SIE a TEtULUPjUI Sa aaua Buijanjea arr o ws wy ort o aj rouiPunuap adig ap jug i12 ISU 5g IU eiligdi d Figure 4 7 41 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines Evaporative EVAP emissions system Gasoline is made from the graduated distillation of crude oil It consi
46. arter rope and check the action of the pawls NOTE If starter rope tension needs to be adjusted hook the rope into the notch in the pulley and wind the pulley a couple of turns to add tension See Figure 6 6 10 Install the starter and tighten the starter nuts to a torque of 53 71 in Ibs 6 8 Nm a Figure 6 6 72 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 Starter and Charging System Starter pulley and recoil spring If damage is suspected the recoil may be disassembled by NOTE The recoil spring is nested within the starter pulley and both parts are sold as a single part number Eye protection should be worn if the starter pulley is to be removed 1 Remove the starter by following the steps described earlier in this chapter 2 Relieve the spring tension by 2a Pull some slack in the rope inside of the starter 2b Hookthe rope into the notch in the starter pul ley 2c Wind the pulley clockwise until all tension is removed 3 Remove the shoulder screw and pressure plate using a 10 mm wrench See Figure 6 7 eres m orsion springs p aN S Na ite jt ia NOTE Beneath the pressure plate is a compression spring and two starter pawls that are held in the disengaged position by two torsion springs 4 Inspect the pawls and torsion springs for wear and damage See Figure 6 8 Figure 6 8 73 www mymowerparts com For Parts C
47. atch is polished off that is a sign of dirt ingestion The cylinder can not be re honed because replacement piston rings are not available The engine must be short blocked 111 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines Balance Shaft 483 amp 490 There are two primary motions that generate most of the vibrations in single cylinder engines the rotation of the crankshaft and the reciprocating motion of the piston See Figure 10 16 pe Connecting r J 3278 y 7 Piston travels V 9p fi 4 A f vi M 1 U B e A X N E 3 I ZZ Co d T aw i The connecting rod translates the linear motion of the piston to the rotating motion of the crankshaft Two thirds of its mass can be attributed to rotating motion and one third of its mass can be attributed to reciprocating motion See Figure 10 17 If you balance the rotational mass perfectly by adding weight to the crankshaft counter weights there will still be a large force generated by the reciprocating masses the piston piston pin and one third of the connecting rod The crankshafts on MTD engines are not balanced Extra weight is added to the crankshaft counter weight to reduce the total reciprocating and rotational forces This causes the engine to shake side to side perpendicular to the crankshaft but reduces overall vibrations Reciprocating mass Piston s
48. chart Leak down Testing Results Symptom Possible cause Air escaping from Worn cylinder or piston rings the breather Possible blown head gasket Air escaping from Leaking exhaust valve the exhaust Air escaping from Leaking intake valve the carburetor Gauge reading Cylinder and piston rings are in low good condition Gauge reading There is some wear in the moderate engine but it is still usable Gauge reading excessive wear of cylinder and high or piston rings Engine should be short blocked or it could be a blown head gasket 25 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines Compression test To perform a compression test NOTE Compression should be in the range of 40 75 PSI 2 8 5 2 Bar e Disconnect the high tension lead from the spark plug and ground it well away from the spark plug hole e Remove the spark plug using a 13 16 or 21mm wrench A flexible coupling or wobbly extension may help e Pull the starter rope several times to purge any fuel or oil from the combustion chamber NOTE Air compresses readily liquid does not Liquid in the combustion chamber will result in an artificially high compression reading l l Compression gauge 1 fos a compression idi in the spark plug hole T vim UN Reading 40 PSI 2 Confirm that the gauge is zeroed then pull the TN starter rope repeatedly until the needle on the gauge stop
49. cup assembly by plac ing the washer on the inside of the crank case cover See Figure 4 45 6 Apply a small amount of releasable thread locking compound such as Loctite 242 blue to the gover nor pin T Position the governor gear and cup assembly with the pin in the hole in the crank case cover 8 By gently striking the governor cup drive the gover nor pin into the crank case cover until it is flush with the out side of the cover 9 Install the crank case cover by following the proce dures described in Chapter 10 Cam Crankshaft and Piston 10 Install the engine onto the equipment it came off of 11 Testrun the engine in a safe area before returning it to service Figure 4 46 60 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 Governor adjustment FUEL SYSTEM AND GOVERNOR To adjust the governor bi on arm Figure 4 47 1 Remove the fuel tank by following the procedures described in the fuel tank section of this chapter Loosen the governor arm nut but do not remove the nut completely Pry open the governor arm crimp with a flat head screwdriver See Figure 4 47 Using pliers grab the flat section at the top of the governor shaft and rotate it in a counter clockwise direction as far as it can go Push the governor arm to the right the spring should pull it in this direction NOTE Rotating the shaft counter clockwise will ensure the governor cup is
50. de 78 0 633 83 0 633 90 0 636 16 17 0 637 16 18 0 633 Cam shaft bearing max ID cylinder block 78 0 639 83 0 639 90 0 638 16 20 0 639 16 22 0 639 Cam shaft bearing max ID Sump 78 0 639 83 0 639 90 Balance shaft min OD cylinder block side 78 83 90 Balance shaft min OD sump side 78 83 90 78 83 90 Balance shaft bearing max ID sump N A 0 587 N A N A 0 592 0 592 0 591 15 00 0 591 15 00 www mymowerparts com Service Limit mm 31 42 32 24 32 24 31 52 31 73 31 73 16 09 16 09 16 09 16 09 16 09 16 09 16 22 16 22 16 22 16 22 16 22 16 22 N A 14 90 14 90 N A N A 15 03 15 03 For Parts Call 606 678 9623 or 606 561 4983 Crankshaft piston and connecting rod Specification New Min New Max Service Limit in mm in mm in mm Balance shaft bearing max ID cylinder block 78 83 90 Compression ring to land max clearance N A N A 78 83 S e Scrapper ring to land max clearance 0 008 0 20 78 0 20 83 0 20 90 0 20 Compression ring end gap 78 0 20 83 0 20 90 0 008 0 20 0 016 0 40 0 039 0 20 Scraper ring end gap 78 0 039 0 20 83 0 039 0 20 90 0 008 0 20 0 016 0 40 0 039 0 20 117 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines Minimum Maximum In mm Intake valve lash 78 0 006 0 15 83 0 006 0 15 90 0 004 0 10 0
51. does not start check the fly wheel key If the fly wheel key is intact the problem is not in the ignition system Check the engine s compression 5 If no sparks or weak sparks are seen in the spark tester use the electric starter to spin the engine NOTE If sparks are now seen in the spark tester check the module air gap If no sparks are seen further test ing is required Test the stop switch by following the steps described in the stop switch section of this chapter If the stop switch is working properly inspect the flywheel and flywheel key If the flywheel and key are OK replace the module 81 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines Stop switch All MTD horizontal engines that are in use in North America have a stop switch built into the throttle lever UEM DL assembly MTD engines used on snow blowers have an Disconnect swiic y eo additional stop ignition switch in the engine shroud D t To test the stop switch throttle 1 Remove the control panel by following the steps described in Chapter 3 Air Intake Systems 2 Test the remote ignition stop switch first by follow ing the procedures described in the next section of this chapter 3 Disconnect the lead that runs from the module to the stop switch See Figure 7 2 NOTE The blower housing was removed for picture clarity 4 Connect one lead of a digital multimeter to the
52. e area before returning it to service Check all safety features 103 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines 104 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 Crankshaft piston and connecting rod CHAPTER 10 CRANKSHAFT PISTON AND CONNECTING ROD The exact procedure a technician uses to disassemble an engine depends on the type of repairs needed This chapter is written as a set of procedures that should provide the user with sufficient information to complete any fea sible repair to the engine short block assembly The instructions are written with the assumption that the engine has been removed from the equipment These are bench work instructions 1 Drain and save the oil from the engine by following the steps described in Chapter 1 Introduction Hemove the fuel tank by following the steps described in Chapter 4 Fuel system and Governor Remove the air intake and carburetor by following the steps described in Chapter 3 Air Intake Systems Remove the starter by following the steps described in Chapter 6 Starter and Charging Systems Remove the flywheel and ignition module by following the steps described in Chapter 7 Ignition system Hemove the muffler by following the steps described in Chapter 8 Exhaust Remove the cylinder head by following the steps described in Chapter 9 Cylinder Head Remove the dipstick tube 9 o D Soe Se
53. e engine The vibration can also lead to fasteners loosening up Evidence of this could be elongated mounting holes The area around the mounting holes may be polished due to the two surfaces rubbing against each other 3 When an engine overspeeds the moving parts can not pull the oil in between them This allows metal to metal contact Because of this signs of inadequate lubrication will show 4 When trying to diagnose an overspeed failure look at all the pieces Individually the lack of lubrication piston position and condition of the connection rod will usually indicate separate failures Collectively they would indi cate an overspeed failure 125 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines Overheated The MTD engines are air cooled engines Because of this cleanliness of the engine is very important to the life of the engine Dirt grass and sludge all form an insulating layer on the engine This will trap the heat in the engine and cause it to over heat As metal parts heat up enough to change their proper ties they will take on a yellowish or blue cast As oil is heated to the point that it evaporates black deposits are left behind This is called coking An engine with lots of coked oil deposits inside the crankcase or cyl inder head indicates that it has been over heated See Figure 11 9 Another sign of an overheat failure is warped parts As
54. e starter pulley The bent end engages the starter cup The roll faces inward and the hook faces outward Figure 6 10 NOTE The extrusions on the pressure plate should fall inside of the pawls as the starter is assembled NOTE Drag on the pressure plate from the friction between the compression spring and the head of the shoulder screw causes these extrusions to force the pawls outward engaging the starter cup 9 Apply a small amount of thread locking compound such as Loctite 242 blue to the threads of the shoulder screw and install the screw Tighten it to a torque of 71 89 in Ib 8 10 Nm 10 Install the starter rope by following the steps described in the previous section of this chapter 11 Install the starter and tighten the starter nuts to a torque of 53 71 in Ibs 6 8 Nm 14 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 Starter and Charging System Electric starter The electric starter is only available on the snow engine It is powered by an extension cord that is plugged into household 120 volt AC current The starter and switch assembly are one piece and are not serviceable To replace the starter assembly Remove these screws 1 Disconnect the extension cord 2 Remove the two screws that secures the switch box to the engine See Figure 6 11 3 Remove the starter by removing the two screws that hold it to the engine block using a 10mm socket and Bi a long extension S
55. ead DC voltage 8 Back probe the red wire of the charger harness See Figure 6 18 9 The multimeter should read 17 26Vdc 10 Ifthe results do not match what is listed above check the magnets on the rotor NOTE If the magnet are still magnetic replace the stator Figure 6 18 78 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 Starter and Charging System To remove replace the stator 1 Remove and ground the spark plug wire 2 Remove the flywheel by following the steps described in Chapter 7 Ignition System 3 Remove the baffle that covers the charger harness using a 10mm wrench See Figure 6 19 4 Slide the grommet out of the engine block See Figure 6 19 Grommet me d Figure 6 19 5 Remove the two screws that secure the stator with a 10mm wrench and lift the stator off of the engine See Figure 6 20 6 Install the stator by following the above steps in reverse order 7 Test run the engine in a safe area and retest the volt age output before returning to service Hemove these screws Figure 6 20 Rotor Rotor failures are extremely rare To check the rotor e Confirm that the magnets are firmly attached to the flywheel e Hold a screwdriver or a similar tool made of ferrous metal within a 1 4 of each magnet e Ifthe tool is drawn to the magnet the rotor is good 79 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Hori
56. econ s a sa x atta e cau E E Eu d Eee Be Bess 108 PISIOMINSDOCCION 443 poder ei dic e o a oo E qo eee c OP e c pod 109 Connecting rod inspection llle 111 Gylinder Inspecllol xs oes e PRESE XEESEXue bore eee oesaewes d beans 111 Balance Shaft 483 amp 490 0 ee eee 112 HOSgSSOIbly naruto dio ede Drm d ying GH ae qu hae eh ee eave aru s ede 113 Engine specifications chart llle 115 Engine torque values chart llle 119 Chapter 11 Failure Analysis Abrasive Ingestion 39 99 9 59 xb or Ee bare doe spa Pod oy okie sw doe errata 121 INSUTHICICNE IUDNCANON senssa ex te tos euh DEW UE REEARRERR eee twee 124 ENONCE OVerspegtl 2320 0 io EA EUER SUAE RR ed 125 Sacco REERTES TET TTC CL TEILT SIT S E 126 Mechanical Breakage Wear cee ee eee ees 127 Detonation preignition llle RII 127 www mymowerparts com M For Parts Call 606 678 9623 or 606 561 4983 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 Introduction CHAPTER 1 INTRODUCTION Professional Service Manual Intent This manual is intended to provide service dealers with an introduction to proven diagnostic and repair proce dures for 78 83 90 series MTD horizontal shaft engines Disclaimer The information contained in this manual is correct at the time of writing Both the product and the infor mation about the product are subject to change without notice About the text format
57. ed or missing flywheel key c The wrong flywheel or module is installed on the engine IV Insufficient inertia to over come normal compression a Loose implement b Alight flywheel used on a heavy flywheel application C Rope will not pull at all This is usually either a quick fix or a catastrophic failure The likely suspects are A broken starter recoil easy fix Il Complete hydraulic lock easy fix Ill External binding jammed implement easy fix IV Bent crankshaft unrepairable V Internal binding crankshaft connecting rod or piston unrepairable Crankshaft turns no start 2a Most gasoline engine diagnosis involves isolating problems in the four critical factors an engine needs to run properly l Ignition sufficient spark to start combustion in the cylinder occurring at the right time ll Compression enough pressure in the cylinder to convert combustion into kinetic motion It also needs sufficient sealing to generate the vacuum needed to draw in and atomize the next intake charge Ill Fuel correct type and grade of fresh gasoline in sufficient quantity atomized tiny droplets and in correct fuel air proportions IV Flow if all of the above conditions are met but the flow of air is constricted on the inlet or exhaust side it will cause the engine to run poorly or not at all This also includes ensuring the valves are timed to open at the proper time 2a Isolate the ignition system and comp
58. ee Figure 3 12 Residual fuel in the fuel tank will Awarnina come out when the fuel line is removed Wear safety goggles to help prevent gasoline from splashing into your eyes Remove the fuel line from the fuel tank Figure 3 12 34 WWwW mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 AIR INTAKE SYSTEMS 4 Remove the Heat box snow engines or the control panel summer engines by following the steps described in appropriate section of this chapter 5 Disconnect the throttle linkage and spring See Figure 3 13 6 Slide the carburetor off of the mounting studs 7 Remove the carburetor NOTE The barb on the carburetor inlet is very sharp If The fuel line is pulled off of it the line will be dam aged and must be replaced Throttle linkage Throttle spring NOTE The carburetors are not inter changeable from one engine model to another To help prevent carbure tor mix ups the engine model number is stamped on the carburetor by the fuel nipple See Figure 3 14 Figure 3 14 m 8 Unhookthe ignition wires from the clip molded into TE the insulator plate See Figure 3 15 E H Figure 3 15 35 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines NOTE An insulator block separates the carburetor from the cylinder head There is a gasket on each side of the insulator See Figure 3 16 NOTE The gaskets are
59. ee Figure 6 12 Remove these j screws Figure 6 12 75 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines Pull back and angle the 4 Pull back on the starter approximately 1 2 Then starter away while angle it away from the engine while sliding it out of sliding it out the engine See Figure 6 13 i NOTE Before condemning a starter make sure to bench test it To bench test a starter A Remove the starter from the engine B Plug the extension cord into the switch housing C Hold the starter down and press the starter but ton e Ifthe starter works on the bench confirm that the engine crankshaft rotates with normal force e Ifthe crankshaft does not rotate with normal Figure 6 13 force identify and repair the engine problem NOTE This includes adjusting the valve lash e fthe crankshaft rotates with normal force but the starter is unable to turn it replace the starter e Ifthe starter does not work replace the starter 4 Install the starter by following the above steps in reverse order NOTE Tighten the starter screws to a torque of 195 221 in lbs 22 25 Nm 76 WWwW mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 Starter and Charging System Charging system Some engines are equipped with a charging system The charging system used on MTD engines consists of three components the rotor stator and the rectif
60. er or an electronic version of the same tool Less than 3 to 4 7 6 10 2cm of water is a typical reading at idle Figure 2 3 3 An engine that fails to purge extra case pressure in a controlled manner will build case pressure The pres sure will find it s own way out of the engine in unde sirable ways e Oil will be forced by the rings and valve guides being burnt in the combustion chamber The cause of this oil burning can be mistaken for a worn out engine if proper diagnosis compression leak down and case pressure is not performed 4 Experimentation by MTD s Training and Education Department has revealed the following characteristics of MTD engines e A leaky PCV system will not build up substantial case pressure e A leaky PCV system will allow the engine to ingest contaminants through the system accelerating engine wear A blocked PCV system will allow crankcase pressure to build very rapidly Noticeable oil fumes will be evident in the exhaust within several minutes of normal operation 27 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 AIR INTAKE SYSTEMS CHAPTER 3 AIR INTAKE SYSTEMS MTD builds horizontal crank engines for snow blowers and chore performers The differences between snow engines and chore engines are the muffler and the air intake system Therefore the ai
61. ers Show englh6S 2 acer edo pex a dba n e t 50 arb elo Se s 2dcee qr ot dein o eo qe ROG nio Jo ac Re cd De SR dd escis 51 Inspecting the carburetor llle 51 Disassembly and rebuilding of the carburetor Lss 52 FUCK SNULOIM VaIVe 43 55 mper Ex RE bur puedes ee bere ma d basics cg 56 GOVE MO ue acia ante dox d b eddie e ee he ated Se ie 58 GOVEIMNOF AN terser ret Ec DC rac b Tracy Sce od d aba CR id a D o P 58 over Do Shall usted od ema Dic oe rode Me Spes qd Geode rd fo Ses 59 Governor cup and the governor gear 0 ce eee ee 60 Governor adjustment 0 eee eens 61 Chapter 5 Lubrication Oll type and guany uen eee hee E re e pees d dd RE rs 63 OMG SUCK suuin doit VOL ur dela duo Sub Sod dedu dos Mesue oe da fo ie 64 Dip SICK tube removal 2cer ccceteeSen og boat he beneeded see ae dae es 65 LUDICAION SVSICMN s ua dc xe earners byt eeu Ss eee video 66 Positive crankcase ventilation valve 2 0 0 ees 67 Chapter 6 Starter and Charging Systems Recoil Starter Removal 2 2 2 rodan a aea lll llic 69 olane HD 222 4 ado SC PvE Ee dun ae OR ORAE EC Xd EP 70 Sele Mn e ui eu EE ERE ee a pae ee ee ee EI E E 71 Starter pulley and recoil spring llle 73 EIEC Sla NE RR e T TU TT TT T TT 19 Charging Sy SEIT s e curus scar neve aa DE RH ee eee eee Bee A 77 Gharging Systemi testing x i Ed ERU EX E ebawawes d beads 78 vitziro P EEE inure don ENE ee ee See Paes Meee aaa eee 79
62. filter either squeeze it in side of a paper towel or let it air dry DO NOT wring it because the filter will tear Before installing any foam filter after it has been washed it needs to be free of moisture NOTE Always check with factory specification prior to servicing replacing any engine components NOTE Do not oil the foam pre filter The paper filer will absorb the oil and it will become plugged WWwW mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 Introduction Oil type and capacity MTD engines use oil with a SF SG API rating or better is the recommended oil for this engine The winter engines use SAE 5W 30 oil and the summer engines use SAE 10W 30 oil The oil capacity for all of the 78 83 90 series engines is 37 fl oz 1 1 liters e Check the oil level frequently and change the oil more frequently in severe operating conditions such as exceptionally deep snow falls e Synthetic oil is a suitable alternative but it does not extend service intervals NOTE MTD recommends the use of petroleum oil during the break in period to ensure the piston rings cor rectly break in e Synthetic vs Petroleum based oil To simply look at synthetic oil and to compare it with Petroleum based oil there is very little difference However when you look at the two through a microscope it is easy to see the difference Synthetic is made up of smaller molecules This allows the oil to get into areas that petro leum based oil cannot
63. fuel tank Tethered Figure 4 9 3 The vapors are routed through the charcoal canister See Figure 4 10 4 The activated charcoal inside the canister absorbs the hydrocarbons allowing the air to pass through and out to the atmosphere AIR Charcoal canister Figure 4 10 5 The second line on the charcoal canister goes to the control panel When the engine is running vapors LM N are drawn out of the charcoal canister by the air being drawn into the carburetor This re charges the canister of the next down period See Figure 4 11 A IR Charcoal canister Figure 4 11 43 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines Troubleshooting the EVAP System There are four failure modes for the EVAP system e A leak in the system will allow dirt ingestion e A blockage in the system between the canister and the fuel tank acts a plugged vent e A blockage in the system between the canister and the control panel The canister can not purge its vapors e Charcoal canister poisoned raw fuel in the canister prevents the canister from absorbing fuel vapors NOTE The only failure mode that will affect the operation of the engine in a way the operator will notice is a blockage in the system To test the system for a blockage 1 Remove the fuel cap 2 Clamp off the hose that runs from the canister to the control panel See Figure 4 12 v
64. g mark points to the tappets ae Timing marks E 8c Insert the cam shaft while aligning the timing E marks See Figure 10 22 Place a new gasket on the crankcase cover let the alignment dowels hold it in place Using a seal protector slide the crankcase cover on to the crank shaft d M w wl Gently rock the crank case cover while rotating the Figure 10 22 crankshaft until it seats fully against the cylinder block Install the crank case cover bolts and tighten to a torque of 80 106 in lbs 9 12 Nm NOTE Use a star torque pattern to tighten the cover bolts Install the cylinder head by following the steps described in Chapter 9 Cylinder head Install the muffler by following the steps described in Chapter 8 Exhaust Install the fuel tank by following the steps described in Chapter 4 Fuel systems and Governor Install the carburetor by following the steps described in Chapter 3 Air Intake and Filters Install the flywheel and module by following the steps described in Chapter 7 Ignition system Install the blower housing and starter by following the steps described in Chapter 6 Starter and Charging Sys tems Install the engine on the application by following the steps described in the application s service manual Install the spark plug by following the steps described in Chapter 7 Ignition system Fill the engine with oil and fuel by following the steps described in Chapter 1 Introduction Test run the engine i
65. g rod bearing surfaces NOTE Connecting rods are not available as service parts Figure 10 14 If the connecting rod is bad the engine must be short blocked 4 Take the crank pin and piston pin measurements and subtract them from the connecting rod measurements to get the connecting rod to journal running clearance and the piston pin to connecting rod running clearance Compare that number to the one listed in the chart at the end of this chapter NOTE Plasti gauge can be used to measure the connecting rod to journal running clearance but it is very technique sensitive and it is not as reliable as the method described above Cylinder inspection 1 Clean and inspect the cylinder inside and out Measure the cylinder bore op y NOTE If there is any sign of damage especially cracked cooling fins short block the engine wo NOTE Take two measurements of the cylinder bore 90 degrees apart at the top bottom and middle of the cylinder See Figure 10 15 NOTE The measurements can be made using telescop ing gauges inside micrometers or dial indicating bore gauge Hg 2 Compare the measurements to those that are listed in the chart at the end of the chapter The bore should not be worn too large piger e The bore should not be tapered The bore should be round not oval shaped 3 Inspect the cylinder cross hatch NOTE The cross hatch is important because it helps hold oil on the cylinder walls NOTE If the cross h
66. ght side of the engine at the bottom of the block See Figure 1 1 NOTE The serial number will always start with the model number Front of engine AN I VL 12042A0009 nu E m ats Model serial number Ss Figure 1 1 MTD Horizontal Engine Model Designators Starter Alternators 1 Recoil start 2 Electric start 3 E start alt 20N 20W 4 E start alt 3A DC 5A 161 SHA Major Revision Change Compliance United States 50 State Europe California 49 State U S 49 and Europe U S 50 and Europe Bore Dia mm End Product Chipper Shredder Snow No tank Logsplitter Tiller slow reverse Snow Tiller Verticutter MTD Engine Serial Numbers 1P65 _1P65FH 051027 1A0023 Producing Linet Line A 1 shift B 2 shift www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 Introduction Maintenance The information in this manual applies to the MTD engine Some basic principles may apply to engines pro duced by other manufacturers As the saying goes an ounce of prevention is worth a pound of cure The same can be said about preventive maintenance on outdoor power equipment By changing the spark plug and oil at recommended intervals many fail ures can be avoided NOTE Please refer to Chapter 7 Ignition for the complete service instructions on spark plugs 1 The spark plug used in the MTD engine is a F
67. hat could cause the problem 18 Repairing the problem lleeeel nh 23 PRIMO Sl x chase acest harder de Beal ar aac a alae ee os ee T noe aes 24 EGQaK dOWLD ICS cuiu coke S dk ahi ebd e LE Bead m oe eos 24 CCOmpressiol tesL 4 verdes SE ESEEIE ERA Wu ees push Sie exis 26 PCV eSNG S aso iere eh eee eee eee teh eee eee TERES EXE 27 Chapter 3 Air Intake systems Heat box snow engines 0 ee eee 29 Air filter summer engines 0 000 ees 30 Air filter base and control panel summer engines 32 Carburetor and Insulator l l 34 www mymowerparts com II For Parts Call 606 678 9623 or 606 561 4983 Chapter 4 The Fuel System and Governor Inspec ng the TUGl 3 mr rp E EXE eee Re eee dt Gu a 37 TeSL IDEO ale OO 8222s Gans ett atna petens duo P3 aes 38 Fueltank Vell sucus Era EE oe tate deh tee X auae es 39 Te TOC T OE 645 suntin dO ost et ER IER SCREEN DI UL ALES EE a 40 Inspect the fuel lines 6242626420 dedu dox oe bo do eodera dw Ae et 40 TACTUCITANK uu aat dard doded um ut GER he ee Eod E TR CH Dh t 29 dide iie edes 41 Evaporative EVAP emissions system llle 42 Troubleshooting the EVAP System llle en 44 Cna Oea EE 4 0 3 4 e rbpt a kp vea doter wb lo three yg Boats 46 HOILOVEF VAING duod cione Geo Mita oe bk oe ae dr abbat ai donet 47 OKC 3 acies tate Ronee Sa COR 9 aS DURO Roos EA he a a URS Dons aote 48 Prim
68. he activation threshold This will have no ill effects on engine performance Half engine speed clatter loose valve lash e Half engine speed clatter slightly heavier wrist pin e Rhythmic heavy light engine speed click piston slap C Spark knock Advanced ignition timing 21 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines Low octane fuel Over heating engine check for blocked cooling air flow Carbon build up in cylinder glowing carbon chunks pre igniting air fuel mix d Chirp e Compression blowing by the fire ring of a damaged head gasket will sometimes produce a chirping noise Confirm with a compression test and leak down test e Unusual exhaust tone oplashy or blatty e Splashy idle usually indicates a slight rich condition May indicate an exhaust blockage usually slightly muffled Backfire e On over run unburned fuel igniting past exhaust valve Mixture not burning completely in com bustion chamber It may be too rich or it may be spark plug or ignition problem Occasional under load engine momentarily runs lean usually will cycle with float bowl level or governor pull in sometimes sounds like a slight stumble Ethanol content exceeding 10 will make the engine run artificially lean Skip Usually ignition related e Run the engine with a spark tester in line between the spark plug wire and the spark plug or use an oscillosc
69. ier e Alternator rotor The rotor consists of five magnets on the inside of the flywheel that rotate around a stator that is mounted to the cylinder block As the crankshaft and flywheel rotate the moving mag nets induce a charge in the stator See Figure 6 14 e Alternator stator The stator consists of copper field windings around an iron core The stator is attached to the engine block beneath the flywheel See Figure 6 15 e Rectifier A set of four diodes that convert the AC current into DC current The rectifier is built into the stator and it is not serviceable e Stator e v ara Figure 6 15 TT www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines Charging system testing To test the charging system 1 Locate the charger harness It will be by the right NEM e m handle bar of the snow thrower when the engine is installed See Figure 6 16 2 Start the engine and run it at full throttle e Charger Saa n harness o Figure 6 16 3 Connect the black lead of a digital multimeter to a NN v good ground on the engine h be Charger harness 4 Set the multimeter to read AC voltage Aye 7 ee P of Back probe the yellow wire in the charger harness bU with the red lead of the multimeter SUN See Figure 6 17 6 The multimeter should read a voltage of 13 18Vac D E Yellow wire T Set the multimeter r
70. ing A possible cause of this is loose valve lash V Makes unusual smoke when running a Black smoke usually heavy usually indicates a rich air fuel mixture e Not enough air air flow blockage or a partially closed choke Too much fuel carburetor float or float valve stuck or metering emulsion issues with the car buretor b White smoke usually heavy Oil in muffler usually the result of improper tipping The engine will fog for a minute or so then clear up on its own Massive oil dilution with gasoline It may be caused by improper tipping It can also be caused by leaky carburetor float valve if there is a down hill path from the carburetor to the intake port Check oil for gasoline smell repair carburetor c Blue smoke usually light PCV system May be blocked or unplugged May be over come by massive over filling or oil dilution with gasoline Will cause oil to exit the engine via any low resistance paths Piston rings e Confirm with leak down test e Smoke will be more pronounced under load e Repair may not make economic sense Valve guides and intake valve stem seal e Smoke will be more pronounced on over run VI Makes unusual noise when running a Knock Check for loose mounting of engine or driven implement Rotate crankshaft back and forth to check for loose connecting rod b Click Clicks and pops on engine shut down Compression release coming into play as the engine RPMs cross t
71. irpin clip from the governor shaft See Figure 4 43 Remove pe 6 Slide the governor arm out of the engine block from hairpin clip E the inside of the engine 7 Check the movement of the fly weights and cap on the governor gear iM 8 Install the shaft by following the above steps in 3 reverse order Figure 4 4 9 Install the engine on the equipment it powers 10 Testrun the engine and agjust the top no load engine roms by following the steps described in the carbure tor section of this chapter 59 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines Governor cup and the governor gear The Governor gear and cup are located inside the crankcase cover The flyweights and the governor cup are inter locked on this family of engines The governor gear and cup are serviced as a complete assembly 1 Remove the engine from the equipment that it pow ers 2 Remove the crank case cover from the engine by y w of following the steps described in Chapter 10 Cam JA tye N Crankshaft and Piston 3overnor pin 3 Position the crank case cover over an open vise so that the governor gear can pass through its jaws 4 Drive out the governor pin using a pin punch See Figure 4 44 NOTE There is a washer between the governor cup and the crank case cover this washer will fall out when the governor comes out 5 Install the governor gear and
72. isconnect the high tension lead from the spark plug Muffler and ground it well away from the spark plug hole WS 3 Remove the spark plug using a 13 16 or 21mm wrench A flexible coupling or wobbly extension may help See Figure 1 11 L M D T 1 Valve cover j Figure 1 11 4 Disconnect the breather hose from the valve cover See Figure 1 12 5 Remove the five bolts that secure the valve cover using a 10mm wrench Remove the valve cover from the engine NOTE If care is taken not to damage the valve cover gas ket it can be re used Figure 1 12 11 www mymowerparts com 10 11 12 12 For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines Slowly pull the starter rope until air can be heard coming out of the spark plug hole Confirm that the piston is at Top Dead Center on the compression stroke See Figure 1 13 e The compression stroke can be distinguished from the overlap stroke by the presence of air pressure at the spark plug hole and the fact that neither of the valves should move significantly on the compression stroke e There is an automatic compression release mechanism that bumps the exhaust valve as the piston rises on the compression stroke At TDC the exhaust valve should be fully closed Check valve lash between each valve stem and rocker arm using a feeler gauge Intake valve lash carburetor
73. l c Checkthe ignition and read the spark plug d Look for obvious signs of physical damage exhaust system blockage or cooling system block age Broken starter rope 3a Usually means the engine was hard to start 3b Makes it impossible to confirm any running or hard starting symptoms by direct observation 3c Some inference can be made from checking other factors of the general condition of the equipment Identify factors that could cause the problem 1 18 This is the second step in the troubleshooting process Crankshaft will not turn A Hard to pull rope steady pressure This usually indicates a mechanical bind of some sort The likely suspects are l A slightly bent crankshaft In some cases the drag may increase and decrease as the crankshaft rotates This produces a pulsing feeling that is different than a jerk back ll A parasitic load from a drive belt that is not releasing or an implement that is jammed Ill An internal drag from a scored or seized piston www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 BASIC TROUBLESHOOTING D Rope jerks back This usually indicates that the piston is stopping before top dead center on the com pression stroke and is being driven back down by compression or combustion The likely suspects are l Compression that is unusually high a valve lash b a partial hydraulic lock Ill Ignition timing is advanced a Improper air gap b Shear
74. lines up with the two posis in the carburetor fuel will flow to the needle valve Figure 4 39 7 Remove the rubber gasket See Figure 4 40 8 HRe assemble the fuel shut off valve by following the previous steps in reverse order 9 Testrun the engine before returning it to service Figure 4 40 57 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines Governor The engine speed is controlled by a balance between the force applied by a spring pulling the throttle open and a flyweight mechanism within the engine applying force to the governor arm pushing the throttle closed See Figure 4 41 NOTE While the mechanism is simple and robust it is important to pay attention when working on parts near the governor Binding caused by interference with mis routed lines or cables may make the governor unrespon sive g 7 NOTE When a governed engine hunts it is gen he 2 NL Boana a rather than a problem with the governor erally an indication of a lean fuel air mixture E c 4 i E 2 Za EE Figure 4 41 Governor arm To remove the governor arm from the governor shaft 1 Remove the fuel tank by following the steps described in the Fuel Tank section of this chapter NOTE Mark or note which holes the spring and linkage was in to ensure they go back in the same Loosen nut holes Unhook the governor spring e i A i Sp
75. metal parts heat up they expand In an engine a certain amount of expansion is expected Engines are built so that when parts are at operating temperature the parts will expand to be within the tolerances needed for the engine to run A problem occurs when the parts are over heated They expand more than they were designed to Some parts are mounted firmly like cylinder heads the hottest part of the engine As they try to expand they fight Figure 11 9 against the head bolts The head bolts will not move to allow the expansion so the head warps to allow the expansion This warping of the head allows the head gasket to leak A leaking head gasket allows the compressed gases in the engine to escape lowering the compression in the engine and hurting engine performance As the cylinder head cools it shrinks back down to its normal size but there will still be some warpage of the head See Figure 11 10 Localized over heating will leave localized hot spot indications such as discoloration Rapid over heating of a cylinder like when there is a cooling air flow obstruction may cause hot spots and metal transfer between the piston skirt and the cylinder wall Over heating of the cylinder head may be caused by lack of air flow or exhaust system issues Typical damage from this kind of over heating is a dropped valve seat A dropped exhaust valve seat combined with coked oil in the cylinder head would be sure indicators of an o
76. mn through a port about 1 2 1cm from the bottom to help prevent the ingress of any residue in the bottom of the bowl NOTE The orifice in the main jet meters fuel into the cen tral column NOTE Air from the main jet emulsion port enters the cen tral column near the top then gets bubbled through the emulsion tube into the metered fuel flow to promote atomization Figure 4 29 53 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines NOTE The main jet secures the emulsion tube in the central column of the carburetor See Figure 4 30 Emulsion air port mainjet Figure 4 30 10 Thethrottle stop screw has a large pliable lip around the head of the screw That lip secures a metering Welch plug plug for the pilot and transition ports Remove the screw to reach the plug See Figure 4 31 shot plug in feed bore Fuel port to central column Fuel feed leg on central column for pilot and transition Figure 4 31 Throttle stop 11 Carefully pry out the metering plug and spacer a Le using a small screwdriver See Figure 4 32 g 9 Spacer i Q Metering Figure 4 32 54 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 FUEL SYSTEM AND GOVERNOR End view 12 Examine the metering plug See Figure 4 33 Fuel drawn from the central column via the long fuel feed leg is metered by the brass orifice in the tip
77. n a safe area and make any carburetor and governor adjustments needed WWwW mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 Crankshaft piston and connecting rod Engine specifications chart Specification New Min New Max Service Limit In mm In mm In mm Bore digit 2 amp 3 of the model number 78 3 080 78 23 83 3 277 83 24 90 3 544 90 02 3 544 90 03 3 553 90 26 Crank pin min diameter 78 1 296 32 92 83 1 414 35 91 90 35 91 Piston pin min diameter 78 18 07 83 90 Connecting rod max 78 83 90 ID crank side 1 302 33 08 Connecting rod max ID piston side 78 0 719 18 25 83 0 797 20 26 90 0 796 20 22 0 796 20 23 0 797 20 26 Connecting rod to crank pin max running clearance 78 0 07 83 0 07 10 0 07 Connecting rod to crank pin max side clearance 78 1 24 83 1 24 90 1 24 Crank shaft run out max 78 0 03 83 0 03 10 0 001 0 03 0 001 0 03 0 001 0 03 Crank shaft end play max 78 0 035 0 88 83 0 022 0 55 90 0 000 0 00 0 022 0 55 0 022 0 55 www mymowerparts com 115 For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines 116 Specification Intake lobe height New Min in mm in mm in New Max 78 83 90 Exhaust lobe height 78 83 90 1 261 32 02 1 264 32 12 1 249 Cam shaft min OD cylinder block side 78 0 633 83 0 633 90 0 636 16 17 0 637 16 18 0 633 Cam shaft min OD sump si
78. nd a 14mm wrench 11 Pivot the rocker arms aside or remove them com pletely and remove the push rods NOTE Once broken in the rocker arm should be kept with its corresponding valve NOTE The intake and exhaust push rods are iden tical and interchangeable It is preferable but not absolutely necessary to return the same push rods to their original locations on engine with substantial 2100 hours operat ing time li h 12 If replacing the head double nut and remove the ets e exhaust and carburetor studs 13 Remove the cylinder head bolts using a 12mm s NOE in wrench See Figure 9 5 R pc e Figure 9 5 98 WWwW mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 Cylinder head NOTE The 490 engine has an over sized bolt with a Belleville washer in the number 4 position The wrench size and torque is the same as the other three bolts See Figure 9 6 14 Lift the cylinder head off of the engine Clean gasket i sp espn 15 Carefully clean all sealing surfaces of all gasket resi surface E tius NO NS i due Do not scratch the sealing surfaces 5 mE E Alignment See Figure 9 7 3 Del Es e EN dowels SH N passage JE we ZZ NOTE Make a visual inspection of the valves and cylinder ON p I i bore to confirm the initial diagnosis WARE Push rod chamber and oil T TEC Figure 9 7 99 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft
79. nd wire LI J JU a q d j v7 L i l F pF 1 i i IJ i ie i f Figure 7 9 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 Ignition System The module The coil in this ignition system is an inductive discharge magneto contained in a single module e The inductive discharge magneto has a two leg design e The magneto is energized by the passing of a magnet mounted in the flywheel e Ignition timing is set by the location of the flywheel in relation to the crankshaft Proper timing is maintained by a steel key Normal performance of the coil is to produce at least 10 000 volts at starter rope pull through speed The presence or absence of strong spark with the stop switch known to be good is generally enough to identify the ignition coil as good or bad Resistance readings may help confirm the source of the failure but are generally meaningless because they only measure a small part of the module NOTE No spark or a weak spark may be the result of an improper air gap The air gap space should be 0 016 0 024 0 4 0 6mm Simple spark testers are readily available and inexpensive Thexton Part 404 is available from a variety of retail ers and similar tools are available from other manufacturers See Figure 7 10 iag ynna anm suggested minimum salle j for no stan d 3m r Application Adjust T molles gli SE Instructions on back of package TYPICAL SPARK TESTER CONNECTION
80. nipple and slide it back Then remove the breather hose from the valve cover nip ple See Figure 5 7 3 Remove the five screws that hold the valve cover to the cylinder head using a 10mm wrench See Figure 5 8 NOTE The PCV valve is not serviceable If it is faulty the valve cover must be replaced 4 Reassemble the PCV and valve cover by following the above steps in reverse order NOTE Tighten the cover bolts to a torque of 62 79 7 in Ibs 7 9 Nm 5 Inspect the PCV tubing for cracks brittleness or signs of leaking Replace the PCV tube if any are found 6 Test run the engine before returning to service 67 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 Starter and Charging System CHAPTER 6 STARTER AND CHARGING SYSTEMS There are two starter systems available for the MTD engine The first one is a recoil starter and the second Is a 110 volt electric starter All of the 78 83 90 series MTD engines equipped with an electric starter are also equipped with a recoil starter Recoil Starter Removal To remove recoil assembly from the engine 1 Remove the three nuts that secure the recoil assem bly to the engine using a 8mm wrench See Figure 6 1 2 nstall the starter by following the above step in reverse order Tighten the screws to a torque of 53 71 in lbs 6 8 Nm
81. nkshaft NOTE Never strike the crankshaft directly with a hammer To prevent damage to the crank shaft use a brass drift punch or a piece of wood between the hammer and the crank UN shaft See Figure 7 14 Figure 7 14 If the flywheel shows any signs of physical damage such as cracks broken vanes or damaged VAcaurion key way replace it A damaged flywheel poses a threat of burst failure Burst failures are extremely hazardous to surrounding people and property 5 Inspect the key keyway and tapered mating surfaces of the flywheel and crankshaft NOTE If the key is damaged it must be replaced If there is damage to the crankshaft the engine must be short blocked because the crankshaft is not available as a service part NOTE On installation confirm that the key is properly seated the flat of the key parallel with the threaded section of the crankshaft in the keyway and that the tapers are fully seated Key or keyway failure may result from improper seating IMPORTANT The tapers in flywheel and on the crankshaft must be clean and dry The flywheel is held in place by the friction between the flywheel and the crankshaft not the key The key is only to guide the flywheel to the proper position until it is torqued down 6 Install the flywheel nut to a torque of 66 81 ft Ibs 90 110Nm 7 Adjust the air gap by following the steps described in the previous section of this chapter 8 Reassemble the engine 9 Test r
82. ntal Shaft Engines Test for ignition that won t turn off MTD engines are turned off by removing the spark from the engine This is accomplished by shorting the primary windings of the coil to ground If the engine does not stop when the key is removed and or the throttle is moved to the stop position 1 Test the stop switch and the remote ignition switch by following the procedures described in the previ ous sections of this chapter NOTE If the switches are working properly leave the front engine shroud off Remove the blower housing Move the throttle to the wide open throttle rabbit position 4 Connect one lead of the multimeter to one of the wires that goes to the remote switch NOTE One wire will go to one of the module screws to provide a ground path The other wire goes to the primary winding of the coil Set the multimeter to the ohms Q scale Connect the other lead of the multimeter to a good ground See Figure 7 8 7 Repeat steps 6 8 on the other wire See Figure 7 9 e The ground wire should have a resistance read ing of 0 2 Q or less If the reading is gt 0 2 Q check the ground at the module and check the wire for a fault e The wire that goes to the primary windings of the coil should have a resistance reading of approximately 1 0 Q If the reading is gt 1 2 Q replace the coil 84 L One of the wires Figure 7 8 d j Ground reading JN Tw M Grou
83. oduces a pulsing feeling that is different than a jerk back b Parasitic external load A bind in the equipment the engine is powering c Internal drag from a scored piston or similar damage IV Low governor setting or stuck governor a Check RPMs using a tachometer b RPMs should not droop under moderate to heavy loads V Low compression a Check valve lash b Check compression c Checkleak down to identify the source of the compression loss VI Flow blockage a Exhaust blockage usually accompanied by an unusual exhaust sound Just as a throttle on the carburetor controls the engine RPMs by limiting the amount of air an engine can breathe in an exhaust blockage will limit engine performance by constricting the other end of the system e The muffler itself my be blocked he exhaust valve may not be opening fully possibly because of extremely loose valve lash settings e The exhaust valve seat may have come loose in the cylinder head This may cause a loss of compression a flow blockage or it may randomly alternate between the two NOTE The cause of an exhaust valve coming loose is usually over heating 20 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 BASIC TROUBLESHOOTING b Intake blockage e An intake blockage up stream of the carburetor will cause a rich fuel air mixture and constrict the amount of air that the engine can draw in limiting performance The intake valve not fully open
84. oil assemblies is a broken rope NOTE If the spring was not damaged when the recoil sprung back it is possible to simply remove the rem nants of the old rope and install a new rope ca m wm 1 Remove the starter by following the steps described earlier in this chapter 2 Remove the old starter rope by prying out the starter cord knot and pulling the rope out with it Cut a piece of 6 recoil rope 75 1 9 meters long 4 Heat fuse the ends of the starter rope and tie a dou ble half hitch in one end 5 The rope may be easily installed from the outside in Pull the rope tight to seat the knot firmly in the recess in the back of the pulley See Figure 6 4 NOTE It may be necessary to wind the pulley clockwise to line up the hole in the pulley to the hole in the starter housing If so use a punch or screwdriver to block the pulley preventing it from rewinding See Figure 6 4 6 Wind the spring 6 7 turns and block it with a punch or screwdriver to keep it from rewinding 7 Install the handle and handle insert on the loose end of the rope again using a double half hitch See Figure 6 5 8 Remove the blocking tool and let the rope rewind into the starter at a controlled rate Figure 6 5 T1 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines 9 Give the starter a couple of test pulls to verify the right amount of tension on the st
85. ometer 18 Check the top no load speed of the engine NOTE The top no load speed of the engine is 3500 RPM s 100 NI 19 The top no load speed is easily adjusted by tighten h ing loosing the speed adjustment screw Tighten the Figure 4 35 screw to decrease speed and loosen it to increase speed See Figure 4 35 55 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines Fuel shut off valve To prevent the needle valve from un seating and flooding the engine while being towed engines designed to go onto log splitters have a fuel shut off valve built into the carburetor To service the shut off valve 1 Remove the carburetor by following the procedures described in Chapter 3 Air Intake Systems 2 Remove the choke lever pivot screw See Figure 4 36 Lift the choke lever off of the carburetor Remove the shut off valve cover using a 2 phillips screw driver See Figure 4 36 5 Remove the wave washer See Figure 4 37 56 Figure 4 36 v i a diy Cw ee i k g y E Nm r S x Es x pue i um LE Ww M cm Wave washer Figure 4 37 WWwW mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 FUEL SYSTEM AND GOVERNOR 6 Remove the fuel shut off lever See Figure 4 38 Figure 4 38 NOTE There is a passage cast into the shut off lever Fuel passage When this passage
86. on on summer engines NOTE Spark arrestors are an option that are required on all engines used in California and U S national parks See Figure 8 1 Inset The spark arrestor also serves to keep blockages out of the exhaust system NOTE Typical blockages include insect nests built during the dormant season The spark arrestor should be checked and or cleaned every month The spark arrestor can be inspected by shin ing a flash light into the muffler See Figure 8 1 If The spark arrestor needs to be cleaned or replaced 1 Remove the four screws that retain the muffler shield using a 10mm wrench and lift it off of the engine See Figure 8 2 2 Remove the spark arrestor retaining screw using a 2 phillips screwdriver See Figure 8 1 Pry the spark arrestor out of the muffler 4 The spark arrestor can be Replaced Cleaned by mechanical means e Solvent cleaned Burned clean using a butane or propane torch 5 Install the spark arrestor by following steps 1 3 in reverse order 91 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines Muffler removal replacement p ee 1 Remove the two nuts that hold the manifold pipe to Le the cylinder head using a 13mm wrench PEEN See Figure 8 3 a LY i x R 4 2 Lift the muffler off of the engine A Da NME 3 Clean all of the gasket material off of the cylinder head and the muffler See
87. one of the piston pin retaining rings See Figure 10 5 18 Remove the piston pin 19 Remove the piston rings from the piston using a pair of piston ring pliers See Figure 10 6 NOTE The piston rings and connecting rod are currently not available as service parts If they are damaged or worn the engine must be short blocked 20 Remove the crankshaft NOTE The crankshaft bearings are pressed onto the crankshaft and will come out with it 107 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines Crankshaft inspection 108 Inspect the crankshaft journals and the crank pin for galling scoring pitting or any other form of damage NOTE This is mostly a visual check Measurement is to determine if it is within the specifications after it is found to be OK visually NOTE The crankshaft and bearing are serviced as one assembly Measure the crank pin where the connecting rod attaches to the crankshaft using a vernier caliper or a micrometer See Figure 10 7 s A NOTE Micrometers are the preferred way to mea ES N ane sure the journals Measure the center and Pak A Bu the ends to check for tapering or egging Figure 10 7 Check the crankshaft for straightness by measuring the run out The crankshaft run out can be checked by 3a Place the crankshaft on a pair of matched V blocks or in the engine block with the sump installed 3b Place a dial indicato
88. ope and see if the spark goes away at the same time the engine dies 4 Engine over speed A Continual over speed e Binding or damaged external governor linkage or carburetor throttle e Mis adjusted governor arm e Internal governor failure B Momentary over speed Intermittent bind very unusual nterference This is fairly common when debris can fall on the governor linkage during normal operations 5 Engine RPMs surge hunting A Over governed condition Return spring replaced with wrong part or hooked into wrong hole NOTE This is an extremely rare condition usually created by tampering B Lean Air fuel mixture condition When AFR Air Fuel Ratio is significantly below stoichiometric ratio 14 7 1 engine RPMs sink until they reach a point that can be supported by the available fuel This Causes a momentary surge in power until the available fuel is consumed then the RPMs fall again repeating the cycle Too much air look for an air leak in the intake tract Not enough fuel look for fuel supply or carburetor problems 22 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 BASIC TROUBLESHOOTING Repairing the problem The third step in the troubleshooting process is to repair the problem This step consists of A Form a diagnosis by using all of the information gathered from the troubleshooting that was performed B Physically perform the repair The fourth and hopefully final step in the
89. overnor is unable to control the engine rpm the engine can accelerate past the safe maximum speed When an engine runs beyond its designed speed a few things happen 1 As the piston moves up and down in the cylinder it builds momentum The higher the rom s the more momen tum produced by the pistons As the momentum builds the connecting rods will start to stretch When the con necting rods stretch they get weaker Generally speaking this is at the narrowest part of the connecting rods On most engines that would be about an inch below the wrist pin but on the MTD engine it is at the wrist pin The force on the connecting rod is greatest when the piston transitions from the upward stroke to the down ward stroke Because of this most overspeed connecting rod failures will occur with the piston at top dead center When a connecting rod fails the piston stops moving but the crankshaft is still moving This will allow the bro ken connecting rod to get knocked around in the cylinder causing more damage to it Usually the connecting rod will be in several pieces after it breaks making it hard to find where the first failure was 2 All engines have vibrations and are designed to handle those vibrations but in overspeed the vibrations change resonance Parts that can not handle the new resonance will crack This may result in parts flying off of the engine which is an unsafe condition such as when a flywheel shatters pieces of it fly off of th
90. ow to customer Look for oil in the fuel Test the fuel for alcohol content if there is a reason to suspect it NOTE Save a sample of the fuel collected to show the customer NOTE Customers pouring engine oil into the fuel tank seems to be a growing problem 37 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines Test fuel for alcohol Fuels currently on the market contain a wide array of additives Some of these additives oxygenate the fuel Oxy genated fuel reduces emissions and is required in some parts of the United States Fuel make up varies seasonally and geographically Ethanol is the primary additive used to oxygenate fuel Ethanol in fuel creates a lot of problems for gasoline engines The biggest problem is that alcohol attracts and holds water This corrodes the metal components of the fuel system especially the carburetor Alcohol also does not produce as much heat as gasoline when burnt This results in less power for the engine A 10 ethanol E10 mix is acceptable for MTD engines Anything higher than that will result in performance issues NOTE E20 and E85 fuels are not to be used in any MTD engines There are several alcohol test kit available commer cially See Figure 4 1 LITT senses fal N dc d d ui To aa ir pe e Vu pay qD mn v Y gt ET Figure 4 1 Generally these kits involve mixing a measured amount of water
91. r at a smooth point at either end of the crank shaft 3c Slowly turn the crank shaft while watching the dial indicator NOTE Stop the crank shaft before the dial indicator hits the keyway 3d Compare the reading on the dial indicator to the specification listed at the end of this chapter 3e Repeat the above steps on the other end of the crank shaft www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 Crankshaft piston and connecting rod Piston Inspection 1 Clean the piston and remove all carbon from the rings and ring groves M f Clean the cylinder bore and remove all carbon pe iy g Insert one ring into the cylinder Push it down about P one inch from the top See Figure 10 8 Feeler gauge 4 Measure the end gap with a feeler gauge and com pare to the chart at the end of this chapter See Figure 10 8 5 Repeat steps 3 and 4 on the other rings NOTE Piston rings are not available as service parts If ia PU ev m any of the end gaps are out of spec the engine must be short blocked Lj Figure 10 8 Top piston ring h am ng E 6 Install rings back onto the piston NOTE The compression rings on the MTD engine have different profiles It is important that the proper pro filed ring is on the right grove See Figure 10 9 3 piece oil ring NOTE To help identify the top surface of the middle piston ring it has an H etched on it See Figure 10 1
92. r intake system for the snow and chore engines will be discussed separately as will the mufflers in a later chapter Heat box snow engines One of the big differences between snow engines and all other small engines is that the air intake of the snow engine does not have an air filter This is because air filters tend to freeze cutting off air flow to the engine The snow engine however does have a heat box to preheat the intake air The bottom of the heat box is open to draw in a large volume of cold air The top of the heat box has a small opening were the choke rod connects to the carburetor This draws in just enough warm air from the top of the engine to heat the cold air to the desired temperature as it enters the carburetor 2 emove Screws cm e A Figure 3 1 Hemove the bre ther hose T1 a S 4 5 Remove these Ca Figure 3 2 To remove replace the heat box Pull off the choke and throttle knobs Remove the control panel by taking off the five Screws secures it using a 10 mm wrench See Figure 3 1 Disconnect the wire from the ignition switch and the primer line from the primer button Slide the breather hose out of the heat box See Figure 3 2 Remove the two carburetor nuts using a 10 mm wrench See Figure 3 2 NOTE When installing tighten the carburetor nuts to a torque of 80 106 in lbs 9 12 Nm Remove the choke selector assembly Slide the heat box off of the ca
93. rburetor studs Install the heat box by following the previous steps in reverse order NOTE There is no gasket between the heat box and the carburetor 29 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines Air filter Summer engines Generally air filters come in two different types a F pleated paper element or foam A combination of the two x Paper pleated element are used on the MTD engine i e Air filters used on the MTD engine are designed to prevent particles larger than 3 5 micron from passing through into the engine e The filter should be checked on a regular basis possibly several times in a season NOTE Never use compressed air on a paper air fil ter Compressed air will remove the tiny fibers that are used to catch the dirt in the air Without these fibers the filter is useless NOTE Refer to Chapter 1 Introduction for the maintenance interval and cleaning instruc Foam pre filter tions for the air filter Figure 3 3 To replace an air filter E 1 Wipe down the air filter housing to prevent any a T ILLIC TIE i debris from getting into the engine b m P 2 Unthread the two wing nuts in the air filter cover Wings nuts See Figure 3 4 NOTE The wing nuts are part of the filter housing and do not come off 3 Swing the housing away from the fuel tank Air filter See Figure 3 5 housing
94. read here Loosen the nut and clamp bolt See Figure 4 42 n Carefully spread open the seam on the arm wr gg S D Carefully slide the Governor arm off of the governor shaft 6 Unhook the governor linage and throttle return spring To install the governor arm Figure 4 42 1 Rotate the governor shaft clockwise until it stops 2 Slide the arm onto the shaft The flat on the top of the shaft should be roughly parallel to the arm See Figure 4 42 NOTE There is a hairpin clip that keeps the governor shaft from sliding into the engine It may be necessary to hold the shaft while sliding the arm on to prevent the hairpin clip from popping off and allowing the governor shaft to fall into the engine Tighten the nut on the clamp bolt to secure the arm Attach the governor linkage and spring Adjust the governor to maintain top no load speed as described in a previous section of this chapter 58 WWwW mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 FUEL SYSTEM AND GOVERNOR Governor shaft To remove or replace the governor shaft 1 Remove the engine from the equipment that it pow ers 2 Remove the governor arm by following the previously described steps 3 Remove the flywheel by following the steps described in Chapter 7 Ignition Systems 4 Remove the crank case cover and crankshaft from the engine by following the steps described in Chap ter 10 Cam Crankshaft and Piston 5 Remove the ha
95. ression from the fuel system by preforming a prime test l Burns prime and dies This would indicate a fuel system issue Il Does not burn prime Not a fuel system issue Check for an ignition compression or flow problem 2c Compression or ignition problem Check the engine stop and safety switch ll Test the ignition system using a proper tester Ill Replace the spark plug with a new one or a known good one IV Check compression or leak down V Check valve lash 19 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines VI Check valve timing actuation VII Check exhaust 3 Starts runs poorly 3a Starts then dies Runthe engine with a spark tester in line between the spark plug wire and the spark plug or use an oscilloscope and see if the spark goes away at the same time the engine dies Il Check choke operation a Black smoke b Wet plug Ill Prime test immediately after engine dies If it restarts this may indicate a problem with fuel flow to the carburetor Check the gas cap fuel line fuel filter and the float in the carburetor 3b Runs with low power output Look for unusual exhaust color smoke Il Unusually hot muffler may glow red a Hetarded ignition b Exhaust valve opening early lash too tight Ill Mechanical bind a Aslightly bent crankshaft In some cases the drag may increase and decrease as the crankshaft rotates This pr
96. retor e Acap that maintains vacuum will cause the engine to run lean as the fuel is depleted and no air comes in to replace it e The two conditions may both be present but the symptoms vary with fuel fuel level and operating condi tions e A bad fuel cap vent usually presents as a Runs and quits scenario 39 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines The fuel filter The fuel filter is located in the fuel tank nipple It can be removed and cleaned with a can of carb cleaner or it can be replaced See Figure 4 4 NOTE If cleaning a filter back flush it by spraying the carb cleaner through the barb end and out of the screen Also make sure the fuel tank is clean Inset Fuel filter barb y A 4 kas Filter E i fr iml dE i E a NO 2 a Fo rE MEAG 14 SAE Sone BAN OV Figure 4 4 NOTE To replace the fuel filter follow the steps described in Chapter 1 Introduction Inspect the fuel lines e Are they cracked e Are they clogged e Are they brittle NOTE If the answer to any of the above is yes replace the fuel lines When replacing fuel lines low perme able fuel line must be used in order to meet EPA and CARB standards NOTE The nipple has a sharp edge that will damage the inner lining of the fuel line Replace the fuel line every time it is removed from the carburetor fuel nipple Aw
97. ring defects are wrongly blamed for a lot of failed parts A manufacturing defect is when a part is made wrong It could be a porous casting parts assembled wrong the wrong parts used or so on A manufacturing defect will generally show up within the first couple of hours of use Detonation preignition Detonation is the undesirable condition of the fuel spontaneously combusting the combustion chamber prior to the spark plug firing In this state the flame front from the detonation will start to travel through the combustion cham ber and a second flame front from the spark plug will crash into it The pressure differential caused by this will send shock waves through the engine The shock wave cause a knocking or pinging noise This is why detonation is sometimes called knocking spark knocking or pinging The shock wave will also try to push the piston down against the direction of rotation of the crankshaft The shock wave from detonation can cause piston failures melting or breakage piston skirt damage connect ing rod breakage and in extreme cases crankshaft failures A build up of carbon deposits in the combustion chamber will increase the compression ratio This is a major fac tor for the development of detonation It insulates the combustion chamber allowing it to heat up above normal oper ating temperatures Preignition is similar to detonation but on a smaller scale Preignition is cause by a localized hot spot or
98. round the valve cover opening clean the valve cover replace the valve cover gasket if nec essary Install the valve cover tightening the valve cover screws to a torque of 62 80 in Ibs 7 9 Nm IMPORTANT Over tightening the valve cover will cause it to leak Install the spark plug Cleaning the engine 1 To maintain a proper operating temperature and to keep the equipment looking good all debris should be removed from the engine It is recommended to use compressed air to blow all of the debris off of the engine NOTE A pressure washer may be used to clean outdoor power equipment but only after the unit has been allowed to properly cool NOTE Mice and other critters tend to build nests inside the engine shrouds while the snow blower is stored during the long off season 13 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines General torque specifications size M4 M5 M6 M8 size M10 M12 Grade 4 8 in Ibs 11 22 38 93 ft lbs 16 27 1 2 2 5 4 3 10 5 Nm 21 7 36 6 5 8 in Ibs 15 28 50 120 ft Ibs 20 35 1 7 3 2 5 7 13 6 Nm 2T 1 47 5 76 8 8 in Ibs 26 51 88 216 ft Ibs 35 61 97 2 9 5 8 9 9 24 4 Nm 47 5 82 7 132 10 9 in lbs 36 72 124 300 ft lbs 49 86 136 4 1 8 1 14 33 9 Nm 664 116 6 184 12 9 indbs 44 86 146 360 ft lbs 60 103 162 5 9 7 16 5 40 7 Nm 814 139 7 220 0 Noncritical inis 18 35 60 150 ft lbs Fasteners in Aluminum Nm Nm 339 Maintenance Chart
99. rts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines Insufficient lubrication The bearing surfaces in an engine are not smooth As a result of the machining processes to make the engine parts there are little peaks and valleys that are only visible on a microscopic scale These peaks are called asperi ties As the engine breaks in the asperities break off leaving plateaus that become the bearing surface The valleys become reservoirs for the lubricant When an engine is properly lubricated all of the moving parts glide on a thin film of oil If that film breaks down or carries enough grit to bridge the film damage will occur 1 When the parts are at rest they push the lubricant or oil away resting on the bearing surfaces As the parts rotate they climb over the oil pulling the oil between the bearing and the part riding on a film of oil The asperities are the first thing to make contact between two moving engine parts with an insufficient oil film between them This creates friction and causes a transfer of metal between the parts The heat and friction fur ther breaks down the oil film accelerating the process 2 Insufficient lubrication failures include e Low oil level e Wrong oil for the application e Contaminated oil e Degraded oil heat age acids 3 Metal transfer is the primary indicator that the film of oil between two engine parts has been violated If the damage is localized a general f
100. s rising See Figure 2 2 Figure 2 2 3 Interpreting compression readings Compression Readings Headings in psi Possible causes Most likely a stuck valve or too tight of a valve lash provided the starter rope pulls with normal effort Valve seat damage or pis ton ring and or cylinder wear 40 75 Normal readings 2 8 5 2 Bar 2 9 Excessive valve lash a 55 2 Bar partial hydraulic lock a bad cam or a bad automatic compression relief 26 WWwW mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 BASIC TROUBLESHOOTING PCV testing The PCV Positive Crankcase Ventilation valve is located in the valve cover and allows the crankcase pressure to escape Leakage and blockage are the two failure modes for a PCV system Either mode will cause crankcase pressure to build up though the effects of a blocked PCV are generally more dramatic Increased case pressure will result in oil entering the combustion chamber crankcase EE 1 The PCV chamber is vented to the heat box through a air chamber up BN molded rubber hose The rubber hose directs crank b case fumes to the heat box assembly See Figure 2 3 2 When functioning properly the PCV valve works with the inherent pumping action of the piston in the bore to expel pressure from the crankcase NOTE Normally small engines run with slightly negative case pressure This case pressure can be mea sured using a slack tube water manomet
101. shaft to verify full choke movement See Figure 4 23 3 If the choke plate does not open fully or close fully adjust the choke linkage NOTE When adjusting the choke linkage make small bends and recheck the movement of the choke plate Repeat this step until full movement is achieved Figure 4 23 4 Reassemble by following step 1 in reverse order 5 Testrun the engine before returning to service 49 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines Primers Snow engines MTD engines use a dry bulb primer This means that there is no fuel in the primer bulb The primer works by pushing air into the float chamber of the carburetor when the primer bulb is depressed This will force fuel to be sprayed out of the main nozzle into the throat of the carburetor To test the primer 1 Remove the engine shroud by following the steps described in Chapter 3 Air Intake Systems NOTE Do not disconnect the primer hose 2 Press the primer bulb while looking down the carburetor throat If there is fuel squirting into the carburetor throat the primer is working properly If not replace the primer and hose NOTE The primer and primer hose come as an assembly so there is no need to determine which part is bad To replace the primer 3 If the primer is bad disconnect hose from the carbu retor 4 Remove the hose camp at the rear of the primer bulb See Figure 4
102. shed versions Instructions photographs and illustrations used in this publication are for reference use only and may not depict actual model and component parts Copyright 2010 MTD Products Inc All Rights Reserved www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 Table of Contents Chapter 1 Introduction Professional Service Manual Intent llle 1 ode cre suas te barornet ether dd enscde sues eetstdon eeu a 1 FASENE 2ic4 es bee CIT d eet eo a hearers TT ILICE 3 Assembly INSIUCIONS 223 2 0 4 orna auk ead cad oon Ebr dh wa ads 3 Model and serial number llle 4 WIAIMENGNCE curs dra diei eoa iUd E oe eee RM I d fuc Scis 5 Air filter summer engines 0 eee 6 Oll type and capaci 5 4 xd door detuned pP Ra bexs dA ved eda 7 GHANGING IRE Ol METTRE 8 RU EEEE E T UTTPT 9 RUM Siren ait irae ee ee weenie ae Sea LEEREN 9 NACHOS ti PPP Ex 11 Cleaning THE NONE 9 9 6 9 ted Sheed Gd doh P RUD det C E Lok 13 General torque specifications llle 14 Maintenance Ghats pat ages deeded ee ERE Sa SEP Edad t 14 Frequently used specifications llle 15 Chapter 2 Basic Troubleshooting BIDS otras dS barber ea edu ORI E bce ee 17 HME OGUICUIONN EP 17 Steps to troubleshooting 0 ee eens 17 Define the problerm 5 22 nudo a e RE ere RE REIS 17 Identify factors t
103. stick that is completely covered with oil Figure 5 3 64 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 Lubrication Dip stick tube removal To remove replace the dip stick tube NOTE The procedure to remove the dip stick tube is the same for both styles of dip stick OMNE these TE s NOTE A threaded dip stick and tube assembly is inter changeable with a quarter turn dip stick and tube assembly 1 Remove the upper screw that secures the dip stick tube to the fuel tank support bracket using a 10 mm wrench See Figure 5 4 2 Remove the screw at the bottom of the dip stick tube using a 10 mm wrench See Figure 5 4 3 Pull the dip stick tube out of the engine block l 4 Inspect the O rings on the dip stick and the dip stick Figure 5 4 tube Replace if damaged NOTE Lubricate the O ringfor installation 5 Install by following the above steps in reverse order 65 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines Lubrication system MTD uses a splash lube system for its horizontal shaft engines The connecting rod has a dipper on it that splashes oil around the inside of the engine See Figure 5 5 NOTE The cam and the balance shaft were removed for a better view of the lubrication system The splashing action will create an oil mist that reaches the cylinder head There are two oil passages that r
104. ston metal shavings from the wear of engine parts or dirt enter ing through the oil fill port Leaking gaskets and seals also have the potential of allowing debris to enter the engine A symptom of abrasive ingestion is smoky exhaust As the cylinder walls wear pressure from the combustion chamber blows by the piston and pressurizes the engine sump This overpowers the PCV valve and allows oil to build up in the combustion chamber See Figure 11 3 Figure 11 3 T Abrasive materials that enter the engine get absorbed by the oil and thickens it See Figure 11 4 Figure 11 4 122 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 Failure Analysis 8 Because the oil suspends the abrasive particles the engine components that are immersed in oil will show definite signs of abrasive ingestion especially around the connecting rod and main bearing journals See Figure 11 5 NOTE Abrasives that are trapped in the oil will cause the lower portion of the combustion chamber to wear ing more than the upper portion NOTE Wear of only one bearing surface on a new engine could be a sign of a manufacturing defect Figure 11 5 NOTE Abrasive particles can also be embedded into materials that are softer than the abrasive This will cause the affected part to act like a piece of sand paper or a grinding wheel See Figure 11 6 Embedded abrasives Figure 11 6 123 www mymowerparts com For Pa
105. sts of a multitude of individual hydrocarbons and has a boiling range of 86 410 F 30 210 C The large quantity of hydrocarbons and the low boiling range makes gasoline an ideal fuel for spark ignited internal combustion engines However the hydrocarbons are not good for the environment To reduce or eliminate the release of fuel vapors into the atmosphere an evaporative EVAP emissions system is used Effective January 1 2011 the EPA has mandated that all summer engines with 225cc s of displacement or more must be equipped with an evaporative emissions system The EVAP system used by MTD consists of A charcoal canister Roll over valv i The fuel tank and cap Charcoal canister NN A roll over valve vent i The control panel Vacuum lines Heference 1 Dr Ullmann J Fuels Automotive Handbook seventh edition Bosch Robert distributed by SAE Society of Automotive Engineers 2007 320 42 WWwW mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 FUEL SYSTEM AND GOVERNOR This system operates as follows Was a 4 e ENS 1 The gasoline evaporate and lets off vapors E 4 d e 2 The vapors exit the fuel tank through the roll over valve vent NOTE The fuel cap used with the charcoal canister sys tem is not vented If a vented cap is used the EVAP system will not work See Figure 4 9 NOTE The new EPA standard also requires the fuel caps to be tethered to the
106. t See Figure 9 13 e Valve seats are 45 degrees with a 31 degree topping cut and a 61 degree narrowing cut e Seat width should be 0 028 0 035 0 7 0 9mm with a margin of 0 024 0 6mm on the exhaust valve and 0 027 0 7mm on the intake valve 0 028 0 035 NOTE The valve seat can be ground to clean it up as long as the finished seat is within the tol erances listed above eat angle is 45 i margin Seat A LEE contact Figure 9 13 Inspect the valve stem See Figure 9 14 Inspect the valve springs NOTE Valve spring free length should be at least 1 22 28 5mm Original length is 1 44 36 6mm Install the valves in the cylinder head by following steps 2 5 in reverse order F CC l0oN eC Inspect for a 45 burnt edge Figure 9 14 www mymowerparts com 12 13 For Parts Call 606 678 9623 or 606 561 4983 Cylinder head Test the valves for leaks by 10a Place the cylinder head on a couple of wood blocks with the valves facing up 10b Pour a small amount of gasoline or parts cleaning solvent into the combustion chamber just enough to cover the valves 10c Let the cylinder head sit for ten minutes 10d Check for gasoline leaking out of the intake and exhaust ports Install the cylinder head by following the steps described earlier in this chapter oet the valve lash by following the steps described in Chapter 1 Introduction Test run the engine in a saf
107. t using a 10mm wrench See Figure 4 27 NOTE From this point an assessment can be made about the viability of rebuilding the carbure tor e f extensive corrosion is evident replace the carburetor e If varnish build up is too extensive to clean replace the carburetor Figure 4 25 7 When inverted the float should rest in a level posi tion See Figure 4 26 Figure 4 26 52 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 FUEL SYSTEM AND GOVERNOR Float bowl 8 Remove the pin that the float hinges on to remove Drain bolt the float NOTE The float is not adjustable Spring tension against the float valve begins to build from the horizontal position putting progressively more pressure between the tip of the valve and the seat Flat fiber See Figure 4 28 gasket A X Bowl bolt with recess in 7 head for O ring E Gasket seal Figure 4 27 NOTE Because the float valve is crucial to the functioning 4 Float of the carburetor and the viton tip of the valve is subject to wear technicians should replace the valve and spring any time the carburetor is disas Float valve sembled for cleaning e A square cross section gasket seals the bowl to the body of the carburetor _ Compression gd spring mae M EN Figure 4 28 d Main jet 9 Remove the main jet using a narrow shank straight blade screwdriver See Figure 4 29 NOTE Fuel enters the central colu
108. test A leak down test is the preferred method to test the engine s ability to compress the charge It will also show where pressure is leaking from To perform a leak down test NOTE A leak down test pressurizes the combustion chamber with an external air source and will allow the technician to listen for air leaking at the valves piston rings and the head gasket NOTE These are general instructions Read and follow the instructions that came with the tester before attempting to perform this test e f possible run the engine for 3 5 minutes to warm up the engine e Remove the spark plug and air filter e Find top dead center of the compression stroke If the engine is not centered at top dead center the engine will rotate when compressed air is introduce to the combustion chamber 1 Find top dead center by following the steps described in the valve lash section of Chapter 1 Introduction 2 Thread the leak down tester adapter into the spark plug hole See Figure 2 1 Connect tester to compressed air Adjust the regulator knob until the needle on the gauge is in the yellow or set area of the gauge 5 Connect the tester to the adapter ES Leak dow NOTE If the engine rotates it was not at top dead tester center E 6 Check the reading on the gauge EM Figure 2 1 24 WWwW mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 BASIC TROUBLESHOOTING 7 Compare the results to the following
109. the text that covers assembly They may be summa rized in tables along with special instructions regarding locking or lubrication Whichever method is more appropriate will be used In many cases both will be used so that the manual is handy as a quick refer ence guide as well as a step by step procedure guide that does not require the user to hunt for informa tion Lubricant quantity and specification may be noted in the part of the text that covers maintenance and again in the section that covers assembly They may also be summarized in tables along with special instructions Whichever method is more appropriate will be used In many cases the information will be found in several places in the manual so that the manual is handy as a quick reference guide as well as a step by step procedure guide that does not require the user to hunt for information The level of assembly instructions provided will be determined by the complexity of reassembly and by the potential for damage or unsafe conditions to arise from mistakes made in assembly some instructions may refer to other parts of the manual for subsidiary procedures This avoids repeating the same procedure two or three times in the manual www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines Model and serial number The model and serial number can be found on a white sticker with a bar code The sticker is located on the ri
110. trodes cracked insulator metal transfer deposits may indicate detonation e A Spark plug that is wet with fuel indicates that fuel is present in the combustion chamber but it is not being ignited Spark plug removal 13 16 spark plug socket p 1 Disconnect and ground the spark plug wire Tie 2 Remove the spark plug using a 13 16 or 21mm wrench A flexible coupling or wobbly extension may help See Figure 7 15 3 Gap anew spark plug to 0 026 0 030 0 65 0 75 mm Muffler 4 Install the new spark plug and tighten to a torque of 15 18 ft lbs 20 25 Nm Valve cover due ese Figure 7 15 89 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines 90 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 Exhaust CHAPTER 8 EXHAUST The exhaust system is a frequently overlooked component of an engine It is important to make sure the muffler is in good condition and free of debris and or insects NOTE A blocked muffler will result in poor performance If a muffler is completely blocked the engine may not Start Summer engines One of the main differences between the summer and the snow engines is the exhaust system Because of this they will be addressed separately Spark arrestor if equipped ro CORAN E T Spark arrester Figure 8 2 A spark arrestor is available as an opti
111. troubleshooting process is the follow through This step consists of A Thoroughly test the repaired equipment confirming that the initial diagnosis was correct If it was wrong start the troubleshooting process over again NOTE Sometimes the engine will have multiple problems at the same time By performing one repair other issues may show up that are unrelated to the first repair B Delivery to customer We are not just repairing equipment we are repairing customers Inoculate against recurring problem with education e g if the problem was caused by stale fuel make sure the customer is aware that fuel goes bad over time Make sure the customer understands the repair preventing Superstitious come backs 23 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines Prime test To perform a prime test 1 Prime the engine through the carburetor throat using a squirt bottle filled with clean fresh gasoline 2 Make sure the throttle is in the run position and the safety key if fully inserted 3 Attempt to start the engine 4 If the engine starts and runs long enough to burn the prime the problem is effectively isolated to the fuel sys tem proceed to Chapter 4 The Fuel System and Governor e Check ignition system as described in Chapter 7 Ignition System If the ignition system is working check the compression or perform a leak down test Leak down
112. ts it is probably more economical to replace the cylinder head versus servicing the valves Press down and slide off fue Ue Fe Syy Ec WM EL a Secondary valve keeper ual Figure 9 11 To service the valves NOTE Servicing valves during the warranty period will void the warranty Warranty valve repairs are to be accomplished by replacing the cylinder head 1 Remove the cylinder head by following the steps described earlier in this chapter 2 Remove the rocker arms by 2a Remove the jam nuts 2b Remove the fulcrum nut 2c Slide the rocker arms off of the rocker studs 3 Remove the valve retainers by applying light finger pressure and moving the retainer so that the valve stem passes through the large part of the keyhole opening in the retainer See Figure 9 10 NOTE The valve keepers are not interchangeable NOTE The exhaust valve has a cap called an adjuster on it The cap needs to be pulled off before the keeper can be removed See Figure 9 11 NOTE If the engine has a dropped valve remove the cyl inder head inspect the valve and the piston for damage 101 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines Lift the springs off of the valve stems Slide the valves out of the cylinder head NOTE Only the intake valve has a valve guide seal See Figure 9 12 Figure 9 12 Inspect the valve sea
113. un along the engine cylinder The one on the top side of the engine is the oil supply passage The oil mist will flow through this passage to the cylinder head See Figure 5 6 The second oil passage runs along the bottom side of the cylinder This is the oil return passage As the name implies it allows the oil collecting in the cylinder head to return to the sump The return passage is the tiny hole that is in between the two tappet passages NOTE Because these engines use splash lubrica tion the type of oil and the oil level is critical for proper operation of the engine If the oil level is too low the dipper on the connecting rod cannot splash the oil into the engine If the oil level is too high the oil will not change into a mist to reach the upper side of the engine E i 1 ros 4 f P s 2 st L Y 4 T L P d z j i P n d Er E De j Y F r i I J j J Figure 5 6 66 WWwW mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 Positive crankcase ventilation valve y Rem ay amp Breather hose ove these yay Figure 5 8 Lubrication To remove the valve cover and PCV valve NOTE The PCV valve is located inside the valve cover The function and test procedures for the PCV valve is covered in Chapter 2 Basic Troubleshoot ing 1 Disconnect and ground the spark plug wire 2 Squeeze the spring clamp that secures the breather hose to the valve cover
114. un the engine before returning to service 88 WWwW mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 Ignition System About the spark plug e The spark plug is a FERTC gapped to 0 026 0 030 0 65 0 75 mm NOTE The F6RTC plug is the only plug that is EPA certified for the MTD engine e Wear rate will vary somewhat with severity of use If the edges of the center electrode are rounded off or any other apparent wear damage occurs replace the spark plug before operating failure no start occurs Cleaning the spark plug e Cleaning the spark plug is not recommended If the plug needs to be cleaned replace it e Use of a wire brush may leave metal deposits on the insulator that cause the spark plug to short out and fail to spark e Use of abrasive blast for cleaning may damage the ceramic insulator or leave blast media in the recesses of the spark plug When the media comes loose during engine operation severe and non warrantable engine damage may result Inspection of the spark plug Inspection of the spark plug can provide indications of the operating condition of the engine e Light tan colored deposits on insulator and electrodes is normal e Dry black deposits on the insulator and electrodes indicate an over rich fuel air mixture too much fuel or not enough air e Wet black deposits on the insulator and electrodes indicate the presence of oil in the combustion cham ber e Heat damaged melted elec
115. ver heated engine Figure 11 10 126 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 Failure Analysis Mechanical Breakage Wear Sometimes an engine fails because a part breaks There are generally three causes of a broken part outside of the previously discussed engine failures They are abuse wear and manufacturing defects A very common way to abuse an engine is a bent crank shaft Crank shafts bend when they or something bolted to them hits something A prime example of this is when a mower blade hits a rock See Figure 11 11 As the engine runs there is friction between the mov ing parts This friction wears down the parts Lubrication slows the process but wear can not be prevented Over time the parts wear to the point they break or fail in some way Car tires are a good example of wear A tire will only last for so many miles before all the rubber is worn off and the tire goes flat Bushings are another example they are Figure 11 11 designed to wear so that the wear of other parts will be minimized Vibration issues have a chicken and the egg relationship to mechanical failures Which came first Bent crank shafts and imbalanced implements will cause vibration issues However a vibration issue such as a over speed or loose mounting bolts on the engine can shake an engine to pieces The technician must find the source of the vibra tion in order to properly diagnosis an engine Manufactu
116. x obviously dangerous conditions as soon as they are noticed Lift and support heavy objects safely and securely Be aware of your surroundings and potential hazards that are inherent to all power equipment All the labels in the world cannot protect a technician from an instant of carelessness Exhaust fumes from running engines contain carbon monoxide CO Carbon monoxide is a colorless odorless gas that is fatal if inhaled in sufficient quantity Only run engines in well ventilated areas If running engines indoors use an exhaust evacuation system with adequate make up air ventilated into the shop www mymowerparts com Fasteners For Parts Call 606 678 9623 or 606 561 4983 Introduction Most of the fasteners used on the MTD engine are metric Some are fractional inches For this reason wrench sizes are frequently identified in the text and measurements are given in U S and metric scales If a fastener has a locking feature that has worn replace the fastener or apply a small amount of releas able thread locking compound such as Loctite amp 242 blue Some fasteners like cotter pins are single use items that are not to be reused Other fasteners such as lock washers retaining rings and internal cotter pins hairpin clips may be reused if they do not show signs of wear or damage This manual leaves that decision to the judgement of the technician Assembly instructions Torque specifications may be noted in the part of
117. y leave tracking marks were the particles enter the sys tem Use these marks to find the source of the abra sives 3 Particles that enter the intake system travel at great speed and act like sand blasting media inside the engine This causes wear to the parts affected 4 The particles can pass through the intake system to the valves and valve seats Figure 11 1 121 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 78 83 90 Series Horizontal Shaft Engines D When particles enter the combustion chamber the up and down motion of the piston grinds the parti cles into the side of the cylinder walls and damages the cylinder wall piston and piston rings 6 This can be identified by the scoring along the verti cal axis of the piston and cylinder wall or the cross hatch on the cylinder wall being worn off NOTE To help in the lubrication of the cylinder walls and help with the seating of the piston rings a diamond cross hatch is honed into the cylinder wall Debris entering the cylinder will polish the cross hatch off of the cylinder wall See Figure 11 2 NOTE Abrasives that enter the engine through the Figure 11 2 intake system will cause the upper portion of the combustion chamber to wear more than the lower portion Measurements of the cylinder bore at the top and bottom will show this Other sources of abrasives that get into the engine includes carbon that builds up on the top side of the pi
118. zontal Shaft Engines 80 www mymowerparts com For Parts Call 606 678 9623 or 606 561 4983 Ignition System CHAPTER 7 IGNITION SYSTEM Troubleshooting the ignition system The purpose of the ignition system is to provide a spark in the combustion chamber at the proper time to efficiently ignite the fuel air mixture The steps in troubleshooting the ignition system are 1 Examine the spark plug s by following the steps described in the spark plug section of this chapter NOTE It is convenient to check the compression when the spark plug is removed for examination 2 Connect a spark tester between the spark plug wire and a good ground point on the engine See Figure 7 1 Never remove the spark plug and VAcaurion hold it against the cylinder head to test for spark The fuel air mix com Spark tester Figure 7 1 ing out of the spark plug hole will catch on fire NOTE It only takes 1 000 volts to jump a 0 025 air gap in open atmosphere it takes 10 000 volts to jump the same gap at 120 psi therefore an open air spark test in not valid NOTE The spark should be a minimum of 10 Kv 10 000 volts at pull over speed Make sure any remote stop switch is turned to the run position 4 Pull the starter rope If sparks can be seen in the spark tester the ignition system is working NOTE If there are sparks present in the spark tester install a known good spark plug and prime test the engine If the engine

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