Basic Service Procedures and Principles of Operation for the KM 56
Contents
1. STIHL Inc Virginia Beach VA 2014 Piston Ported Stratified Scavenging Intake Compression Stroke STIFIL Fresh air fuel mix from the carb enters the low pressure in the crankcase through the intake port 1 Clean air enters through the bypass ports 2 he control recess 4 in the piston skirt routes the air into the top of the transfer ports 3 s he air travels down the transfer ports 3 towards the crankcase STIHL Inc Virginia Beach VA 2014 Piston Ported Stratified Scavenging o Power Stroke Transfer Port Loading STAL As the piston moves down the fresh air is trapped in the transfer ports he piston Is coming down on the power stroke he underside of the piston Is pressurizing the air fuel mix in the crankcase LON WD C E i E STIHL Inc Virginia Beach VA 2014 Piston Ported Stratified Scavenging Scavenging Exhaust Stroke As the piston opens the transfer ports the fresh air comes in first The air scavenges out the exhaust gases The air fuel mix IS delayed from entering the combustion chamber for a fraction of a second STIHL Inc Virginia Beach VA 2014 STAL Piston Ported Stratified Scavenging STIHL Transfer and Scavenging he fresh air is now pushed by the air fuel mix to continue the exhaust scavenging process he piston now comes2. Piston comes up and compresses the air fuel mix Spark plug ignites the air fuel mix and expanding gases push the piston down on the power stroke r peaa STIHL Inc Virginia Beach VA 2014 Two Stroke Piston Port STIHL Inc Virginia Beach VA 2014 Scavenge Loss STIHL Notice that the blue incoming air fuel mix sweeps through the combustion chamber and helps push the exhaust gases out through the open exhaust port d tis the nature of a typical two stroke 4 ct piston port engine design that some of the air fuel mix that transfers Into the combustion chamber leaks out the open exhaust port his is called scavenge loss of unburned fuel and is the primary reason that two stroke engines have poorer fuel economy and higher emissions than a four stroke engine STIHL Inc Virginia Beach VA 2014 STAL KM 56 RC E Stratified Scavenge Engine Design Astratified scavenge two stroke piston port engine operates by Introducing a puff of clean filtered air between the exhaust gases and the incoming air fuel mix he air is routed into the transfer ports from the top down and stacks up there until it is released into the combustion chamber he small amount of air holds the air fuel mix back for a fraction of a second to give the piston time to move up and close the exhaust port his creates an increase in fuel economy and a decrease in unburned hydro carbon emissions
3. Chain brake actuates properly C Throttle interlock works properly C Sooted over C Normal in appearance Spark plug gap C Pressure test crankcase to specifications and record results If values do not meet specifications locate C Set Idle RPM to L Verify WOT RPM to Choke operates properly L Engine idle RPM change excessive at roll out Other observations Other observations leaks and note results required to move ahead and back to get all the steps done _ Acceleration response OK L Run under load satisfactory Chain oiler working C Line advance operation OK Comments On Four Stroke re install valve cover for above AV system condition 14 Muffler condition Spark arrester screen blocked or missing 27 Crankshaft end play excessive Starter rope worn frayed length amp C Crankshaft side play excessive diameter OK Other observations 28 Carb Check Air Filter worn or damaged C Physical damage Throttle shaft condition 15 Four Stroke Only Air Filter packed with dirt or debris Valve clearance OK Leak Down Test 96 of leakage refer to the Carburetor Quick Check If over 10 location of leakage Other observations Worksheets for detailed carb analysis 5 Copyright 2009 STIHL Incorporated Virginia Baach VA Purge Primer Carb All rights reserved L Step 1 Pressure test carb inlet no higher STIHL dealers may copy this document for their us
4. Tank STAL a f the tank is empty look down in the tank to see if it appears contaminated with debris or anything else that shouldn t be there f the unit has fuel in it carefully remove the cap and wave your hand over the opening while smelling for a sour odor that may indicate old stale fuel Pour the fuel out in a pan and see if there Is trash or debris or any evidence of other contaminants such as water in the fuel p en 5 20 T i i STIHL Inc Virginia Beach VA 2014 20 Fuel Filter Use the 5910 893 8800 hook tool to fish the fuel filter out of the tank for inspection Carefully remove the top of the filter and slide the sintered plastic element out The filter body screen should be clear and in good condition and the element may have oil staining but should not be dark or fouled or have any kind of coating on it STIHL Inc Virginia Beach VA 2014 Pressure Vacuum Tester 0000 850 1300 Pump With the knurled ring to the right the gauge indicates pressure With the knurled ring to the left the gauge indicates vacuum STIHL Inc Virginia Beach VA 2014 Hose Removal The 5910 890 4501 tool works well to remove fuel impulse or vent hoses Use a side to side rocking motion while pushing against the hose to walk it off of the fitting STIHL Inc Virginia Beach VA 2014 21 Pressure Test Fuel Line Connect the pressure tester to
5. and will be at a fast idle A ize Activate the throttle and the Y engine will return to idle STIHL Inc Virginia Beach VA 2014 STIHL Fault Analysis STIHL Engine Check When a unit is running poorly or not at all using a systematic approach to identify any and all faults present will allow the Service Technician to quickly and efficiently determine what is wrong a tis just as important to know what faults are not present as well as faults that do need to be addressed his document is for use on all handheld CERRMASE BRI products so some of the steps do not apply and in some cases the 17 _ Cooling fins blocked cracked broken off C Step 2 With pressure present from step 1 pump the primer bulb and the pressure should drop if it does use a vacuum gauge hooked to the inlet fitting and pump the primer until a vacuum is indicated on the gauge and it must hold for 1 full second minimum if not the carb has an internal air leak C Step 3 Connect a pressure gauge to the outlet fitting and pump the primer pressure should build and hold if not the purge primer flange is faulty 18 7 Magneto air gap correct 19 Fuel have a stale odor C Debris or water in tank C Color of fuel Other observations 20 Fuel Filter appear dirty or restricted Non Purge Carb Pressure test carb inlet no higher than 10PSI if it holds then the fuel pump components and inlet needle
6. readable replace as needed If this label is damaged or worn away a universal replacement label is available from STIHL Yellow Power Tool Label 0000 967 3541 STIHL Inc Virginia Beach VA 2014 3 Cutting Attachment 4 Belt Tension For this KM 56 RC these do not apply so just draw a line through them and continue to the next item STIHL Inc Virginia Beach VA 2014 5 Operator Controls Be sure the throttle trigger and throttle interlock works freely Verify the stop switch when pushed to the O position and released it springs back to the run position Rotate the choke knob to the full on position and then squeeze the throttle trigger and the choke knob should automatically return to the run position STIHL Inc Virginia Beach VA 2014 6 Verify Anti vibration Components Most STIHL chain saws and line trimmers have a anti vibration system that should be inspected for wear and damage The KM 56 RC E does have an anti vibration system so continue to next item STIHL Inc Virginia Beach VA 2014 7 Inspect Starter System Inspect rope handle and eyelet for wear or damage Pull the rope to it s full extended length and be sure it is not about to break at the very end P RE it _ E em a im onse m n cm ect t me Gee P nnd e f Zs _ LLLE STIHL Inc Virgin
7. Basic Service Procedures and Principles of Operation for the KM 56 RC E KombiMotor STIHL STIHL Inc Virginia Beach VA 2014 Introduction STIHL The KM 56 RC E is a 2 cycle stratified scavenge engine The stratified scavenge engine design is more fuel efficient using about 20 less fuel than previous models with similar displacement his engine design is very effective at reducing exhaust emissions STIHL Inc Virginia Beach VA 2014 Specifications Engine Displacement 27 2 cc 1 66 cu In Engine Power 0 8 kW 1 1 bhp Weight 4 3 kg 9 5 Ibs Fuel Capacity 340 cc 11 5 oz 2500 RPM Engine Idle Speed Maximum Engine Speed 10000 RPM A AE LL ee e P Md w NRA box h e e n aN A E TW T v x y 1 remm J Bw D s HELLE llli STIHL Inc Virginia Beach VA 2014 STAL Two Stroke Piston Port Engine Design 1 Combustion Chamber A conventional two stroke piston port engine operates by mn E E u Piston moves up and creates a 4 intake Pon vacuum in the crankcase which 5 Crankcase E E E draws air fuel oil mix in from the 6 Crankshaft carb 7 Transfer Port 8 Spark Plug Piston skirt comes down and blocks the intake port and creates pressure in the crankcase Piston continues down and pushes air fuel oil mix through the transfer ports and into the combustion chamber which helps push the exhaust gases out the exhaust port
8. appear to be carburetor related For the KM 56 RC E the impulse signal 7 E comes out through the flange here STIHL Inc Virginia Beach VA 2014 25 Impulse Signal Present Place a small amount of grease over the impulse port on the flange just enough to cover it STIHL Inc Virginia Beach VA 2014 25 Impulse Signal Present Now watch the port carefully and spin the flywheel back and forth by hand and the grease should be either drawn in or pushed out verifying that there is an Impulse signal from the crankcase to the carb STIHL Inc Virginia Beach VA 2014 26 Vacuum and Pressure Test of Crankcase A two stroke engine typically must have an air tight or nearly so crankcase since the air fuel mix Is coming through the crankcase on the way to the combustion chamber This test verifies that there are no pressure leaks at places like gaskets or HIV silicone sealed mating surfaces and that the crankshaft seals are not leaking under pressure or vacuum Block off the exhaust port by starting the muffler screws in place and slipping a rubber block off plate in between the muffler and the cylinder then snug up STIHL Inc Virginia Beach VA 2014 26 Vacuum and Pressure Test of Crankcase Install the correct adapter flange in place of the carb a The Service Manual for each model describes how to do this test and gives the part number for the adapter amp For the KM 56 RC E the part number
9. are sealing if it leaks indicate where the leak is Detailed Fault Analysis 1 C Deflectors shrouds covers Filter torn or damaged 10 Carburetor Screw Settings Other observations Limiter Caps Present if equipped Verify settings if caps are missing or unit does not use limiter caps ONE GRE H L 21 Pressure test fuel line 0 8 bar C Fasteners loose or missing C Verify main nozzle check valve and accelerator pump if equipped by doing a vacuum test 23 Vacuum test tank vent All carbs C Condition of fuel inlet screen 24 Remove carb inspect intake side of piston C Condition of diaphragms stiff damaged condition OO HR evidence of contamination 22 Pressure test tank for leaks Warning Labels 11 _ Spark plug connection terminal spring and high tension lead condition C Cutting Attachment Note type amp condition any accessories present 12 Spark present with STIHL ZAT4 tester No install new plug and retest Other observations J Ignition shut off function Belt tension and condition TS 25 Impulse passage clear 29 Any other observations about unit 26 Vacuum test crankcase to specifications Final Running and record results CO Unit starts easily Check Specification Chart for RPM settings C Throttle operates smoothly 13 Spark plug correct heat range L Multi Function lever works smoothly C Spark plug carbon fouled technician may be _
10. back up and closes the exhaust port his minimizes the scavenge loss of unburned hydro carbons out the open exhaust port STIHL Inc Virginia Beach VA 2014 KM 56 RC E Stratified Scavenge Design Air Fuel Mix From Carb Enters Flange Here ocavenge Air From Carb Exits Flange Here oleeved Cylinder with closed transfer ports ocavenge Air From Carb Enters Flange Here Air Fuel Mix From Carb Exits Flange Here STIHL Inc Virginia Beach VA 2014 New Split Carb Design for Stratified Scavenging STAL KM 56 RC E carb design main nozzle rich air stream lean alr gt stream venturi Spacer throttle plate carb body flange STIHL Inc Virginia Beach VA 2014 KM 56 RC E Operating Features Reading and becoming familiar with the instruction manual is the first step to learning about the blower it s features and how to operate it safely STIHL KM 56 R P Starting and general operation and r maintenance is explained STIHL Inc Virginia Beach VA 2014 STIHL WARMING Function of the Stop Switch The stop switch has a spring loaded rocker style action and is normally in the run position Rock the switch to the O or off position to stop the engine The switch does not have to be held in the O position just pushed down and released The ignition module resets itself automatically to the run position after the flywheel stops turni
11. e only than 10PSI if it holds then the fuel pump ae 5 components and inlet needle are sealing and go to step 2 if it leaks indicate where the leak is 16 Two Stroke Only Remove Muffler C Carbon deposits in exhaust port L Piston condition _ Piston rings free C Cylinder wall condition Other observations L Dirt or debris on clean side of filter _ Evidence of dirt in carburetor bore or on choke butterfly Other observations STIHL Inc Virginia Beach VA 2014 DG Screws STIHL uses these type of fasteners in manufacturing because they cut their own threads the first time they are used Notice that the ones holding into plastic have a different pitch and profile than the ones that hold into metal It is imperative that the Service Technician keep track of which screw is which and not screw them into the wrong base material or the threads will be damaged It is also best practice that when starting a DG screw into the hole slowly rotate it backwards until it clicks to index the threads then turn it clockwise to tighten it STIHL Inc Virginia Beach VA 2014 1 Deflectors Shrouds Covers Fasteners Visually look the unit over for damage missing items loose fasteners or anything else that is obvious Damaged shroud may be a safety hazard for the operator D an air filter or cover STIHL Inc Virginia Beach VA 2014 2 Warning Labels Verify that labels are present and
12. ia Beach VA 2014 8 Inspect Air Filter Remove the air filter cover to expose the air filter Gently pry out the filter for Inspection STIHL Inc Virginia Beach VA 2014 9 Inspect Air Filter Housing STIL The black plastic baffle directs and A ba SW m y accelerates the clean air into the carburetor E s Remove the baffle and check behind it and down into the throat of the carburetor he clean side of the filter should not have any dirt or debris present m f there is dirt on the clean side indicate this as a dirt ingestion fault and the cause must be identified Dirty operating conditions require filter maintenance Verify that the cover filter or filter housing are not damaged allowing dirt to leak in around the filter STIHL Inc Virginia Beach VA 2014 10 Carburetor Mixture Screws amp All current STIHL products will be equipped with either limiter caps or tamper resistance screws on the H and L mixture screws his unit requires a special thin wall y socket screwdriver to adjust the v mixture screws his is a special tool and is not available to the consumer The basic settings for this carb is H 1 1 2 turns open L 1 turn open STIHL Inc Virginia Beach VA 2014 11 Spark Plug Connection Use a twisting motion to remove the spark plug connection and be careful not to pull the clip out of the high tension lead I
13. is 5910 850 4200 Be sure the gasket is in good condition and in place Be sure the spark plug is installed and tight STIHL Inc Virginia Beach VA 2014 26 Vacuum and Pressure Test of Crankcase Connect the pressure vacuum tester to the fitting on the flange and pull a 0 5 bar vacuum and it should hold steady or not leak back to 0 3 bar within 20 seconds Always rotate the crankshaft back and forth while the crankcase is under vacuum to verify that the seals are holding properly Switch the tester to the pressure mode and pump 0 5 bar of pressure into the engine and it should hold steady for at least 20 seconds STIHL Inc Virginia Beach VA 2014 Pressure Vacuum Test Results This test verifies that there are no internal air leaks anywhere in the engine If the unit fails the pressure test always check the obvious things first such as the rubber sealing plate on the ex and the adapter on the intake side as well as the spark plug by spraying with soapy water and looking for bubbles If they are sealing properly then the engine may need to be taken apart far enough to be able to check the crankshaft seals and the seal between the cylinder and the crankcase If an engine leaks under vacuum but holds under pressure it is most likely a crankshaft seal STIHL Inc Virginia Beach VA 2014 27 Crankshaft and Bearing Condition oee if the crankshaft moves in and out or up and down There should not be any loose
14. ng WARNING When service work is performed always disconnect the Spark plug terminal Remove the spark plug terminal with a twisting motion STIHL Inc Virginia Beach VA 2014 Starting the KM 56 RC E Fill the tank with 89 octane brand name fuel with STIHL two stroke oil mixed at a 50 1 ratio Pump the purge primer bulb until it fills with fuel at least five times Push in the choke knob and rotate upward and it locks in the cold start position Hold the unit against the ground with the right hand on the handle Pull the rope through until the engine starts usually within one to two pulls STIHL Inc Virginia Beach VA 2014 Starting the KM 56 RC E Once the engine starts it will stay running but the choke is still in the ON position Activate the throttle trigger slightly and the choke will release automatically and the engine will drop down to idle he choke also locks in the middle warm start postion he choke always releases automatically when the throttle trigger is activated Allow the engine to idle for at least 1 2 a minute to warm up A cold engine may not accelerate smoothly until it is warmed up STIHL Inc Virginia Beach VA 2014 Warm Starting the KM 56 RC E a f the engine has been running and then is stopped for a short time always set the choke control to the middle position n ee A Wu a Ww Mx Ww The engine should start on the first pull
15. nspect it for damage hardness or cracks TUITEEER Ge c de A W zn c gt 4 EE M 594 NAN Mein b 2 SAM SVP ar STIHL Inc Virginia Beach VA 2014 12 Spark Test Connect a ZAT 4 or equivalent in line spark tester and pull the rope through as if trying to start the engine A bright orange light indicates the ignition Is firing the spark plug If no spark is present try again with a new plug A fouled or defective spark plug may not show spark on the tester even If the ignition system is OK STIHL Inc Virginia Beach VA 2014 12 Ignition Shut Off Function If spark is present then hold the stop switch in the off position and pull the rope through and verify that no spark is present This verifies that the stop switch and connecting wiring Is in order STIHL Inc Virginia Beach VA 2014 13 Spark Plug Hemove the plug and verify that is the correct plug For a KM 56 RC E the correct plug is a NGK CMR6H part number 0000 400 701 1 If another brand of plug is installed or used use a cross reference chart to be sure it has the same heat range as the NGK CMR6H A P Z s P i is Normal tan color normal EE 2 electrode wear es E amp due to high run time Plug has M served its m useful life A STIHL Inc Virginia Beach VA 2014 14 Muffler Remove the top engine housing Remove the spark arrester screen and inspect it
16. play in the crankshaft bearings n AMMAN LS n HE PARIET ERY PTET DI TTEFFY STIHL Inc Virginia Beach VA 2014 28 Carburetor Pressure test the carb no higher than 10 PSI and it should hold steady Open and close the butterfly and it should open smoothly Verify that the throttle shaft does not have any excessive side to side play Inspect the carb for any physical damage STIHL Inc Virginia Beach VA 2014 29 Other Observations Final Running STAL his is where any other observations about the unit not specifically covered by one of the numbered items on the STIHL Engine Check can be recorded Once repairs have been made the last part of the STIHL Engine Check document can be used as a quality control check to be sure the engine starts easily and is running to specification A Roll Out Test is done with the engine at idle speed and warmed up Hold the engine in its normal operating position Roll it over so the air filter faces up and the engine speed should not change more than 100 200 RPM Roll it over so the muffler faces up and again the engine speed should not change more than 100 200 RPM Continue this procedure by holding the engine in several different positions Any excessive change usually indicates a crankcase air leak or fuel delivery problems STIHL Inc Virginia Beach VA 2014
17. should not be blocked up with carbon deposits After removing the muffler inspect it and the exhaust gasket for damage and verify that the engine has not been running with the muffler bolts loose STIHL Inc Virginia Beach VA 2014 16 Inspect Exhaust Port and Piston With the muffler removed use a flashlight and look through the exhaust port to be sure the port Is not clogged up with carbon deposits Move the piston up and down and inspect the surface of the piston skirt for scoring or damage A piston in good condition will still have the radial machine marks across the skirt indicated little or no wear Try to observe if the rings are moving slightly when the piston is moved up and down indicating that they are free in the lands Inspect the intake side of the cylinder wall for wear or damage STIHL Inc Virginia Beach VA 2014 17 Cooling System 18 Magneto Air Gap Verify that the cooling fins are in good condition and that the air path to the flywheel and through the engine from the flywheel is not blocked or restricted in any way Line up the pole shoes in the flywheel with the magneto Observe the gap between the ighition module and the flywheel The specification is 008 It is not absolutely necessary to measure this with a gauge just be sure the flywheel is not rubbing on the module and that the gap does not look excessively wide STIHL Inc Virginia Beach VA 2014 19 Fuel
18. t to see the needle indicate that some negative pressure Is present in the tank Watch the gauge and the needle should move back up towards zero rapidly If the needle does not leak back to zero quickly the tank vent must be replaced and then re test STIHL Inc Virginia Beach VA 2014 24 Inspect Intake Side Of Piston Remove the carburetor which will require removal of the fuel hoses and undo the throttle link from the trigger Pay attention to how the linkage hooks up and routing of the hoses STIHL Inc Virginia Beach VA 2014 24 Inspect Intake Side Of Piston STAL On most two stroke engines the intake side of the piston can be inspected through the intake port but on the KM 56 RC E due to the stratified scavenge design the flange does not allow the piston to be seen On this model skip ahead to the impulse signal test and the crankcase pressure and vacuum test then come back and remove the flange and inspect the piston STIHL Inc Virginia Beach VA 2014 25 Impulse Signal Present Most two stroke engines have a passageway between the crankcase and the fuel pump side of the carburetor to cause the fuel pump diaphragm to flex back and forth with the pressure vacuum that is created by the piston moving up and down Itis rare that there is no impulse signal but always verify that it is present because no impulse signal will cause hard to diagnose unusual running behavior that will
19. the fuel line where the filter was removed and gently pump it up no higher than 10 PSI If it holds steady then the fuel hose in the tank and the carb itself passes the pressure test If it fails the molded hose in the tank must be isolated and tested separately to see if there is a leak in the hose or the carb Itis possible that the hose in the tank may have a hole or tear in it so the engine would run OK until the fuel level dropped to the point where the air in the tank would enter the hose leading to lean running even though the tank still had fuel in it STIHL Inc Virginia Beach VA 2014 22 Pressure Test Tank Be sure there is no fuel in the tank before applying any pressure to the fuel tank he pressure test verifies that the tank does not have a leak in any location such as a grommet seam cap or hose Block off one of the two hoses coming from the tank connector and pressure test through the other Apply 3 to 4 pounds of pressure and it must hold steady m If it leaks down at all use soapy water in a spray bottle to locate where the leak is STIHL Inc Virginia Beach VA 2014 23 Vacuum Test Tank Vent The tank vent on the KM 56 RC E is a one way check valve that will not let fuel leak out under pressure but will allow air into the tank as the fuel level goes down so no vacuum builds up leading to fuel starvation Heverse the tester into vacuum mode and pump hard and fas
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