FS 550
Contents
1. O o 3 aA e Use the installing tool e Fit the piston pin 1 on the e Place new cylinder gasket in 5910 890 2210 to fit hookless assembly drift 2 and slide it into position snap ring 2 in the forward the piston the pin slides home facing piston boss arrow 1 easily if the piston is heated must point left N ta ee AE Ps 398RA041 VA p 0 at 0 398RA044 VA 398RA046 VA e To ease assembly heat the e Use installing tool 1 e Lubricate the piston and piston piston slightly and slip it over the 5910 890 2210 to fit the snap rings with oil and place the piston connecting rod ring 1 on the wooden assembly block 2 1108 893 4800 e Installed position of piston 1 Arrow 2 Flywheel FS 500 550 15 e Tighten the screw until the gap a between the two ends of the hose clamp is 5 6 mm 0 20 0 24 in e Install the new piston rings in the grooves so that the radii at the ring gap face upward and meet at the fixing pin 398RA051 VA e Slide the cylinder over the piston the clamping strap is pushed downward as the piston rings slip into the cylinder Remove the clamping strap and wooden assembly block e Push the manifold onto the intake port e Use the clamping strap 1 0000 893 2600 to compres2. see 8 2 2 Pull grommet with ignition lead out of tank housing see 5 1 e Remove the cap 1 e Pull away the tank housing and push the manifold flange out of e Remove the filter 2 and fit a the intake opening at the same new one time Fuel hoses 398RA154 VA 398RA157 VA Pull off the pickup body e Take out the screws e Take out the air diverter 1 and remove the manual fuel e Pull fuel hoses out of the pump 2 and grommet 3 with grommet fuel hoses Reassemble in the reverse sequence 398RA153 VA 398RA155 VA 398RA158 VA e Pass fuel hoses through the e Remove screws from underside e Pull the cover out of it mounts grommet so that distance a is 65 1 mm 2 55 in and b is 40 1 mm 1 57 in FS 500 550 39 Reassemble in the reverse sequence Place tank housing in position e Pass throttle cable 1 and impulse hose 2 through the bo res e To fit the manifold in the tank housing intake opening wind a piece of string 1 about 15cm 6 long around the back of the manifold flange and pass the ends of the string through the intake opening e Push tank housing towards cylinder so that manifold flange locates against intake opening e Pull the ends of the string outward 40 Note The manifold flange is thus pulled through the tank housing intake opening without
3. AV System 9 1 Repair 10 Shaft 10 1 Bike Handle 10 2 Drive Shaft Flexible Liner 10 3 Drive Tube 11 Cutting Tool Drive Gearhead Disassembling Assembling Clutch Drum h h h h h b h h Noa eai n 12 Special Servicing Tools and Aids 41 41 43 43 43 44 45 45 45 48 49 12 1 Special Servicing Tools 49 12 2 Servicing Aids STIAL 1998 Andreas Stihl Waiblingen 51 1 INTRODUCTION This service manual contains detai led descriptions of all the repair and servicing procedures specific to this power tool series There are separate handbooks for servicing procedures on stand ardized parts and assemblies that are installed in several STIHL po wer tool models Reference is made to these handbooks in the appropriate chapters of this manual As the design concept of models FS 500 and FS 550 is almost identical the descriptions and servicing procedures in this manual generally apply to both mo dels Differences are described in detail You should make use of the illustrated parts lists while carrying out repair work They show the installed positions of the individual components and assemblies Refer to the latest edition of the relevant parts list to check the part numbers of any replacement parts needed Parts lists on microfiche and CD ROM are always more up to date than printed lists A fault on the power tool may have several causes Consult the troub
4. e Install the retaining ring Check running clearance rotate output shaft add or remove shim as necessary Remove screw plug from gear housing and pack gear housing with grease Note Use STIHL gear lubricant 0781 120 1117 to lubricate the bevel gear drive see 12 2 Important Pack gear housing with about 20 g 3 4 oz grease Service note When carrying out maintenance work add grease max 5 10 g 1 4 oz only if no grease can be seen on the inside of the screw plug Unscrew the tube of grease Refit the screw plug and tighten it down to 10 Nm 7 5 lbf ft Refit the grass shield if fitted Refit the deflector or stop if fitted 48 Remove the clutch housing see 9 1 e Use pliers 1 0816 610 1495 to remove the retaining ring from stub of clutch drum e Use drift 1 1108 893 4700 to press the clutch drum out of the ball bearing e Use pliers 1 0811 641 8380 to take retaining ring out of clutch housing e Remove ball bearing from clutch housing with press arbor 1 1118 893 7200 Install in the reverse sequence e Use press arbor 1 1118 893 7200 to press home ball bearing as far as stop e Press home clutch drum as far as stop with drift 1 1108 893 4700 Install the clutch housing see 9 1 FS 500 550 12 Special Servicing Tools and Aids 12 1 Special Servicing Tools 1 Locking strip for piston 2 Press sleeve 3 Installing sleev
5. 3 3 Ibf ft Install and adjust ignition module see 5 2 2 Fit the tank housing see 8 5 22 4 8 Decompression Valve Remove the shroud see 4 1 e Use standard commercial long reach 13 mm socket to unscrew the decompression valve Install new decompression valve and tighten down to 14 Nm 10 3 Ibf ft Fit the shroud 5 IGNITION SYSTEM Warning Exercise extreme caution when carrying out maintenance and repair work on the ignition system The high voltages which occur can cause serious or even fatal accidents Troubleshooting on the ignition sy stem should always begin at the spark plug See Standard Repairs Troubleshooting hand book Note The electronic breakerless ignition system basically consists of an ignition module 1 and flywheel 2 FS 500 550 5 1 Spark Plug Boot A o gt A NS DA hA ZN LESS Remove the shroud see 4 1 e Use pliers to grip the end of the Important If the spark plug ignition lead inside the spark comes with a separate terminal e Pull grommet out of the tank plug boot and pull it out nut always fit the nut on the housing thread and tighten it down securely Push grommet into the recess in the tank housing Fit the boot on the spark plug Fit the shroud see 4 1 Jameel ZS e Use pliers to grip the leg spring e Pinch hook of leg spring into the and pull it out of the spark plug center of the lead i
6. Make sure Woodruff key is properly seated Fit the flywheel Note Check position of slot Assemble all other parts in the reverse sequence Fit and tighten down flywheel nut to 30 Nm 22 Ibf ft 5 5 Short Circuit Contact Remove clutch housing see 9 1 e Take out the screw 1 e Remove top 2 of cable guide SURAN e Remove short circuit wire 1 from connector tag e Take out the screw 2 lt gt o T 5 D 8 e Pull off the guide 1 e Take out the screw 2 e Remove the short circuit contact 3 27 6 REWIND STARTER 6 1 General If the action of the starter rope becomes very stiff and the rope rewinds very slowly or not com pletely it can be assumed that the starter mechanism is in order but plugged with dirt At very low outside temperatures the lubri cating oil on the rewind spring may thicken and cause the spring windings to stick together This has a detrimental effect on the function of the starter mechanism In such a case it is sufficient to apply a few drops of paraffin kerosine to the rewind spring Then carefully pull out the starter rope several times and allow it to rewind until its normal smooth action is restored If clogged with dirt or pitch the entire starter mechanism inclu ding the rewind spring must be re moved and disassembled Take special care when removing the spring Wash all parts in paraffin or white spirit Lubricate
7. from piston e Use a piece of old piston ring to scrape the grooves clean 398RA056 VA e Install the new piston rings in the grooves so that the radii 1 face the fixing pin 2 Install the piston see 4 5 2 4 7 Crankcase 4 7 1 Crankshaft Remove the cylinder and use wooden assembly block 1108 893 4800 to hold the piston see 4 5 1 Remove the starter cup see 6 3 Remove the flywheel see 5 4 Remove the piston see 4 5 1 Take out screw 1 e Remove cable guide 2 with throttle cable 3 e Take out screws 1 e Remove the ignition module 2 17 398RA059 VA e Pull the rubber boot 1 off the e Remove upper fuel tank moun e Pull the impulse hose off the high voltage output ting screws elbow connector e Unscrew the ignition lead 2 from the contact pin and pull it out of the high voltage output Slip the rubber boot off the ignition lead 398RA062 VA e Remove lower fuel tank moun e Take out the screws ting screws Take the crankcase off the fuel tank q gt e ie is lt L D oO e Ease the grommet 1 out of the e Take out the screws e Mount the puller 1 tank housing 4119 890 4600 to the clutch side Remove the heat shield of the c
8. lt Remove the air filter see 8 1 398RA131 VA 398RA133 VA e Pull out the air diverter e Push the fuel line with nipple and clean it thoroughly onto the carburetor elbow connector Reassemble in the reverse sequence Inspect gasket in carburetor box e Pull fuel hose off carburetor s e Push the nipple into the tester s cover and replace if necessary elbow connector pressure hose Tighten down nuts to 4 5 Nm 3 3 Ibf ft wii e Fit fuel line 1 1110 141 8600 on Close the vent screw 1 on the nipple 2 0000 855 9200 rubber bulb 2 and pump air into the carburetor until the pressure gauge 3 shows a reading of approx 0 8 bar 11 5 psi 34 FS 500 550 If this pressure remains constant the carburetor is airtight However if it drops there are two possible causes 1 The inlet needle is not sealing foreign matter in valve seat or sealing cone of inlet needle is damaged or inlet control lever sticking 2 The metering diaphragm is damaged In either case the carburetor must be removed and serviced see Carburetor handbook After completing test open the vent screw and pull the fuel line off the elbow connector Push the fuel hose onto the elbow connector Install the air filter see 8 1 FS 500 550 8 2 2 Removing and Installing Troubleshooting chart see Standard Repairs Trouble shoot
9. not otherwise butt against the ball bearing e Wait for crankcase to cool down then place a new gasket on the mating face FS 500 550 398RA082 VA Use soldering iron with suitable copper attachment to heat inner race of ball bearing in starter side of crankcase to approx 150 C 300 F e Position crankcase above the crankshaft stub e Push the ball bearing squarely over the crankshaft stub Note This operation must be carried out very quickly because the crankshaft absorbs heat imme diately and will not otherwise butt against the ball bearing 398RA083 VA Insert screws and use socket 1 0812 542 2104 to tighten them down to 9 5 Nm 7 0 Ibf ft Lubricate sealing lips of oil seals with grease see 12 2 Fit installing sleeve 1 4116 893 2400 over the starter end of the crankshaft lt x gt i lt x oc a oO Slide the oil seal open side facing the crankcase over the installing sleeve e Press home with press sleeve 1 1108 893 2405 Remove the installing sleeve 21 Slide the oil seal open side facing the crankcase over the clutch end of the crankshaft e Press home with press sleeve 1 1108 893 2405 Assemble all other parts in the reverse sequence Tighten screws on heat shield to 5 0 Nm 3 7 Ibf ft Place cable guide with throttle cable in position insert screw and tighten down to 4 5 Nm
10. of 7 5 Nm 5 5 Ibf ft Reassemble all other parts in the reverse sequence Fit ignition lead in the retainers 26 5 3 Ignition Lead Remove the ignition module and take the ignition lead out of the high voltage output see 5 2 2 e Remove the spark plug boot 1 see 5 1 e Pull the grommet 2 off the ignition lead 338RA142 VA e Pull the rubber boot off the ignition lead Cut new ignition lead to length see parts list or cut to same length as old lead e Use a pointed tool awl or gimlet to pierce the center of the igni tion lead at the end which screws into the module Reassemble all other parts in the reverse sequence e Pull the ignition lead out of the crankcase FS 500 550 5 4 Flywheel 398RA104 VA Remove the clutch see 3 1 Remove segment from flywheel see 5 2 2 e Unscrew the flywheel nut 398RA105 VA e Screw the puller 1 1110 890 4500 into the flywheel e Screw home the thrust bolt until the flywheel is released lt x gt o q aa Se e Pull off the flywheel FS 500 550 Inspect the flywheel 1 and magnet poles 2 If you find any damage install a new flywheel 398RA108 VA Installing the flywheel Important Clean the stub of the crankshaft and the flywheel hub bore with a standard commercial solvent based degreasant which contains no chlorinated or halogenated hydrocarbons see 12 2 e
11. to the power head are considerably easier if it is mounted on assembly stand 2 5910 890 3100 with the aid of clamping plate 1 5910 890 2100 First remove the clutch housing and secure the powerhead to the stand with two M5x30 hex head screws 3 The complete machine or power head can then be swivelled to the best position for the ongoing repair and this leaves both hands free Always use original STIHL replacement parts They can be identified by the STIHL part number the STIHL logo and the STIHL parts symbol amp 7 The symbol may appear alone on small parts FS 500 550 2 SPECIFICATIONS 2 1 Engine STIHL single cylinder two stroke engine with special impregnated cylinder bore Displacement Bore Stroke Power output Cut off speed without cutting tool electronic speed limiter Idle speed Bearings Piston pin diameter Rewind starter Pawls Reserve pull on rope rotor Starter rope Clutch Clutch engages at Crankcase leakage test at gauge pressure under vacuum 2 2 Fuel System Carburetor Standard setting of carburetors with three adjusting screws High speed screw H Low speed screw L Carburetor leakage test at gauge pressure Function of tank vent at gauge pressure under vacuum Fuel tank capacity Octane rating Fuel mixture Mix ratio Air filter FS 500 550 FS 500 FS 550 56 5 cm 3 45 cu in 46 mm 1 81 in 34 mm 1 34 in 2 8 kW 3
12. 2 FS 500 550 e Slacken the screw Squeeze the throttle trigger as far as stop full throttle hold it there and tighten down screw to 1 0 Nm 0 75 Ibf ft Release the throttle trigger idle position The throttle lever must butt against idle speed screw s holder if fitted FS 500 550 8 FUEL SYSTEM 8 1 Air Filter Dirty and clogged air filters reduce engine power increase fuel consumption and make starting more difficult The air filter must be cleaned when there is a noticeable loss of engine power Close the choke shutter Clean away any loose dirt from around the filter and carburetor box cover 398RA127 VA e Unscrew the nuts 1 e Remove the carburetor box cover 2 lt x gt o N q oc D e e Take auxiliary filter out of carburetor box cover Dry a wet auxiliary filter then shake it clean or blow it out with compressed air If the filter is heavily loaded with dirt or damaged fit a new one e Remove the air filter Wash the filter in a fresh non flammable cleaning solution e g warm soapy water and shake dry or if possible blow out with compressed air Soften encrusted dirt by soaking the filter in cleaning solution Always replace a damaged air filter 33 8 2 Carburetor 8 2 1 Leakage Test The carburetor can be tested for leaks with the carburetor and crankcase tester 1106 850 2905 A A
13. 8 bhp at 9 400 rom 51 7 cm 3 15 cu in 44 mm 1 73 in 34 mm 1 34 in 2 4 kW 3 3 bhp at 9 400 rom 12 500 rpm 800 rpm 2 500 rpm Crankshaft supported in heavy duty ball bearings needle cages on small and big ends 10 mm 0 39 in ElastoStart Single pawl system min 1 2 turn 3 5 mm 0 14 in dia Centrifugal clutch with press fitted linings 3 250 rpm 0 5 bar 7 25 psi 0 5 bar 7 25 psi Diaphragm carburetor Open approx 1 turn Open approx 1 turn 0 8 bar 11 6 psi lt 0 3 bar 4 35 psi lt 0 05 bar 0 725 psi 0 755 1 6 US pt min 90 RON US CAN pump octane min 87 Regular brand name gasoline and two stroke engine oil 50 1 with two stroke engine oil 25 1 with other brand name two stroke air cooled engine oils Plastic filter element Auxiliary filter felt 2 3 2 4 2 5 2 5 1 2 5 2 Ignition System Gearhead Special Accessories For User For Service Type Air gap Spark plug Suppressed Electrode gap Spark plug thread Length of thread Type Gear ratio Bearings Lubrication Full harness Safety glasses Transport guard for metal cutting tools STIHL gear lubricant 80 g 3 oz tube STIHL gear lubricant 80 g 3 oz tube Carburetor parts kit Set of gaskets for FS 500 550 Electronic magneto ignition breakerless with integral trigger unit and electronic speed governor 0 2 0 3 mm 0 008 0 012 in Bosch WSR 6F NGK B
14. Control Handle 4 392RA095 VA Remove the throttle trigger see 7 1 e Lift contact spring 1 a little and remove the throttle cable 2 e Remove spring from recesses 1 and peg 2 392RA097 VA e Remove contact spring from peg 1 and collar screw 2 392RA098 VA e Take out slide control s collar screw 1 e Remove detent spring 2 x gt D D 3 lt oc A D oo e Pull slide control out of handle molding Assemble in the reverse sequence Engage contact spring correctly in groove of collar screw 31 7 3 Throttle Cable 7 3 1 Replacing 7 3 2 Adjusting All models Remove the shroud see 4 1 Remove the air filter see 8 1 Take throttle cable off the con tact spring see 7 2 398RA124 VA e Take throttle cable 1 out of Throttle lever must butt against retainer 2 and guide 3 and the idle speed screw s holder pull it out of the tank housing 4 when the throttle trigger is in the full throttle position Adjust throttle cable see 7 3 2 e Disconnect throttle cable nipple e On carburetors with an idle 1 from slotted pin 2 on throttle speed screw Throttle lever must lever butt against the idle speed screw when the trigger is in the idle position Check correct setting of idle speed screw Important Note adjustment range of idle speed screw e Take out the screw 1 e Remove top 2 of cable guide 3
15. DG P screws use for releasing only 50 FS 500 550 12 2 No Servicing Aids Part Name Lubricating grease 370 g 13 oz tube Standard commercial solvent based degreasant containing no chlorinated or halogenated hydrocarbons STIHL special lubricant Ignition lead HTR 10 m 33 Medium strength threadlocking Loctite 242 STIHL gear lubricant 80 g 3 oz tube 225 g 8 oz tube STIHL gear lubricant 80 g 3 oz tube 225 g 8 oz tube FS 500 550 Part No 0781 120 1111 0781 417 1315 0000 930 2251 0786 111 1101 0781 120 1109 0781 120 1110 0781 120 1117 0781 120 1118 Application Oil seals Cleaning crankshaft stub Bearing bore in rope rotor rewind spring in rope rotor Grub screw in gearhead annular buffers in AV housing Drive shaft in drive tube Gearhead lubrication 51
16. F and push it on as far as stop Fit retaining ring in the groove Q ar 398RA194 VA e Heat ball bearing to approx 50 C 120 F and push it on to output shaft as far as stop FS 500 550 398RA195 VA Heat gear housing to approx 180 200 C 350 390 F e Place ball bearing 1 in housing and press it home as far as stop with the press arbor 2 4116 893 7205 and installing sleeve 3 1114 893 4601 Note Installing sleeve is used only as an extension lt x gt D q oc D oO e Place preassembled output shaft in the housing FS 500 550 e Use installing sleeve 1 1119 893 2401 to press output shaft into housing as far as stop Insert grub screw in the housing and tighten it down to 4 5 Nm 3 3 Ibf ft Note If pinion shaft bearing is pro perly seated the cone of the grub screw should be visible in the neck of the gearhead 398RA198 VA e Place preassembled drive pinion 1 in the housing e Use press arbor 2 4116 893 7200 and installing sleeve 3 1114 893 4601 to press home drive pinion as far as stop Important Check that teeth of pinions engage properly during installation process Note Installing sleeve is used only as an extension Coat grub screw with Loctite see 12 2 lt x gt o N qL asi Q oO e Install the spacer washer if it was originally fitted 47 11 2 Clutch Drum
17. PMR 7 A or Champion RCJ 6Y 0 5 mm 0 020 in M14x1 25 9 5 mm 0 37 in Spiral toothed bevel gear drive 1 1 33 Deep groove ball bearings STIHL gear lubricant 0781 120 1117 0781 120 1109 0781 120 1117 4116 007 1061 4116 007 1051 FS 500 550 26 Tightening Torques DG and P screws Plastoform are used in polymer and lightmetal components These screws form a perma nent thread when they are installed for the first time They can be removed and installed as often as necessary without detrimentally affecting the strength of the screwed assembly providing the specified tightening torque is observed For this reason it is essential to use a torque wrench Fastener Thread For component Torque Remarks size Nm lbf ft Spline screw IS M4x25x10 Cover on spark plug boot shroud 2 5 1 8 Spline screw IS M4x6 Heat shield crankcase 5 0 3 7 Spline screw IS M5x28 AV housing bottom top 4 5 3 3 Plastoform screw IS P4x16 Control handle handle moldings 1 0 0 75 Collar screw IS P3 5x10 6 Detent spring slide control 1 1 0 8 Spline screw IS M5x30 Control handle 2 0 1 5 1 Plastoform screw IS P4x16 Cover guide 1 0 0 75 M10x1 Decompression valve 140 10 3 Spline screw IS M5x25 Guide crankcase 4 5 3 3 Spline screw IS M5x30 Gear housing drive tube 10 0 7 5 1 Grub screw IS M6x8 Gear housing centering screw 4 5 3 3 2 Spline screw IS M4x16 Shroud crankcase 3 5 2 6 Spline screw IS M4x20 Clamp handlebar tube 4 0 3 0 Spline screw IS M5x18 Clamp handl
18. STIHL FS 500 550 CONTENTS 1 Introduction 2 2 Specifications 3 2 1 Engine 3 2 2 Fuel System 3 2 3 Ignition System 4 2 4 Gearhead 4 2 5 Special Accessories 4 2 5 1 For User 4 2 5 2 For Service 4 2 6 Tightening Torques 5 3 Clutch 7 3 1 Removing and Disassembling 7 3 2 Assembling and Installing 8 4 Engine 9 4 1 Exhaust Muffler Spark Arresting Screen 9 4 2 Leakage Test 10 4 2 1 Preparations 10 4 2 2 Pressure Test 11 4 2 3 Vacuum Test 11 4 3 Oil Seals 12 4 4 Exposing the Cylinder 13 4 5 Cylinder and Piston 14 4 5 1 Removal 14 4 5 2 Installation 15 4 6 Piston Rings 17 4 7 Crankcase 17 4 7 1 Removing Crankshaft 17 4 7 2 Installing Crankshaft 20 4 8 Decompression Valve 22 FS 500 550 5 1 5 2 1 5 2 2 5 3 5 5 6 1 6 2 1 6 2 2 6 3 7 1 7 2 7 3 7 3 1 7 3 2 8 1 8 2 1 8 2 2 8 2 3 8 3 8 4 Ignition System 22 Spark Plug Boot 23 Ignition Module 24 Ignition Timing 24 Removing and Installing 24 Ignition Lead 26 Flywheel 27 Short Circuit Contact 27 Rewind Starter 28 General 30 Rewind Spring 28 Replacing 28 Tensioning 29 Starter Cup 30 Throttle Control 30 Throttle Trigger Interlock Lever 30 Contact Springs Detent Spring in Control Handle 31 Throttle Cable 32 Replacing 32 Adjusting 32 Fuel System 33 Air Filter 33 Carburetor 34 Leakage Test 34 Removing and Installing 35 Adjusting 36 Tank Vent 37 Pickup Body Fuel Hoses 38 Tank Housing 39 Manual Fuel Pump 40 9
19. and the faulty part replaced Note To find the leak coat the suspect area with oil and pressurize the crankcase again Bubbles will appear if a leak exists If the decompression valve is not airtight install a new one see 4 8 Repeat the pressure test Carry out the vacuum test see 4 2 3 398RA024 VA After finishing the test open the vent screw and disconnect the hose e Connect the suction hose of vacuum pump 0000 850 3501 Remove the test flange to test flange nipple Slacken off the muffler mounting screws Pull out the sealing plate and tighten down the screws to 10 Nm 7 5 lbf ft Install carburetor see 8 2 2 398RA026 VA e Close vent screw 1 on pump cylinder e Operate lever 2 until the gauge 3 indicates a vacuum of 0 5 bar 7 25 psi 11 Note If the vacuum reading remains constant or rises to no more than 0 3 bar 4 25 psi within 20 seconds it can be assumed that the oil seals are in good condition However if the pressure continues to rise reduced vacuum in the crankcase the oil seals must be replaced After finishing the test open the vent screw and disconnect the hose Remove the test flange Slacken off the muffler screws Remove the sealing plate and tighten down the screws to 10 Nm 7 5 lbf ft Install carburetor see 8 2 2 12 4 3 Oil Seals It is not necessary to disassemble the complete engine to replace
20. ating surfaces they must be cleaned very thoroughly to ensure a perfect seal Heat area of bearing seat on starter side of crankcase to approx 120 C 250 F e Fit ball bearing shoulder 1 first in crankcase by hand and push it home until it butts against the snap ring Note This operation must be carried out very quickly because the bearing absorbs heat immedi ately and begins to expand e Check that dowel pins are in e f it is not possible to heat the position If necessary drive the clutch side of the crankcase use pins into the crankcase press arbor 1 1118 893 7200 to press in the ball bearing as far Heat area of bearing seat on as stop clutch side of crankcase to approx 120 C 250 F N l Oo 0 e Fit ball bearing in crankcase by e Check that snap ring is in e f it is not possible to heat the hand and push it home as far as position in starter side of crankca starter side of the crankcase stop se or fit if necessary use press arbor 1 1118 893 7200 to press in the ball bearing as far as stop 20 FS 500 550 398RA080 VA Use soldering iron with suitable copper attachment to heat inner race of ball bearing in clutch side of crankcase to approx 150 C 300 F e Push tapered stub of crankshaft squarely into the ball bearing Note This operation must be carried out very quickly because the crankshaft absorbs heat imme diately and will
21. between the piston and crankcase 398RA033 VA Remove the cylinder gasket e Use the assembly drift 2 4116 893 4700 to push the piston pin 1 out of the piston Note If the piston pin is stuck tap the end of the drift lightly with a hammer if necessary Important Hold the piston steady during this process to ensure that no jolts are transmitted to the connecting rod Remove the piston and take the needle cage out of the connecting rod q gt o oO 3 lt x fea Q Ge e Carefully lift the cylinder up and at the same time push the manifold through the tank housing opening e Ease the hookless snap rings out of the grooves in the pistons 14 Inspect piston rings and replace if necessary see 4 6 FS 500 550 4 5 2 installation Note For instructions on how to use installing tool see Standard Repairs Troubleshooting hand book e Thoroughly clean the gasket e Push the assembly drift small seating surface 1 diameter 1 first through the piston and small end needle e Lubricate the needle cage 2 cage and line up the piston with oil and fit it in the small end
22. cover Gearhead Grass shield Cylinder crankcase Ignition module crankcase Spark plug 30 0 4 5 24 0 1 5 6 5 5 5 5 5 5 5 3 5 10 0 11 0 9 5 7 5 20 0 Place the DG or P screw in the hole and rotate it counterclockwise until it drops down slightly Tighten the screw clockwise to the specified torque This procedure ensures that the screw engages properly in the existing thread and does not form a new thread 1 with washer 2 Secure with adhesive 0786 111 1101 Loctite 242 Note Heat screws secured with adhesive with a hot air blower hair dryer before releasing max 600 rpm max 500 rom Power screwdriver speed settings for polymer Plastoform screws DG screws FS 500 550 3 CLUTCH 3 1 Removing and Disassembling Troubleshooting chart see Standard Repairs Trouble shooting handbook Remove clutch housing with drive tube see 9 1 e Take out screw 1 e Take bushes out of the clutch shoes e Swing the cover 2 open Pull off the spark plug boot Unscrew the spark plug Inspect clutch drum There e Close the decompression e Remove the washers should be no scores or signs of valve 1 excessive wear e Fit locking strip 2 Important If there are signs of 0000 893 5903 serious wear on the inside diameter fit a new clutch drum see 11 2 lt x lt x gt gt o a lt 4 qL oc oc D D z oO e Take out screws 1 e Twist the cl
23. damaging the manifold Important There must be no internal stresses in the tank housing when the seven screws are tightened down To avoid this screw home the three side screws only fingertight first Then push the crankcase and underside of the tank housing firmly together Insert the four screws in the underside and tighten them down to 5 5 Nm 4 Ibf ft Finish off by tightening down the three side screws to 5 5 Nm 4 Ibf ft 8 6 Manual Fuel Pump Remove the air filter see 8 1 e Disconnect hoses from connectors e Carefully push back the retaining tabs lt gt y amp c 8 8 e Pull fuel pump out of its seat in the tank housing Install in the reverse sequence FS 500 550 9 AV SYSTEM 9 1 Repair The anti vibration AV connection between the engine and drive tube consists of four rubber buffers annular buffers and two stop buffers in the AV housing Remove the drive tube see 10 3 Remove the bike handle 10 1 e Pry the plugs out of the annular e Take out the screws buffers Remove the two halves of the clamp e Ease locking tabs of cover strip Take out the screws e Push the annular buffers out of out of the AV housing their seats in the AV housing Remove the clutch housing Remove the cover strip e Take out the screws e Pry the annular buffers out of the Take out the screw
24. e 4 Puller 5 Jaws No 3 1 4 6 Puller 7 Crimping tool 8 Assembly drift 9 Clamping strap 10 Wooden assembly block 11 Carburetor and crankcase tester 12 Vacuum pump 13 Nipple 14 Fuel line 15 Sealing plate 16 Test flange 17 Setting gauge 18 Socket 13 mm 19 Torque wrench 20 Torque wrench 21 Spline screw socket T27x125 22 Installing tool 23 Press arbor 24 Puller 25 Circlip pliers 26 Circlip pliers C19 27 Circlip pliers A10 FS 500 550 0000 893 5903 1108 893 2405 4116 893 4601 5910 890 4400 0000 893 3706 1110 890 4500 5910 890 8210 4116 893 4700 0000 893 2600 1108 893 4800 1106 850 2905 0000 850 3501 0000 855 9200 1110 141 8600 0000 855 8106 1128 850 4200 1127 890 6400 5910 893 5608 5910 890 0301 5910 890 0302 5910 890 0311 5910 890 0312 0812 542 2104 5910 890 2210 1118 893 7200 4119 890 4600 0816 610 1495 0811 641 8380 0811 611 8200 Application Rem Blocking crankshaft Fitting oil seal Protecting oil seal starter side Removing oil seals 1 Releasing flywheel Attaching connectors to electrical wires Removing and fitting piston pin removing and installing clutch drum Compressing piston rings Fitting piston Testing carburetor for leaks Testing crankcase for leaks Sealing exhaust port for leakage test For leakage test Setting air gap between ignition module and flywheel Screws for clutch flywheel nut and unsc
25. e about boot 15 mm 9 16 from the end of the lead Unhook the leg spring from the ignition lead Pull spark plug boot off the ignition lead Coat end of the ignition lead about 20 mm 3 4 with oil Fit spark plug boot over the ignition lead lt gt lt oc oO ce e Pull the lead back into the boot so that the leg spring locates properly inside it FS 500 550 23 5 2 Ignition Module lt x gt ite a e lt 4 oc Ss ire A The ignition module accommoda tes all the components required to control ignition timing There are two electrical connecti ons on the coil body 1 the high voltage output 1 2 the connector tag 3 for the short circuit wire Accurate testing of the ignition module is only possible with sophisticated test equipment For this reason it is only necessary to carry out a spark test in the work shop A new ignition module must be installed if no ignition spark is obtained after checking that wiring and stop switch are in good condition 24 5 2 1 Ignition Timing Ignition timing is not adjustable Since there is no mechanical wear in these systems ignition timing cannot get out of adjustment How ever an internal fault in the circuit can alter the switching point in such a way that a spark test will still show the system to be in order although timing is outside the permissible tolerance This will impair engine starting a
26. ebar 4 5 3 3 Spline screw IS M5x28 Clamp AV housing 7 5 5 5 Spline screw IS M8x25 Clutch shoe flywheel 20 0 15 0 Spline screw IS M6x25 Drive tube clutch housing clamp screw 8 0 5 9 Spline screw IS M5x12 Drive tube clutch housing centering screw 4 5 3 3 Spline screw IS M5x20 clutch housing crankcase 9 5 7 0 Spline screw IS M5x20 Crankcase 9 5 7 0 Spline screw IS M5x18 Perforated rail AV housing top 4 5 3 3 Spline screw IS M5x18 Annular buffer AV housing 3 5 2 6 Spline screw IS M5x20 Muffler crankcase 10 0 7 5 Spline screw IS M5x20 Muffler cylinder 10 0 7 5 Nut M14x1 5L Cutting tool 25 0 18 5 Spline screw IS M6x50x24 Cutting tool deflector clamp drive tube 4 5 3 3 1 Spline screw IS M5x20 Screen crankcase 4 5 3 3 Self tapping screw BZ4 2x14 Screen shroud 1 5 1 1 Self tapping screw B4 2x9 5 Spark arresting screen 2 5 1 8 FS 500 550 Fastener Thread For component Torque Nm Remarks size Spline screw Nut Plastoform screw Plastoform screw Nut Spline screw Spline screw Collar screw Screw plug Spline screw Spline screw Spline screw Use the following procedure to fit a DG or P screw in an existing thread M8x1 IS M5x20 M8x1 IS P4x16 IS P6x19 M5 IS M5x20 IS M5x20 M5 M11x10 IS M6x14 IS M5x28 IS M5x20 M14x1 25 Flywheel Starter cover crankcase Starter cup Connector tag guide Backing plate tank housing Backing plate carb tank housing Support clutch housing Tank housing crankcase Carburetor box
27. excessively lean carburetor setting increases neither the engine speed nor its performance it simply increase the risk of engine damage Standard setting If the carburetor has to be adjusted from scratch first carry out the standard setting Carefully screw in both adjusting screws clockwise until they are hard against their seats Now make the following adjust ments H Open high speed screw 1 one full turn L Open low speed screw 2 one full turn FS 500 550 A slight correction to this setting may be necessary at high altitudes mountains or near sea level Use the following procedure Mount approved cutting tool Check the air filter replace if necessary Check spark arresting screen clean or replace as necessary Start the engine and allow it to warm up Turn high speed screw H clockwise for leaner mixture at high altitude or counterclockwise for richer mixture at sea level Turn screw slowly and carefully slight changes have a noticeable effect on engine running behavior Adjusting idle speed Engine stops while idling Carry out standard setting Turn the idle speed screw LA clockwise until cutting tool begins to rotate and then turn screw back one half turn FS 500 550 Cutting tool rotates while engine is idling Carry out standard setting Turn the idle speed screw LA counterclockwise until cutting tool stops rotating and then
28. il it snaps into position Fit new sintered filter in the cap Fit cap on valve body and press it down until it snaps into position Refit the fuel filler cap 38 8 4 Pickup Body Fuel Hoses The diaphragm pump draws fuel out of the tank and into the carburetor via the fuel hose Any impurities mixed with the fuel are retained by the pickup body filter The fine pores of the filter event ually become clogged with minute particles of dirt This restricts the passage of fuel and results in fuel starvation Important In the event of trouble with the fuel supply system always check the fuel tank and the pickup body first Clean the fuel tank if necessary Cleaning the fuel tank Unscrew the filler cap and drain the tank Pour a small amount of clean gasoline into the tank Close the tank and shake the unit vigorously Open the tank again and drain it Note Dispose of fuel properly Pickup body Remove the air filter see 8 1 398RA148 VA e Pull the fuel hose 1 off the elbow connector e Pull hose 2 off the manual fuel pump e Ease the grommet out of the tank housing e Remove the fuel hoses with pickup body e Pull the pickup body off the fuel hose FS 500 550 8 5 Tank Housing Drain the tank housing Remove the shroud see 4 1 Remove the carburetor take out the sleeve and washer
29. ing handbook Important In the event of trouble with the carburetor or the fuel supply system always check and clean the tank vent see 8 3 Remove the air filter see 8 1 e Disconnect manual fuel pump hose from the carburetor e Pull fuel hose off carburetor s elbow connector e Disconnect throttle cable nipple 1 from slotted pin 2 on throttle lever e Push retaining rib 1 upward Remove the fuel filler cap e Pull choke knob 2 off the shaft e Ease the grommet off the adjusting screws and take it out of the tank housing 35 398RA140 VA e Take out the screws 1 and unscrew the nuts 2 e Remove the backing plate 3 e Pull impulse hose off the elbow connector q gt y lt ce D i e Pull carburetor off the studs 36 Reassemble in the reverse sequence e Check that sleeve 1 is in manifold and washer 2 is in position Tighten down screws on backing plate to 6 5 Nm 4 8 Ibf ft and nuts to 5 5 Nm 4 Ibf ft 8 2 3 Adjusting The machines are equipped with an electronic speed limiter that operates via the ignition system Therefore the carburetor cannot be adjusted to increase the maximum engine speed beyond the preset limit Similarly the machine cannot be tuned for best performance by way of engine speed An
30. leshooting charts for all as semblies in the Standard Repairs Troubleshooting handbook Refer to the Technical Informa tion bulletins for engineering changes which have been intro duced since publication of this service manual Technical informa tion bulletins also supplement the parts list until a revised edition is issued The special servicing tools mentio ned in the descriptions are listed in the last chapter of this ma nual Use the part numbers to identify the tools in the STIHL Special Tools manual The manual lists all special servicing tools currently available from STIHL Symbols are included in the text and pictures for greater clarity The meanings are as follows In the descriptions e Action to be taken as shown in the illustration above the text Action to be taken that is not shown in the illustration above the text In the illustrations _ gt Pointer Direction of movement Service manuals and all technical information bulletins describing engineering changes are intended exclusively for the use of STIHL servicing dealers They must not be passed to third parties q ar i e lt 4 oc D oO Servicing and repairs are made considerably easier if the machine is mounted on assembly stand 2 5910 890 3100 with the aid of clamp 1 5910 890 8800 Secure the clamp to the assembly stand with two washers and two M8 nuts Servicing and repairs
31. ll twist on the tube Always leave it to dry for a while after fitting Remove the control handle see 7 1 e Take out the screw 1 e Remove bike handle 2 with clamp 8 e Take out the screws 4 e Remove the top and base of clamp 3 3 Ea K 1 __ EEKV Oe e Take out the screws 1 remove clamp moldings 2 and short tube 3 Assemble all parts in the reverse sequence Tighten down screws on bike handle clamp to 4 5 Nm 3 3 Ibf ft and screws of clamp moldings on short tube to 4 Nm 3 Ibf ft lt x gt lt A lt ac e ire a e Use jaws 1 5910 893 2700 to clamp bike handle tube in vice FS 500 550 10 2 Drive Shaft Flexible Liner The drive shaft is supported in a flexible liner inside the drive tube The ends of the drive tube are sea led with plugs Remove the gearhead see 11 1 Drive shaft lt x gt o T A lt pa e D A e Pull the drive shaft out of the drive tube Note If the shaft has turned blue fit a new one Coat the drive shaft with STIHL gear lubricant 0781 120 1109 see 12 2 before installation Important Apply the grease uniformly and thinly to the whole drive shaft Do not pump grease directly into the drive tube Push the drive shaft into the dri ve tube 43 10 3 Drive Tube 398RA181 VA e Push the drive shaft into the dri e Pull out the flexible liner e Slacken off screws o
32. n clamp ve tube until dimension A is 25 mm 1 If necessary apply slight pressure to the shaft and rotate it slowly until it can be pushed in to the specified dimension Fit the gearhead see 11 1 e Fit the flexible liner into the drive e Take the fixing screw 1 out of so that the spokes point coun the clutch housing terclockwise viewed from the ge arhead e Release the clamp screw 2 Push flexible liner about 27 mm 1 1 into the drive tube Flexible liner Insert the plug Install the drive tube see 10 3 lt gt oO q asi Q e Remove the drive tube e Pull the drive tube out of the see 10 3 clutch housing and the AV housing e Pry the plug out of the drive tube 44 FS 500 550 11 CUTTING TOOL DRIVE 11 1 Gearhead 11 1 1 Disassembling Remove the drive shaft or e Release clamp screws Remove the gearhead see 11 1 flexible liner see 10 2 Pull gearhead off the drive tube Remove the deflector or limit Install in the reverse sequence stop if fitted Degrease clamp mounting area Degrease clamp mounting area Remove the grass shield if Slide the gearhead onto the dri fitted e Push home drive tube until the ve tube and turn output shaft holes line up back and forth at the same time e Use pliers 2 0811 641 8380 so that square end of drive shaft to remove retaining ring 1 Note Drive tube is sho
33. nd running behavior 5 2 2 Removing and Installing Remove clutch housing see 9 1 Ease ignition lead grommet out of recess in tank housing see 5 1 7 398RA093 VA e Lever ignition lead out of guide in crankcase lt x gt a i lt L E o z e Remove ignition lead from the retainers FS 500 550 e Pull short circuit wire connector e Take out the screws e Pull short circuit wire off the 1 off tag ignition module e Remove short circuit wire from Pack the high voltage output with retainers 2 STIHL multipurpose grease see 12 2 Important Do not use a graphite grease Molykote or silicone insulating paste Screw ignition lead into high voltage output Slide rubber boot over the high voltage output e Ease lug of segment out of Remove the ignition module crankcase opening e Pull the rubber boot 1 off the high voltage output e Unscrew ignition lead 2 from the contact pin and pull it out of the high voltage output e Remove the segment FS 500 550 25 Place the module in position insert the screws but do not tighten them down yet Important A washer must be fit ted under each screw head e Slide the setting gauge 1 1127 890 6400 between the arms of the ignition module and the flywheel magnet poles Press the ignition module against the gauge and tighten down the mounting screws to a torque
34. r grip firmly to keep the rope tensioned Let go of the rope rotor and slowly release the starter rope so that it can rewind properly Make a loop in the starter rope e Push starter rope into notch in the rotor 398RA117 VA e Check the position of the inner e Grip the rope close to the rotor Note The rewind spring is spring loop It should be and use it to turn the rope rotor correctly tensioned when the star 2 mm 0 08 away from the star seven full turns counterclockwise ter grip sits firmly in the rope guide ter post bush without drooping to one side If this is not the case tension the Install the rope rotor see spring by one Standard Repairs Trouble additional turn shooting handbook When the starter rope is fully extended it must still be possible to rotate the rope rotor at least another half turn before maximum spring tension is reached If this is not the case pull the rope out hold the rope rotor steady and take off one turn of the rope Tension the rewind spring see 6 2 2 Do not overtension the rewind spring as this will cause it to break e Hold the rope rotor steady Fit starter cover insert screws and tighten down to 4 5 Nm e Pull out the rope with the starter 3 3 Ibf ft grip and straighten it out FS 500 550 29 6 3 Starter Cup 7 THROTTLE CONTROL 7 1 Throt
35. rankcase e Pull ignition lead 2 out of the housing 18 FS 500 550 398RA073 VA e Turn thrust bolt clockwise When fitting a replacement e Use press arbor 1 until the crankshaft is released crankshaft always install new oil 1118 893 7200 to remove ball from the ball bearing The two seals and ball bearings bearing halves of the crankcase separate in this process e Carefully knock the oil seal out of Inspect both halves of the crank the clutch side of the crankcase case for cracks and replace if Remove the crankcase gasket necessary Note The complete crankcase must be replaced even if only one half is damaged If necessary take the snap ring out of the crankcase e Press the crankshaft out of the e Use press arbor 1 starter side of the crankcase 1118 893 7200 to remove ball bearing e The crankshaft 1 connecting e Pry the oil seal out of the starter rod 2 and needle bearing form side of the crankcase an inseparable unit It must always be replaced as a complete unit FS 500 550 19 4 7 2 Installing Crankshaft New crankcases come with Note This operation must be factory installed ball bearings carried out very quickly because the bearing absorbs heat immedi Stamp the machine number onthe ately and begins to expand new crankcase with 2 5 mm 0 1 figure stamps If the original crankcase is used again remove the gasket residue and clean the m
36. rewing starter cup 0 5 18 Nm 5 0 4 13 5 Ibf ft 3 6 80 Nm 5 4 4 60 Ibf ft 3 IS screws Installing hookless snap rings in piston Removing and installing ball bearings Removing crankshaft External circlip on clutch housing Internal circlip in clutch housing and gearhead External circlip on drive pinion 49 28 T handle screwdriver QI T27x150 5910 890 2400 For all IS screws 4 29 Screwdriver T20x100 5910 890 2301 Separating handle moldings 30 Assembly drift 1108 893 4700 Removing and installing clutch drum pressing drive pinion out of ball bearing 31 Press arbor 4116 893 7205 Installing ball bearing in gear housing 32 Installing sleeve 1114 893 4601 33 Press arbor 4116 893 7200 Installing preassembled drive pinion in gear housing 34 Press sleeve 1119 893 2401 Installing preassembled output shaft in gear housing 35 Press arbor 1118 893 7200 Removing and installing ball bearing in clutch housing 36 Vice jaws 5910 893 2700 Holding drive tube and bike handle 37 Assembly stand 5910 890 3100 Holding FS units 38 Clamp 5910 890 8800 Holds drive tube of FS units for repairs in conjunction with assembly stand 39 Clamping plate 5910 890 2100 Holds powerhead of FS units for repairs in conjunction with assembly stand Remarks 1 Equivalent to puller 0000 890 4400 but with longer spindle 5910 890 8400 Always use torque wrench to tighten DG P screws 2 3 Wrench has optical acoustic signal 4 On
37. s clutch housing Note Fourth screw not visible in Separate the two halves of the this view AV housing Remove the clutch housing FS 500 550 41 Reassemble in the reverse sequence e Take the stop buffers out of the housing moldings e Insert annular buffer small diameter first from the clutch side until its groove 1 engages the housing rib 2 Tighten down AV housing screws to 4 5 Nm 3 3 Ibf ft Tighten down screws on perforated rail to 4 5 Nm 3 3 Ibf ft Tighten down screws in annular buffers in the clutch housing to 3 5 Nm 2 6 Ibf ft e To replace the upper half of the housing take out the screws 1 e Remove the perforated rail 2 lt x gt ite N q D 0 e To replace the nut 1 remove e Plugs 2 have to be fitted in the shakeproof washer 2 with the annular buffers 1 in the AV hou nut sing press them home as far as center 42 e Install annular buffers so that the housing rib 1 locates in the center groove 2 Do not tighten the screws in the two halves of the clamp until the drive tube has been fitted see 10 3 Tighten down clutch housing screws to 9 5 Nm 7 lbf ft FS 500 550 10 SHAFT 10 1 Bike Handle To replace left grip carefully cut it open and pull it off Coat inside of new grip with a little lubricant e g washing up liquid Note If too much lubricant is used the grip wi
38. s the piston rings around the piston e Note installed position of manifold Check that the piston rings are correctly positioned Lubricate the inside of the cylinder with oil and line it up so that it is positioned as it will be in the installed condition It is important to observe this point as the piston rings might other wise break e Push the hose clamp over the manifold The screw must be horizontal and the screw head must point to the right 16 e To fit the manifold in the tank housing intake opening wind a piece of string 1 about 15cm 6 long around the back of the manifold flange and pass the ends of the string through the intake opening e Push cylinder towards tank housing so that manifold flange locates against intake opening FS 500 550 e Pull the ends of the string outward Note The manifold flange is thus pulled through the tank housing intake opening without damaging the manifold 398RA054 VA Carefully line up the cylinder and gasket e Use socket 1 0812 542 2104 to tighten down cylinder base screws to 9 5 Nm 7 lbf ft Assembly is now a reversal of the disassembly sequence FS 500 550 4 6 Piston Rings Remove the piston see 4 5 1 Note The piston must be removed to make sure that no residue can fall into the crankcase when installing the piston rings and cleaning their grooves Remove rings
39. seat Remove the installing sleeve e Apply the puller 1 5910 890 4400 with No 3 1 Fit the starter cup see 6 3 jaws 0000 893 3706 Tension the arms Pull out the oil seal Important Take care not to damage crankshaft stub Clean sealing surface with a standard solvent based de greasant containing no chlorina Take the sleeve 1 out of the ted or halogenated hydrocarbons manifold see 12 2 e Take the washer 2 off the studs Lubricate sealing lips of oil seal with grease see 12 2 e Slip installing sleeve 1 4116 893 4601 over the end of the crankshaft FS 500 550 13 Cylinder and Piston Removal 45 4 5 1 Preparations see 4 4 Remove the spark plug Unscrew the decompression valve Pull the cylinder off the piston e Release the hose clamp 1 e Pull the manifold 2 off the intake port Inspect the cylinder and replace it if necessary If anew cylinder has to be instal led always fit the matching piston New cylinders are only supplied complete with piston for this reason o D T e Le O lume e Unscrew the four cylinder base screws through the holes in the cylinder Before removing the piston decide whether or not the cranks haft has to be removed as well To remove the nuts for the star ter cup and flywheel block the crankshaft by sliding the wooden assembly block
40. sting screen if necessary Tighten down screws to 2 5 Nm 1 8 lbf ft Tighten down shroud screws to 3 5 Nm 2 6 lbf ft and lower screws on guard screen to 4 5 Nm 3 3 Ibf ft Take out screw 1 e Swing the cover 2 open Pull off the spark plug boot FS 500 550 398RA016 VA oy YS OS S S S S S oo D Muffler Remove the shroud e Take out the screws Lift away the muffler e Remove the gasket Reassemble in the reverse sequence Use a new gasket Tighten down screws to 10 Nm 7 5 lbf ft 4 2 Leakage Test Defective oil seals gaskets cracks in castings or a faulty sea ling ring between the carburetor housing and cylinder are the usu al causes of leaks Such faults allow air to enter the engine and thus upset the fuel air mixture This makes adjustment of the prescribed idle speed difficult if not impossible Moreover the transition from idle speed to part or full throttle is not smooth The crankcase can be checked thoroughly for leaks with the carburetor and crankcase tester and the vacuum pump 10 4 2 1 Preparations Back off the muffler mounting screws half way see 4 1 e Slide the sealing plate 1 0000 855 8106 between the gasket and cylinder exhaust port and retighten the mounting screws moderately Note The sealing plate must completel
41. the oil seals Clutch side Remove the flywheel see 5 4 e Remove key from crankshaft Tap the oil seal with a suitable piece of pipe or a punch to release it from its seat S S S S g a SD e Apply the puller 1 5910 890 4400 with No 3 1 jaws 0000 893 3706 398RA028 VA Tension the arms Pull out the oil seal Important Take care not to damage crankshaft stub Clean sealing surface with a standard solvent based degrea sant containing no chlorinated or halogenated hydrocarbons see 12 2 Lubricate sealing lips of oil seal with grease see 12 2 Slip the oil seal open side facing the crankcase over the crankshaft stub 398RA029 VA e Press home with press sleeve 1 1108 893 2405 Fit the key in the crankshaft Install the flywheel see 5 4 FS 500 550 44 Exposing the Cylinder Always check and if necessary repair the fuel system carburetor air filter and ignition system before looking for faults on the engine Troubleshooting chart see Standard Repairs Trouble shooting handbook Remove the muffler see 4 1 Remove the carburetor Starter side Push the oil seal open side see 8 2 2 facing the crankcase over the Remove the starter cup see 6 3 installing sleeve Tap the oil seal with a suitable e Press home with press sleeve piece of pipe or a punch to 1 1108 893 2405 release it from its
42. the rewind spring and starter post with STIHL special lubricant see 12 2 before installing 28 Rewind Spring Replacing Troubleshooting chart see Standard Repairs Trouble shoo ting handbook e Take out the screws e Remove the starter cover Remove the rope rotor see Standard Repairs Trouble shoo ting handbook Take out the screw and remove any remaining pieces of spring from the starter cover Note The replacement spring co mes ready for installation with spring housing It should be lubricated with a few drops of STIHL special lubricant before installation see 12 2 398RA112 VA mC e Place the rewind with spring hou sing bottom facing up in the starter cover Engage the outer spring loop as shown in the illu stration see arrow Caution The rewind spring may pop out and uncoil during installation If the rewind spring has popped out refit it as follows e Position the outer spring loop about 20 mm 3 4 from the edge of the spring housing distance a e Refit rewind spring in fan hou sing in the clockwise direction starting outside and working inwards FS 500 550 6 2 2 Tensioning e Place the wooden assembly block 1 1108 893 4800 across the spring housing to simplify refitting Hold the starte
43. tle Trigger Interlock Lever a gt f 3 is lt oc A D oO Remove the starter cover see 6 2 1 Block piston with locking strip see 3 1 e Unscrew the nut 1 e Pull off the starter cup 2 Reassemble in the reverse sequence Tighten down nut to 24 Nm 17 7 lbf ft 30 e Take out screw and washer e Remove the torsion spring Pull off the control handle 392RA084 VA 392RA08 Warning To avoid risk of electric e Take the throttle trigger 1 with shock do not start the unit while torsion spring 2 and throttle the control handle is open cable 3 off the peg e Remove screws with screwdriver 1 5910 890 2301 Separate the control handle lt lt 3 B S Q lt iia oc A g D oO e Lift the interlock lever 1 slightly e Disconnect throttle cable from and turn it to one side until the trigger torsion spring 2 is relaxed Assemble in the reverse sequence e Pull the interlock lever off the peg FS 500 550 392RA089 VA e Attach the throttle cable then position torsion spring as shown and push its long arm into the slot 392RA090 VA e The interlock lever must be behind the throttle trigger 392RA096 VA e Check correct positions of throttle cable 1 contact spring 2 protective tube 3 and insulator 4 FS 500 550 7 2 Contact Springs Detent Spring in
44. turn it about another half turn in the same direction 8 3 Tank Vent Correct operation of the carburetor is only possible if atmospheric pressure and internal fuel tank pressure are equal at all times This is ensured by the tank vent Important If problems occur on the carburetor or the fuel supply system always check and clean the tank vent Check function by performing pressure and vacuum tests on the tank via the fuel hose Equalization of pressure Equalization of pressure from the outside inwards takes place via the hole in the fuel filler cap the sintered filter the valve and holes in the cap 398RA146 VA Equalization of pressure from the inside outwards takes place via the holes in the cap the hole in the valve body the sintered filter and the hole in the fuel filler cap 37 Cleaning Unscrew the fuel filler cap e Ease the cap 1 off the valve body 2 e Take sintered filter 3 out of cap e Pry valve body out of fuel filler cap 4 e Pry sintered filter 5 out of fuel filler cap Wash valve body in clean gasoline e If diaphragm in the valve 6 is damaged pull it out of valve body and fit new one e Push new sintered filter 5 into filler cap e Fit sealing ring 7 over valve body Fit valve body in filler cap and press it home unt
45. utch shoes and detach the spring e Remove clutch shoes 2 with washers and bushes Important Clutch shoes must always be replaced in pairs FS 500 550 7 3 2 Assembling and Installing Pull locking strip out of cylinder Fit spark plug and tighten down to 20 Nm 15 lbf ft Important If the spark plug comes with a separate terminal nut always fit the nut on the thread and tighten it down securely Fit the boot on the spark plug e Attach spring to clutch shoes e Insert bushes in the clutch shoes Close the cover and tighten screw to 2 5 Nm 1 8 lbf ft Fit clutch housing with drive tube see 9 1 TK v G OL 398RA008 VA Q gt e Fit the washers e Fit screws with washers J S 4 vi NG e Fit clutch shoes with spring so e Tighten down screws to 20 Nm that the arrows point coun 15 lbf ft terclockwise 8 FS 500 550 4 ENGINE 4 1 Exhaust Muffler Spark Arresting Screen Troubleshooting chart see Standard Repairs Trouble shooting handbook e Remove upper screws 1 from shroud 2 e Lift away shroud with guard screen UYVYVYYVYUYVUYVYYUUU ANNANAAAAAAA 398RA015 VA Spark arresting screen e Take out screws 1 e Remove lower screws from guard screen e Remove baffle 2 e Remove spark arresting screen 3 Clean or replace spark arre
46. wn engages the square socket in dri next to AV housing to illustrate ve pinion e Remove the spacer washer 3 position of hole Push the gearhead as far as Push home the drive tube and stop and line it up turn gearhead output shaft back and forth at the same time so Tighten down clamp screws to that square end of drive shaft 10 Nm 7 5 lbf ft engages the square socket in drive pinion Tighten down centering screw to 4 5 Nm 3 3 Ibf ft and clamp screw to 8 0 Nm 5 9 lbf ft Tighten down screws on clamp to 7 5 Nm 5 5 Ibf ft lt x gt re q fso D ce e Take out the grub screw FS 500 550 45 Heat gear housing to approx 180 200 C 350 390 F and remove parts from input end of gearhead first and then the output end by knocking it against a wooden base lt x gt nu D lt L oc D oO e Use drift 1 1108 893 4700 to drive pinion out of ball bearing Remove spacer washer if fitted from the drive pinion Clean all parts and check their serviceability Note Drive shaft with bevel gear and drive pinion can only be replaced as a complete assembly set of pinions e Press the output shaft out of the ball bearing e Use pliers 1 0811 611 8200 to remove retaining ring from drive pinion 46 11 1 2 Assembling e Slip spacer washer 1 if it was Originally fitted over the drive pinion 2 e Heat ball bearing 3 to approx 50 C 120
47. y fill the space between the two mounting screws Remove the carburetor see 8 2 2 Set the piston to top dead center T D C This can be checked through the inlet port Make sure the spark plug is properly tightened down Close the decompression valve e Check that sleeve 1 is in manifold and washer 2 is in position e Locate the test flange 1 1128 850 4200 on the studs and push the pin 2 into the impulse hose 3 at the same time Push the test flange fully home e Fit and tighten down the nuts firmly FS 500 550 4 2 2 Pressure Test 398RA024 VA Carry out preparations see 4 2 1 e Connect pressure hose of tester 1106 850 2905 to nipple on test flange 143RA046 VA e Close the vent screw 1 on the rubber bulb Use rubber bulb to pump air into the crankcase until the gauge indicates a pressure of 0 5 bar 7 25 psi If this pressure remains constant for at least 20 seconds the crankcase and decompression valve are airtight FS 500 550 4 2 3 Vacuum Test Oil seals tend to fail when sub jected to a vacuum i e the sealing lip lifts away from the crankshaft during the piston s induction stroke because there is no internal counterpressure An additional test can be carried out with the vacuum pump to detect this kind of fault Carry out preparations e However if the indicated see 4 2 1 pressure drops the leak must be located
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