STIHL FS 500, 550 CONTENTS 2 5. Ignition System 22 9. AV...

1. Introduction 2

2. Specifications 3

2.1 Engine 32.2 Fuel System 32.3 Ignition System 42.4 Gearhead 42.5 Special Accessories 42.5.1 For User 42.5.2 For Service 42.6 Tightening Torques 5

3. Clutch 7

3.1 Removing andDisassembling 7

3.2 Assembling andInstalling 8

4. Engine 9

4.1 Exhaust Muffler/Spark Arresting Screen 9

4.2 Leakage Test 104.2.1 Preparations 104.2.2 Pressure Test 114.2.3 Vacuum Test 114.3 Oil Seals 124.4 Exposing the Cylinder 134.5 Cylinder and Piston 144.5.1 Removal 144.5.2 Installation 154.6 Piston Rings 174.7 Crankcase 174.7.1 Removing Crankshaft 174.7.2 Installing Crankshaft 204.8 Decompression Valve 22

5. Ignition System 22

5.1 Spark Plug Boot 235.2 Ignition Module 245.2.1 Ignition Timing 245.2.2 Removing and

Installing 245.3 Ignition Lead 265.4 Flywheel 275.5 Short Circuit Contact 27

6. Rewind Starter 28

6.1 General 306.2 Rewind Spring 286.2.1 Replacing 286.2.2 Tensioning 296.3 Starter Cup 30

7. Throttle Control 30

7.1 Throttle Trigger/Interlock Lever 30

7.2 Contact Springs/DetentSpring in ControlHandle 31

7.3 Throttle Cable 327.3.1 Replacing 327.3.2 Adjusting 32

8. Fuel System 33

8.1 Air Filter 338.2 Carburetor 348.2.1 Leakage Test 348.2.2 Removing and

Installing 358.2.3 Adjusting 368.3 Tank Vent 378.4 Pickup Body/Fuel

Hoses 388.5 Tank Housing 398.6 Manual Fuel Pump 40

9. AV System 41

9.1 Repair 41

10. Shaft 43

10.1 Bike Handle 4310.2 Drive Shaft/

Flexible Liner 4310.3 Drive Tube 44

11. Cutting ToolDrive 45

11.1 Gearhead 4511.1.1 Disassembling 4511.1.2 Assembling 4611.2 Clutch Drum 48

12. Special ServicingTools and Aids 49

12.1 Special Servicing Tools 4912.2 Servicing Aids 51

pqfeF

© 1998, Andreas Stihl, Waiblingen

STIHL FS 500, 550CONTENTS

FS 500, 550 1

This service manual contains detai-led descriptions of all the repairand servicing procedures specificto this power tool series.There are separate handbooks forservicing procedures on stand-ardized parts and assemblies thatare installed in several STIHL po-wer tool models. Reference ismade to these handbooks in theappropriate chapters of thismanual.

As the design concept of modelsFS 500 and FS 550 is almostidentical, the descriptions andservicing procedures in thismanual generally apply to both mo-dels. Differences are described indetail.

You should make use of theillustrated parts lists while carryingout repair work. They show theinstalled positions of the individualcomponents and assemblies.

Refer to the latest edition of therelevant parts list to check the partnumbers of any replacement partsneeded.Parts lists on microfiche and CD-ROM are always more up to datethan printed lists.

A fault on the power tool may haveseveral causes. Consult thetroubleshooting charts for all as-semblies in the "Standard Repairs,Troubleshooting" handbook.

Refer to the "Technical Informa-tion" bulletins for engineeringchanges which have been intro-duced since publication of thisservice manual. Technical informa-tion bulletins also supplement theparts list until a revised edition isissued.

The special servicing tools mentio-ned in the descriptions arelisted in the last chapter of this ma-nual.Use the part numbers to identifythe tools in the "STIHL SpecialTools" manual.The manual lists all specialservicing tools currently availablefrom STIHL.

Symbols are included in the textand pictures for greater clarity.The meanings are as follows:

In the descriptions:

• = Action to be taken asshown in the illustration(above the text)

- = Action to be taken thatis not shown in theillustration(above the text)

In the illustrations:

= Pointer

= Direction of movement

Service manuals and all technicalinformation bulletins describingengineering changes are intendedexclusively for the use of STIHLservicing dealers. They must notbe passed to third parties.

Servicing and repairs are madeconsiderably easier if the machineis mounted on assembly stand (2)5910 890 3100 with the aid ofclamp (1) 5910 890 8800.

Secure the clamp to the assemblystand with two washers and twoM8 nuts.

Servicing and repairs to the power-head are considerably easier if it ismounted on assembly stand (2)5910 890 3100 with the aid ofclamping plate (1) 5910 890 2100.

First remove the clutch housingand secure the powerhead to thestand with two M5x30 hex. headscrews (3).

The complete machine or power-head can then be swivelled to thebest position for the ongoing repairand this leaves both hands free.

Always use original STIHLreplacement parts.They can be identified by theSTIHL part number,thepqfeF logoand the STIHL parts symbolEThe symbol may appear alone onsmall parts.

1. INTRODUCTION

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2 FS 500, 550

2.1 Engine

STIHL single cylinder two-stroke engine with special impregnated cylinder bore

FS 500 FS 550

Displacement: 51.7 cm3 (3.15 cu.in) 56.5 cm3 (3.45 cu.in)Bore: 44 mm (1.73 in) 46 mm (1.81 in)Stroke: 34 mm (1.34 in) 34 mm (1.34 in)Power output: 2.4 kW (3.3 bhp) 2.8 kW (3.8 bhp)

at 9,400 rpm at 9,400 rpmCut-off speed withoutcutting tool(electronic speed limiter): 12,500 rpm (+ 800 rpm)Idle speed: 2,500 rpmBearings: Crankshaft supported in heavy-duty ball bearings,

needle cages on small and big endsPiston pin diameter: 10 mm (0.39 in)Rewind starter: ElastoStartPawls: Single pawl systemReserve pull on rope rotor: min. 1/2 turnStarter rope: 3.5 mm (0.14 in) dia.Clutch: Centrifugal clutch with press-fitted liningsClutch engages at: 3,250 rpmCrankcase leakagetestat gauge pressure: 0.5 bar (7.25 psi)under vacuum: 0.5 bar (7.25 psi)

2.2 Fuel System

Carburetor: Diaphragm carburetorStandard setting of carburetorswith three adjusting screwsHigh speed screw H: Open approx. 1 turnLow speed screw L: Open approx. 1 turnCarburetor leakage testat gauge pressure: 0.8 bar (11.6 psi)Function of tank ventat gauge pressure: ≤ 0.3 bar (4.35 psi)under vacuum: ≤ 0.05 bar (0.725 psi)Fuel tank capacity: 0.755 l (1.6 US pt)Octane rating: min. 90 RON (US/CAN; pump octane min. 87)Fuel mixture: Regular brand name gasoline

and two-stroke engine oilMix ratio: 50:1 with two-stroke engine oil

25:1 with other brand name two-stroke, air-cooled engine oilsAir filter: Plastic filter element

Auxiliary filter (felt)

2. SPECIFICATIONS

FS 500, 550 3

2.3 Ignition System Type: Electronic magnetoignition (breakerless)with integral trigger unitand electronic speedgovernor

Air gap: 0.2 - 0.3 mm (0.008 - 0.012 in)Spark plug (suppressed): Bosch WSR 6F,

NGK BPMR 7 A orChampion RCJ 6Y

Electrode gap: 0.5 mm (0.020 in)Spark plug thread: M14x1.25Length of thread: 9.5 mm (0.37 in)

2.4 Gearhead Type: Spiral-toothedbevel gear drive

Gear ratio: 1:1.33

Bearings: Deep groove ball bearings

Lubrication: STIHL gear lubricant 0781 120 1117

2.5 Special Accessories

2.5.1 For User Full harnessSafety glassesTransport guard formetal cutting toolsSTIHL gear lubricant (80 g/3 oz tube) 0781 120 1109STIHL gear lubricant (80 g/3 oz tube) 0781 120 1117

2.5.2 For Service Carburetor parts kit 4116 007 1061Set of gaskets for FS 500, 550 4116 007 1051

4 FS 500, 550

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 necessarywithout detrimentally affecting the strength of the screwed assembly, providing the specified tightening torque isobserved. For this reason it is essential to use a torque wrench.

Fastener Thread For component Torque Remarkssize Nm lbf.ft

Spline screw IS-M4x25x10 Cover on spark plug boot/shroud 2.5 1.8Spline screw IS-M4x6 Heat shield/crankcase 5.0 3.7Spline screw IS-M5x28 AV housing, bottom/top 4.5 3.3Plastoform screw IS-P4x16 Control handle/handle moldings 1.0 0.75Collar screw IS-P3.5x10.6 Detent spring/slide control 1.1 0.8Spline screw IS-M5x30 Control handle 2.0 1.5 1)Plastoform screw IS-P4x16 Cover/guide 1.0 0.75

M10x1 Decompression valve 14.0 10.3Spline screw IS-M5x25 Guide/crankcase 4.5 3.3Spline 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 2.6Spline screw IS-M4x20 Clamp/handlebar/tube 4.0 3.0Spline screw IS-M5x18 Clamp/handlebar 4.5 3.3Spline screw IS-M5x28 Clamp/AV housing 7.5 5.5Spline screw IS-M8x25 Clutch shoe/flywheel 20.0 15.0Spline screw IS-M6x25 Drive tube/clutch housing

(clamp screw) 8.0 5.9Spline screw IS-M5x12 Drive tube/clutch housing

(centering screw) 4.5 3.3Spline screw IS-M5x20 clutch housing/crankcase 9.5 7.0Spline screw IS-M5x20 Crankcase 9.5 7.0Spline screw IS-M5x18 Perforated rail/AV housing, top 4.5 3.3Spline screw IS-M5x18 Annular buffer/AV housing 3.5 2.6Spline screw IS-M5x20 Muffler/crankcase 10.0 7.5Spline screw IS-M5x20 Muffler/cylinder 10.0 7.5Nut M14x1.5 L Cutting tool 25.0 18.5Spline screw IS-M6x50x24 Cutting tool deflector/clamp/

drive tube 4.5 3.3 1)Spline screw IS-M5x20 Screen/crankcase 4.5 3.3Self-tapping screw BZ4.2x14 Screen/shroud 1.5 1.1Self-tapping screw B4.2x9.5 Spark arresting screen 2.5 1.8

2.6 Tightening Torques

FS 500, 550 5

Fastener Thread For component Torque Remarkssize Nm lbf.ft

M8x1 Flywheel 30.0 22.0Spline screw IS-M5x20 Starter cover/crankcase 4.5 3.3Nut M8x1 Starter cup 24.0 17.7Plastoform screw IS-P4x16 Connector tag/guide 1.5 1.1Plastoform screw IS-P6x19 Backing plate/tank housing 6.5 4.8Nut M5 Backing plate/carb/tank housing 5.5 4.0Spline screw IS-M5x20 Support/clutch housing 5.5 4.0Spline screw IS-M5x20 Tank housing/crankcase 5.5 4.0Collar screw M5 Carburetor box cover 3.5 2.6Screw plug M11x10 Gearhead 10.0 7.5Spline screw IS-M6x14 Grass shield 11.0 8.1Spline screw IS-M5x28 Cylinder/crankcase 9.5 7.0Spline screw IS-M5x20 Ignition module/crankcase 7.5 5.5 1)

M14x1.25 Spark plug 20.0 15.0

Use the following procedure to fit a DG or P screw in an existing thread:

– 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 washer2) Secure with adhesive 0786 111 1101 (Loctite 242).

Note: Heat screws secured with adhesive with a hot air blower (hair dryer) before releasing.Power screwdriver speed settings for polymer: Plastoform screws max. 600 rpm

DG screws max. 500 rpm

6 FS 500, 550

Troubleshooting chart - see"Standard Repairs, Trouble-shooting" handbook.

- Remove clutch housing withdrive tube - see 9.1.

• Inspect clutch drum. Thereshould be no scores or signs ofexcessive wear.

Important : If there are signs ofserious wear on the insidediameter, fit a new clutch drum -see 11.2.

• Take out screw (1).

• Swing the cover (2) open.

- Pull off the spark plug boot.

- Unscrew the spark plug.

• Close the decompressionvalve (1).

• Fit locking strip (2)0000 893 5903.

• Take out screws (1).

• Remove clutch shoes (2) withwashers and bushes.

• Take bushes out of the clutchshoes.

• Remove the washers.

• Twist the clutch shoes anddetach the spring.

Important : Clutch shoes mustalways be replaced in pairs.

3. CLUTCH3.1 Removin g and Disassembling

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• Attach spring to clutch shoes.

• Fit the washers.

• Fit clutch shoes with spring sothat the arrows point coun-terclockwise.

• Insert bushes in the clutch shoes.

• Fit screws with washers.

• Tighten down screws to 20 Nm(15 lbf.ft).

- Pull locking strip out of cylinder.

- Fit spark plug and tighten downto 20 Nm (15 lbf.ft).

Important : If the spark plugcomes with a separate terminalnut, always fit the nut on thethread and tighten it downsecurely.

- Fit the boot on the spark plug.

- Close the cover and tightenscrew to 2.5 Nm (1.8 lbf.ft).

- Fit clutch housing with drive tube- see 9.1.

3.2 Assembling and Installing

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Spark arresting screen

• Remove lower screws fromguard screen.


• Swing the cover (2) open.

- Pull off the spark plug boot.

• Remove upper screws (1) fromshroud (2).

• Lift away shroud with guardscreen.


• Remove baffle (2).

• Remove spark arrestingscreen (3).

- Clean or replace spark arrestingscreen if necessary.

- Tighten down screws to 2.5 Nm(1.8 lbf.ft).

- Tighten down shroud screws to3.5 Nm (2.6 lbf.ft) and lowerscrews on guard screen to4.5 Nm (3.3 lbf.ft).

Muffler

- Remove the shroud.

• Take out the screws.

- Lift away the muffler.

• Remove the gasket.

Reassemble in the reversesequence.

- Use a new gasket.

- Tighten down screws to 10 Nm(7.5 lbf.ft).

4. ENGINE4.1 Exhaust Muffler/Spark Arresting Screen

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Defective oil seals, gaskets,cracks in castings or a faulty sea-ling ring between the carburetorhousing and cylinder are the usu-al causes of leaks. Such faultsallow air to enter the engine andthus upset the fuel-air mixture.

This makes adjustment of theprescribed idle speed difficult, ifnot impossible.

Moreover, the transition from idlespeed to part or full throttle is notsmooth.

The crankcase can be checkedthoroughly for leaks with thecarburetor and crankcase testerand the vacuum pump.

- Back off the muffler mountingscrews half-way - see 4.1.

• Slide the sealing plate (1)0000 855 8106 between thegasket and cylinder exhaustport and retighten the mountingscrews moderately.

Note: The sealing plate mustcompletely fill the space betweenthe two mounting screws.

- Remove the carburetor -see 8.2.2.

- Set the piston to top dead center(T.D.C.). This can be checkedthrough the inlet port.

- Make sure the spark plug isproperly tightened down.

- Close the decompression valve.

• Check that sleeve (1) is inmanifold and washer (2) is inposition.

• Locate the test flange (1) 1128850 4200 on the studs and pushthe pin (2) into the impulse hose(3) at the same time.

- Push the test flange fully home.

• Fit and tighten down the nutsfirmly.

4.2 Leakage Test 4.2.1 Preparations

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- Carry out preparations -see 4.2.1.

• Connect pressure hose of tester1106 850 2905 to nipple on testflange.

• Close the vent screw (1) onthe rubber bulb.

- Use rubber bulb to pump air intothe crankcase until the gaugeindicates a pressure of 0.5 bar(7.25 psi). If this pressureremains constant for at least20 seconds, the crankcase anddecompression valve are airtight.

• However, if the indicatedpressure drops, the leakmust be located and thefaulty part replaced.

Note: To find the leak, coat thesuspect area with oil andpressurize the crankcase again.Bubbles will appear if a leak exists.

- If the decompression valve is notairtight, install a new one -see 4.8.

- Repeat the pressure test.

- Carry out the vacuum test -see 4.2.3.

- After finishing the test, open thevent screw and disconnect thehose.

- Remove the test flange.

- Slacken off the muffler mountingscrews.

- Pull out the sealing plate andtighten down the screws to10 Nm (7.5 lbf.ft).

- Install carburetor - see 8.2.2.

Oil seals tend to fail when sub-jected to a vacuum, i.e. the sealinglip lifts away from the crankshaftduring the piston’s induction strokebecause there is no internalcounterpressure.

An additional test can be carriedout with the vacuum pump todetect this kind of fault.

- Carry out preparations -see 4.2.1.

• Connect the suction hose ofvacuum pump 0000 850 3501to test flange nipple.

• Close vent screw (1) on pumpcylinder.

• Operate lever (2) until the gauge(3) indicates a vacuum of 0.5 bar(7.25 psi).

4.2.2 Pressure Test 4.2.3 Vacuu m Test

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Note: If the vacuum readingremains constant, or rises to nomore than 0.3 bar (4.25 psi) within20 seconds, it can be assumedthat the oil seals are in goodcondition.However, if the pressure continuesto rise (reduced vacuum in thecrankcase), the oil seals must bereplaced.

- After finishing the test, open thevent screw and disconnect thehose.

- Remove the test flange.

- Slacken off the muffler screws.

- Remove the sealing plate andtighten down the screws to 10Nm (7.5 lbf.ft).

- Install carburetor - see 8.2.2.

It is not necessary to disassemblethe complete engine to replace theoil seals.

Clutch side:

- Remove the flywheel - see 5.4.

• Remove key from crankshaft.

- Tap the oil seal with a suitablepiece of pipe or a punch torelease it from its seat.

• Apply the puller (1)5910 890 4400 (with No. 3.1jaws 0000 893 3706).

- Tension the arms.

- Pull out the oil seal.

Important : Take care not todamage crankshaft stub.

- Clean sealing surface with astandard solvent-based degrea-sant containing no chlorinated orhalogenated hydrocarbons -see 12.2.

- Lubricate sealing lips of oil sealwith grease - see 12.2.

- Slip the oil seal, open sidefacing the crankcase, over thecrankshaft stub.

• Press home with press sleeve(1) 1108 893 2405.

- Fit the key in the crankshaft.

- Install the flywheel - see 5.4.

4.3 Oil Seals

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Starter side:

- Remove the starter cup - see 6.3.

- Tap the oil seal with a suitablepiece of pipe or a punch torelease it from its seat.

• Apply the puller (1)5910 890 4400 (with No. 3.1jaws 0000 893 3706).

- Tension the arms.

- Pull out the oil seal.

Important : Take care not todamage crankshaft stub.

- Clean sealing surface with astandard solvent-based de-greasant containing no chlorina-ted or halogenated hydrocarbons- see 12.2.

- Lubricate sealing lips of oil sealwith grease - see 12.2.

• Slip installing sleeve (1) 4116893 4601 over the end of thecrankshaft.

- Push the oil seal, open sidefacing the crankcase, over theinstalling sleeve.


- Remove the installing sleeve.

- Fit the starter cup - see 6.3.

Always check and, if necessary,repair the fuel system, carburetor,air filter and ignition system beforelooking for faults on the engine.


- Remove the muffler - see 4.1.

- Remove the carburetor -see 8.2.2.

• Take the sleeve (1) out of themanifold.

• Take the washer (2) off the studs.

4.4 Exposin g the Cylinder

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- Preparations - see 4.4.

- Remove the spark plug.

- Unscrew the decompressionvalve.

• Unscrew the four cylinder basescrews through the holes in thecylinder.

• Carefully lift the cylinder up and,at the same time, push themanifold through the tankhousing opening.

- Pull the cylinder off the piston.

• Release the hose clamp (1).

• Pull the manifold (2) off theintake port.

- Inspect the cylinder and replaceit if necessary.

- If a new cylinder has to be instal-led, always fit the matchingpiston. New cylinders are onlysupplied complete with piston forthis reason.

- 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 thecrankshaft by sliding the woodenassembly block between thepiston and crankcase.

- Remove the cylinder gasket.

• Ease the hookless snap ringsout of the grooves in the pistons.

• Use the assembly drift (2)4116 893 4700 to push thepiston pin (1) out of the piston.

Note: If the piston pin is stuck, tapthe end of the drift lightly with ahammer if necessary.Important : Hold the pistonsteady during this process toensure that no jolts are transmittedto the connecting rod.

- Remove the piston and takethe needle cage out of theconnecting rod.

• Inspect piston rings and replaceif necessary - see 4.6.

4.5 Cylinder and Piston4.5.1 Remov al

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• Thoroughly clean the gasketseating surface (1).

• Lubricate the needle cage (2)with oil and fit it in the small end.

• Use the installing tool5910 890 2210 to fit hooklesssnap ring (2) in the forwardfacing piston boss - arrow (1)must point left.

• To ease assembly, heat thepiston slightly and slip it over theconnecting rod.

• Installed position of piston:1 = Arrow2 = Flywheel

• Push the assembly drift, smalldiameter (1) first, through thepiston and small end (needlecage) and line up the piston.

• Fit the piston pin (1) on theassembly drift (2) and slide it intothe piston (the pin slides homeeasily if the piston is heated).

• Use installing tool (1)5910 890 2210 to fit the snapring.

Note: For instructions on how touse installing tool, see "StandardRepairs, Troubleshooting" hand-book.

• Place new cylinder gasket inposition.

• Lubricate the piston and pistonrings with oil and place the piston(1) on the wooden assemblyblock (2) 1108 893 4800.

4.5.2 Installation

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• Install the new piston rings in thegrooves so that the radii at thering gap face upward and meetat the fixing pin.

• Push the manifold onto theintake port.

• Note installed position ofmanifold.

• Push the hose clamp over themanifold. The screw must behorizontal and the screw headmust point to the right.

• Tighten the screw until the gap"a" between the two ends of thehose clamp is 5 - 6 mm(0.20 - 0.24 in).

• Use the clamping strap (1)0000 893 2600 to compress thepiston rings around the piston.

- Check that the piston rings arecorrectly positioned.

- Lubricate the inside of thecylinder with oil and line it up sothat it is positioned as it will be inthe installed condition. It isimportant to observe this pointas the piston rings might other-wise break.

• Slide the cylinder over the piston- the clamping strap is pusheddownward as the piston ringsslip into the cylinder.

- Remove the clamping strap andwooden assembly block.

• To fit the manifold in the tankhousing intake opening, wind apiece of string (1) (about15cm/6" long) around the back ofthe manifold flange and pass theends of the string through theintake opening.

• Push cylinder towards tankhousing so that manifold flangelocates against intake opening.

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• Pull the ends of the stringoutward.

Note: The manifold flange is thuspulled through the tank housingintake opening without damagingthe manifold.

- Carefully line up the cylinder andgasket.

• Use socket (1) 0812 542 2104to tighten down cylinder basescrews to 9.5 Nm (7 lbf.ft).

Assembly is now a reversal of thedisassembly sequence.

- Remove the piston - see 4.5.1.

Note: The piston must beremoved to make sure that noresidue can fall into the crankcasewhen installing the piston ringsand cleaning their grooves.

- Remove rings from piston.

• Use a piece of old piston ringto scrape the grooves clean.

• Install the new piston rings in thegrooves so that the radii (1) facethe fixing pin (2).

- Install the piston - see 4.5.2.

- Remove the cylinder and usewooden assembly block 1108893 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.


• Remove cable guide (2) withthrottle cable (3).


• Remove the ignition module (2).

4.6 Piston Rings 4.7 Crankca se4.7.1 Cranksha ft

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FS 500, 550 17

• Pull the rubber boot (1) off thehigh-voltage output.

• Unscrew the ignition lead (2)from the contact pin and pull itout of the high voltage output.

- Slip the rubber boot off theignition lead.

• Ease the grommet (1) out of thetank housing.

• Pull ignition lead (2) out of thehousing.

• Remove upper fuel tank moun-ting screws.

• Remove lower fuel tank moun-ting screws.

- Take the crankcase off the fueltank.


- Remove the heat shield.

• Pull the impulse hose off theelbow connector.


• Mount the puller (1)4119 890 4600 to the clutch sideof the crankcase.

398R

A05

912

VA

398R

A06

1V

A

398R

A06

4V

A

398R

A06

2V

A

398R

A06

5 V

A

398R

A06

0

12

VA

398R

A06

3V

A

398R

A06

6

1

VA

18 FS 500, 550

• Turn thrust bolt clockwiseuntil the crankshaft is releasedfrom the ball bearing. The twohalves of the crankcase separatein this process.

- Remove the crankcase gasket.

• Press the crankshaft out of thestarter side of the crankcase.

• The crankshaft (1), connectingrod (2) and needle bearing forman inseparable unit. It mustalways be replaced as acomplete unit.

- When fitting a replacementcrankshaft always install new oilseals and ball bearings.

• Carefully knock the oil seal out ofthe clutch side of the crankcase.

• Use press arbor (1)1118 893 7200 to remove ballbearing.

• Pry the oil seal out of the starterside of the crankcase.

• Use press arbor (1)1118 893 7200 to remove ballbearing.

- Inspect both halves of the crank-case for cracks and replace ifnecessary.

Note: The complete crankcasemust be replaced even if only onehalf is damaged.

- If necessary, take the snap ringout of the crankcase.

398R

A06

7V

A

398R

A07

0 V

A

398R

A07

3

1

VA

398R

A06

8 V

A

398R

A07

1

1

VA

398R

A06

9

2

1

VA

398R

A07

2V

A

FS 500, 550 19

New crankcases come withfactory-installed ball bearings.

Stamp the machine number on thenew crankcase with 2.5 mm (0.1")figure stamps.

If the original crankcase is usedagain, remove the gasket residueand clean the mating surfaces -they must be cleaned verythoroughly to ensure a perfectseal.

• Check that dowel pins are inposition. If necessary, drive thepins into the crankcase.

- Heat area of bearing seat onclutch side of crankcase toapprox. 120°C (250°F).

• Fit ball bearing in crankcase byhand and push it home as far asstop.

Note: This operation must becarried out very quickly becausethe bearing absorbs heat immedi-ately and begins to expand.

• If it is not possible to heat theclutch side of the crankcase, usepress arbor (1) 1118 893 7200 topress in the ball bearing as faras stop.

• Check that snap ring is inposition in starter side of crankca-se or fit if necessary.

- Heat area of bearing seat onstarter side of crankcase toapprox. 120°C (250°F).

• Fit ball bearing, shoulder (1) first,in crankcase by hand and push ithome until it butts against thesnap ring.

Note: This operation must becarried out very quickly becausethe bearing absorbs heat immedi-ately and begins to expand.

• If it is not possible to heat thestarter side of the crankcase,use press arbor (1)1118 893 7200 to press in theball bearing as far as stop.

4.7.2 Installing Crankshaft

398R

A07

8

1

VA

398R

A07

4 V

A

398R

A07

6 V

A

1

398R

A07

5 V

A

398R

A07

7V

A

398R

A07

9

1

VA

20 FS 500, 550

- Use soldering iron with suitablecopper attachment to heat innerrace of ball bearing in clutch sideof crankcase to approx. 150°C(300°F).

• Push tapered stub of crankshaftsquarely into the ball bearing.

Note: This operation must becarried out very quickly becausethe crankshaft absorbs heat imme-diately and will not otherwise buttagainst the ball bearing.

• Wait for crankcase to cool down,then place a new gasket on themating face.

- Use soldering iron with suitablecopper attachment to heat innerrace of ball bearing in starterside of crankcase to approx.150°C (300°F).

• Position crankcase above thecrankshaft stub.

• Push the ball bearing squarelyover the crankshaft stub.

Note: This operation must becarried out very quickly becausethe crankshaft absorbs heat imme-diately and will not otherwise buttagainst the ball bearing.

• Insert screws and use socket (1)0812 542 2104 to tighten themdown to 9.5 Nm (7.0 lbf.ft).

- Lubricate sealing lips of oil sealswith grease - see 12.2.

• Fit installing sleeve (1)4116 893 2400 over the starterend of the crankshaft.

- Slide the oil seal, open sidefacing the crankcase, over theinstalling sleeve.


- Remove the installing sleeve.

398R

A08

0V

A

398R

A08

2V

A

398R

A08

4 V

A

1

398R

A08

3

1

VA

398R

A08

1V

A

398R

A03

1

1

VA

FS 500, 550 21

- Slide the oil seal, open sidefacing the crankcase, over theclutch end of the crankshaft.


Assemble all other parts in thereverse sequence.

- Tighten screws on heat shield to5.0 Nm (3.7 lbf.ft).

- Place cable guide with throttlecable in position, insert screwand tighten down to 4.5 Nm(3.3 lbf.ft).

- Install and adjust ignition module- see 5.2.2.

- Fit the tank housing - see 8.5.

- Remove the shroud- see 4.1.

• Use standard commercial long-reach 13 mm socket to unscrewthe decompression valve.

- Install new decompression valveand tighten down to 14 Nm(10.3 lbf.ft).

- Fit the shroud.

Warning! Exercise extremecaution when carrying outmaintenance and repair work onthe ignition system. The highvoltages which occur can causeserious or even fatal accidents!

Troubleshooting on the ignition sy-stem should always begin atthe spark plug. See "StandardRepairs, Troubleshooting" hand-book.

Note: The electronic (breakerless)ignition system basically consistsof an ignition module (1) andflywheel (2).

4.8 Decompressio n Valve 5. IGNITION SYSTEM

398R

A08

5

1

VA

398R

A08

6V

A

398R

A08

7

2

1

VA

22 FS 500, 550

- Remove the shroud - see 4.1.

• Pull grommet out of the tankhousing.

• Use pliers to grip the leg springand pull it out of the spark plugboot.

- Unhook the leg spring from theignition lead.

- Pull spark plug boot off theignition lead.

- Coat end of the ignition lead(about 20 mm/3/4") with oil.

- Fit spark plug boot over theignition lead.

• Use pliers to grip the end of theignition lead inside the sparkplug boot and pull it out.

• Pinch hook of leg spring into thecenter of the lead, i.e. about15 mm (9/16") from the end ofthe lead.

• Pull the lead back into theboot so that the leg springlocates properly inside it.

Important : If the spark plugcomes with a separate terminalnut, always fit the nut on thethread and tighten it downsecurely.

- Push grommet into the recess inthe tank housing.

- Fit the boot on the spark plug.

- Fit the shroud - see 4.1.

5.1 Spark Plug Boot

398R

A08

8V

A

398R

A09

0V

A

250R

A00

8 V

A

398R

A08

9V

A

398R

A09

1V

A36

6RA

104

VA

FS 500, 550 23

The ignition module accommoda-tes all the components required tocontrol ignition timing.

There are two electrical connecti-ons on the coil body:

1. the high voltage output (1)

2. the connector tag (3) for theshort circuit wire

Accurate testing of the ignitionmodule is only possible withsophisticated test equipment. Forthis reason it is only necessary tocarry out a spark test in the work-shop. A new ignition module mustbe installed if no ignition spark isobtained (after checking thatwiring and stop switch are ingood condition).

Ignition timing is not adjustable.

Since there is no mechanical wearin these systems, ignition timingcannot get out of adjustment. How-ever, an internal fault in the circuitcan alter the switching point insuch a way that a spark test willstill show the system to be in orderalthough timing is outside thepermissible tolerance. This willimpair engine starting and runningbehavior.

- Remove clutch housing -see 9.1.

- Ease ignition lead grommet outof recess in tank housing -see 5.1.

• Lever ignition lead out of guide incrankcase.

• Remove ignition lead from theretainers.

5.2 Igniti on Module 5.2.1 Ignitio n Timing 5.2.2 Remov ing and Insta lling

250R

A09

5

1

2V

A

398R

A09

3V

A39

8RA

094

VA

24 FS 500, 550

• Pull short circuit wire connector(1) off tag.

• Remove short circuit wire fromretainers (2).

• Ease lug of segment out ofcrankcase opening.

• Remove the segment.


- Remove the ignition module.

• Pull the rubber boot (1) off thehigh voltage output.

• Unscrew ignition lead (2) fromthe contact pin and pull it out ofthe high voltage output.

• Pull short circuit wire off theignition module.

- Pack the high voltage output withSTIHL multipurpose grease -see 12.2.

Important : Do not use a graphitegrease (Molykote) or siliconeinsulating paste.

- Screw ignition lead into highvoltage output.

- Slide rubber boot over the highvoltage output.

398R

A09

5

1

VA

2

2

398R

A09

8V

A

398R

A10

0V

A

398R

A09

6V

A

12

398R

A09

9V

A

398R

A09

7V

A

FS 500, 550 25

- Place the module in position,insert the screws but do nottighten them down yet.

Important : A washer must be fit-ted under each screw head.

• Slide the setting gauge (1)1127 890 6400 between thearms of the ignition module andthe flywheel magnet poles.

- Press the ignition moduleagainst the gauge and tightendown the mounting screws to atorque of 7.5 Nm (5.5 lbf.ft).

Reassemble all other parts in thereverse sequence.

- Fit ignition lead in the retainers.

- Remove the ignition module andtake the ignition lead out of thehigh voltage output - see 5.2.2.

• Pull the rubber boot off theignition lead.

• Pull the ignition lead out of thecrankcase.

• Remove the spark plug boot (1) -see 5.1.

• Pull the grommet (2) off theignition lead.

- Cut new ignition lead to length(see parts list or cut to samelength as old lead).

• Use a pointed tool (awl or gimlet)to pierce the center of the igni-tion lead at the end whichscrews into the module.

Reassemble all other parts in thereverse sequence.

5.3 Ignition Lead

VA

398R

A09

21 39

8RA

103

12

VA

398R

A10

1V

A

338R

A14

2 V

A

398R

A10

2V

A

26 FS 500, 550

- Remove the clutch - see 3.1.

- Remove segment from flywheel -see 5.2.2.

• Unscrew the flywheel nut.

• Screw the puller (1)1110 890 4500 into the flywheel.

• Screw home the thrust bolt untilthe flywheel is released.

• Pull off the flywheel.

Inspect the flywheel (1) andmagnet poles (2). If you find anydamage, install a new flywheel.

Instal ling the flyw heel:

Important: Clean the stub of thecrankshaft and the flywheel hubbore with a standard commercial,solvent-based degreasant whichcontains no chlorinated orhalogenated hydrocarbons -see 12.2.

• Make sure Woodruff key isproperly seated.

- Fit the flywheel.

Note: Check position of slot.

Assemble all other parts in thereverse sequence.

- Fit and tighten down flywheel nutto 30 Nm (22 lbf.ft).

- Remove clutch housing -see 9.1.

• Take out the screw (1).

• Remove top (2) of cable guide.

• Remove short circuit wire (1)from connector tag.


• Pull off the guide (1).


• Remove the short circuitcontact (3).

5.4 Flywheel 5.5 Shor t Circ uit Contact

398R

A10

4V

A

398R

A10

7

2

1

VA

398R

A12

1

1

2

VA

398R

A10

5V

A

1

398R

A10

8 V

A

398R

A10

9

2

1

VA

398R

A10

6V

A

398R

A11

0

1

2

3

VA

FS 500, 550 27

If the action of the starter ropebecomes very stiff and the roperewinds very slowly or not com-pletely, it can be assumed thatthe starter mechanism is in orderbut plugged with dirt. At very lowoutside temperatures the lubri-cating oil on the rewind spring maythicken and cause the springwindings to stick together. Thishas a detrimental effect on thefunction of the starter mechanism.In such a case it is sufficient toapply a few drops of paraffin(kerosine) to the rewind spring.

Then carefully pull out the starterrope several times and allow it torewind until its normal smoothaction is restored.

If clogged with dirt or pitch, theentire starter mechanism, inclu-ding the rewind spring, must be re-moved and disassembled. Takespecial care when removing thespring.

Wash all parts in paraffin or whitespirit.

Lubricate the rewind spring andstarter post with STIHL speciallubricant, see 12.2, beforeinstalling.

Troubleshooting chart - see"Standard Repairs, Trouble-shoo-ting" handbook.


• Remove the starter cover.

- Remove the rope rotor - see"Standard Repairs, Trouble-shoo-ting" handbook.

- Take out the screw and removeany remaining pieces of springfrom the starter cover.

Note: The replacement spring co-mes ready for installation withspring housing.

- It should be lubricated with a fewdrops of STIHL special lubricantbefore installation - see 12.2.

• Place the rewind with spring hou-sing (bottom facing up) in thestarter cover. Engage the outerspring loop as shown in the illu-stration (see arrow).

Cauti on: The rewind spring maypop out and uncoil duringinstallation.

- If the rewind spring has poppedout, refit it as follows:

• Position the outer spring loopabout 20 mm (3/4") from theedge of the spring housing(distance "a").

• Refit rewind spring in fan hou-sing in the clockwise direction,starting outside and workinginwards.

398R

A11

2 V

A

6. REWIND STARTER 6.2 Rewind Spr ing6.1 General 6.2.1 Replacing

398R

A11

1V

A

328R

A12

2

a

VA

398R

A12

3

1

VA

28 FS 500, 550

• Place the wooden assemblyblock (1) 1108 893 4800 acrossthe spring housing to simplifyrefitting.

• Check the position of the innerspring loop. It should be2 mm (0.08") away from the star-ter post.

- Install the rope rotor - see"Standard Repairs, Trouble-shooting" handbook.

- Tension the rewind spring -see 6.2.2.

- Make a loop in the starter rope.

• Push starter rope into notch inthe rotor.

• Grip the rope close to the rotorand use it to turn the rope rotorseven full turns counterclockwise.

• Hold the rope rotor steady.

• Pull out the rope with the startergrip and straighten it out.

- Hold the starter grip firmly tokeep the rope tensioned.

- Let go of the rope rotor andslowly release the starter ropeso that it can rewind properly.

Note: The rewind spring iscorrectly tensioned when the star-ter grip sits firmly in the rope guidebush without drooping to one side.If this is not the case, tension thespring by oneadditional turn.

When the starter rope is fullyextended, it must still be possibleto rotate the rope rotor at leastanother half turn before maximumspring tension is reached. If this isnot the case, pull the rope out,hold the rope rotor steady andtake off one turn of the rope.

Do not overtensi on the rewindspr ing as this will caus e it tobreak.

- Fit starter cover, insert screwsand tighten down to 4.5 Nm(3.3 lbf.ft).

6.2.2 Tensi oning

398R

A11

4 V

A39

8RA

115

VA

398R

A11

7V

A

398R

A11

3 V

A

a39

8RA

116

VA

FS 500, 550 29

- Remove the starter cover -see 6.2.1.

- Block piston with locking strip -see 3.1.

• Unscrew the nut (1).

• Pull off the starter cup (2).


- Tighten down nut to 24 Nm(17.7 lbf.ft).

• Take out screw and washer.

- Pull off the control handle.

Warning: To avoid risk of electricshock, do not start the unit whilethe control handle is open.

• Remove screws with screwdriver(1) 5910 890 2301.

- Separate the control handle.

• Lift the interlock lever (1) slightlyand turn it to one side until thetorsion spring (2) is relaxed.

• Pull the interlock lever off thepeg.

• Remove the torsion spring.

• Take the throttle trigger (1) withtorsion spring (2) and throttlecable (3) off the peg.

• Disconnect throttle cable fromtrigger.

Assemble in the reverse sequence.

398R

A11

8 V

A

1

2

6.3 Starter Cup 7. THROTTLE CONTROL7.1 Throttl e Trigger/Interl ock Lever

30 FS 500, 550

• Attach the throttle cable, thenposition torsion spring as shownand push its long arm into theslot.

• The interlock lever must bebehind the throttle trigger.

• Check correct positions ofthrottle cable (1), contact spring(2), protective tube (3) andinsulator (4).

- Remove the throttle trigger -see 7.1.

• Lift contact spring (1) a little andremove the throttle cable (2).

• Remove spring from recesses(1) and peg (2).

• Remove contact spring frompeg (1) and collar screw (2).

• Take out slide control’s collarscrew (1).

• Remove detent spring (2).

• Pull slide control out of handlemolding.

Assemble in the reverse sequence.

- Engage contact spring correctlyin groove of collar screw.

7.2 Contac t Spr ings /Detent Spr ing in Contr ol Handle

FS 500, 550 31

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.

• Disconnect throttle cable nipple(1) from slotted pin (2) on throttlelever.


• Remove top (2) of cable guide.

• Take throttle cable (1) out ofretainer (2) and guide (3) andpull it out of the tank housing (4).

- Adjust throttle cable - see 7.3.2.

• Throttle lever must butt againstthe idle speed screw’s holderwhen the throttle trigger is in thefull throttle position.

• On carburetors with an idlespeed screw: Throttle lever mustbutt against the idle speed screwwhen the trigger is in the idleposition.

- Check correct setting of idlespeed screw.

Important : Note adjustment rangeof idle speed screw.

7.3 Throttle Cable7.3.1 Replac ing 7.3.2 Adjusting

398R

A12

4

4

1

3

2

VA

398R

A12

5V

A

2

1

398R

A11

9V

A

398R

A12

6V

A

398R

A12

1

1

2

VA

32 FS 500, 550

• Slacken the screw.

- Squeeze the throttle trigger asfar as stop (full throttle), hold itthere and tighten down screw to1.0 Nm (0.75 lbf.ft).

- Release the throttle trigger (idleposition). The throttle lever mustbutt against idle speed screw’sholder, if fitted.

Dirty and clogged air filters reduceengine power, increase fuelconsumption and make startingmore difficult.

The air filter must be cleanedwhen there is a noticeable lossof engine power.

- Close the choke shutter.

- Clean away any loose dirt fromaround the filter and carburetorbox cover.

• Unscrew the nuts (1).

• Remove the carburetor boxcover (2).

• Take auxiliary filter out ofcarburetor box cover.

- Dry a wet auxiliary filter - thenshake it clean or blow it out withcompressed air.

- If the filter is heavily loaded withdirt or damaged, fit a new one.

• Remove the air filter.

- Wash the filter in a fresh, non-flammable cleaning solution (e.g.warm soapy water) and shakedry or, if possible, blow out withcompressed air.

- Soften encrusted dirt by soakingthe filter in cleaning solution.

- Always replace a damaged airfilter.

8. FUEL SYSTEM8.1 Air Filter

398R

A12

0V

A

398R

A12

7V

A

2

1

398R

A12

9V

A

398R

A12

8V

A

FS 500, 550 33

• Pull out the air diverterand clean it thoroughly.


• Inspect gasket in carburetor boxcover and replace if necessary.

- Tighten down nuts to 4.5 Nm(3.3 lbf.ft).

The carburetor can be tested forleaks with the carburetor andcrankcase tester 1106 850 2905.


• Pull fuel hose off carburetor’selbow connector.

• Fit fuel line (1) 1110 141 8600 onnipple (2) 0000 855 9200.

• Push the fuel line with nippleonto the carburetor elbowconnector.

• Push the nipple into the tester’spressure hose.

• Close the vent screw (1) on therubber bulb (2) and pump air intothe carburetor until the pressuregauge (3) shows a reading ofapprox. 0.8 bar (11.5 psi).

8.2 Carburetor8.2.1 Leakage Test

398R

A13

1V

A

398R

A13

3V

A

398R

A13

0V

A

398R

A13

2V

A

398R

A13

4V

A

143R

A17

2

2 1

VA

398R

A13

5

3

VA

2

1

34 FS 500, 550

If this pressure remains constant,the carburetor is airtight. However,if it drops, there are two possiblecauses:

1. The inlet needle is not sealing(foreign matter in valve seat orsealing cone of inlet needle isdamaged or inlet control leversticking).

2. The metering diaphragm isdamaged.

In either case the carburetor mustbe removed and serviced - see"Carburetor" handbook.

- After completing test, open thevent screw and pull the fuel lineoff the elbow connector.

- Push the fuel hose onto theelbow connector.

- Install the air filter - see 8.1.


Important: In the event of troublewith the carburetor or the fuelsupply system, always check andclean the tank vent - see 8.3.


• Pull fuel hose off carburetor’selbow connector.

• Push retaining rib (1) upward.

• Pull choke knob (2) off the shaft.

• Disconnect manual fuel pumphose from the carburetor.

• Disconnect throttle cable nipple(1) from slotted pin (2) on throttlelever.

- Remove the fuel filler cap.

• Ease the grommet off theadjusting screws and take it outof the tank housing.

8.2.2 Removin g and Instal ling

398R

A13

7V

A

398R

A13

2V

A

398R

A13

8

1

VA

2

1

2

398R

A13

6V

A

398R

A13

9V

A

FS 500, 550 35

• Take out the screws (1) andunscrew the nuts (2).

• Remove the backing plate (3).

• Pull impulse hose off the elbowconnector.

• Pull carburetor off the studs.


• Check that sleeve (1) is inmanifold and washer (2) is inposition.

- Tighten down screws on backingplate to 6.5 Nm (4.8 lbf.ft) andnuts to 5.5 Nm (4 lbf.ft).

The machines are equipped withan electronic speed limiter thatoperates via the ignition system.

Therefore, the carburetor cannotbe adjusted to increase themaximum engine speed beyondthe preset limit.

Similarly, the machine cannot betuned for "best performance" byway of engine speed.An excessively lean carburetorsetting increases neither theengine speed nor its performance,it simply increase the risk ofengine damage.

Standard setting

If the carburetor has to beadjusted from scratch, first carryout the standard setting.

- Carefully screw in both adjustingscrews clockwise until they arehard 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

8.2.3 Adjusting

398R

A14

0V

A

1 2

3

1

2

398R

A02

1V

A

2

1

398R

A14

1V

A

398R

A14

3

1

VA

2

398R

A14

2V

A

36 FS 500, 550

A slight correction to this settingmay be necessary at high altitudes(mountains) or near sea level. Usethe following procedure:

- Mount approved cutting tool.

- Check the air filter, replace ifnecessary.

- Check spark arresting screen,clean or replace as necessary.

- Start the engine and allow it towarm up.

Turn high speed screw (H)clockwise for leaner mixture athigh altitude,or counterclockwise for richermixture at sea level.

Turn screw slowly and carefully –slight changes have a noticeableeffect 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 beginsto rotate, and then turn screw backone half turn.

Cutting tool rotates whileengine is idling:

- Carry out standard setting.

Turn the idle speed screw (LA)counterclockwise until cutting toolstops rotating – and then turn itabout another half turn in thesame direction.

Correct operation of the carburetoris only possible if atmosphericpressure and internal fuel tankpressure are equal at all times.This is ensured by the tank vent.

Important: If problems occur onthe carburetor or the fuel supplysystem, always check and cleanthe tank vent.

Check function by performingpressure and vacuum tests onthe tank via the fuel hose.

Equalization of pressure

Equalization of pressure from theoutside inwards takes place viathe hole in the fuel filler cap, thesintered filter, the valve and holesin the cap.

Equalization of pressure from theinside outwards takes place viathe holes in the cap, the hole inthe valve body, the sintered filterand the hole in the fuel filler cap.

8.3 Tank Vent

398R

A14

5V

A39

8RA

146

VA

398R

A14

4

3

VA

FS 500, 550 37

Cleaning

- Unscrew the fuel filler cap.

• Ease the cap (1) off the valvebody (2).

• Take sintered filter (3) out of cap.

• Pry valve body out of fuel fillercap (4).

• Pry sintered filter (5) out of fuelfiller cap.

- Wash valve body in cleangasoline.

• If diaphragm in the valve (6) isdamaged, pull it out of valvebody and fit new one.

• Push new sintered filter (5) intofiller cap.

• Fit sealing ring (7) over valvebody.

- Fit valve body in filler cap andpress it home until it snaps intoposition.

- Fit new sintered filter in the cap.

- Fit cap on valve body and pressit down until it snaps into position.

- Refit the fuel filler cap.

The diaphragm pump draws fuelout of the tank and into thecarburetor via the fuel hose. Anyimpurities mixed with the fuel areretained by the pickup body (filter).The fine pores of the filter event-ually become clogged with minuteparticles of dirt. This restricts thepassage of fuel and results in fuelstarvation.

Important: In the event of troublewith the fuel supply system,always check the fuel tank andthe pickup body first. Clean thefuel tank if necessary.

Cleaning the fuel tank

- Unscrew the filler cap and drainthe tank.

- Pour a small amount of cleangasoline into the tank.

- Close the tank and shake theunit vigorously.

- Open the tank again and drain it.

Note: Dispose of fuel properly.

Picku p body


• Pull the fuel hose (1) off theelbow connector.

• Pull hose (2) off the manual fuelpump.

• Ease the grommet out of thetank housing.

• Remove the fuel hoses withpickup body.

• Pull the pickup body off the fuelhose.

8.4 Picku p Body /Fuel Hoses

398R

A14

7

4

7

5

6

2

3

1

VA

398R

A14

9 V

A39

8RA

150

VA

398R

A14

8V

A

2

1

398R

A15

1 V

A

38 FS 500, 550

• Remove the cap (1).

• Remove the filter (2) and fit anew one.

Fuel hoses

- Pull off the pickup body.

• Pull fuel hoses out of thegrommet.


• Pass fuel hoses through thegrommet so that distance "a"is 65 ± 1 mm (2.55 in),and "b" is 40 ± 1 mm (1.57 in).

- Drain the tank housing.

- Remove the shroud - see 4.1.

- Remove the carburetor, take outthe sleeve and washer -see 8.2.2.

- Pull grommet with ignition leadout of tank housing - see 5.1.


• Remove screws from underside.

• Pull away the tank housing andpush the manifold flange out ofthe intake opening at the sametime.

• Take out the air diverter (1)and remove the manual fuelpump (2) and grommet (3) withfuel hoses.

• Pull the cover out of it mounts.

8.5 Tank Housi ng

328R

A21

9 V

A

1 2

VA

398R

A15

6

398R

A15

2 V

A

398R

A15

4V

A

1

2

3

398R

A15

7V

A

398R

A15

3

b

a

VA

398R

A15

5V

A

398R

A15

8V

A

FS 500, 550 39


- Place tank housing in position.

• Pass throttle cable (1) andimpulse hose (2) through the bo-res.

• To fit the manifold in the tankhousing intake opening, wind apiece of string (1) (about 15cm/6" long) around the back of themanifold flange and pass theends of the string through theintake opening.

• Push tank housing towardscylinder so that manifold flangelocates against intake opening.

• Pull the ends of the stringoutward.

Note: The manifold flange is thuspulled through the tank housingintake opening without damagingthe manifold.

Important: There must be nointernal stresses in the tankhousing when the seven screwsare tightened down.

- To avoid this, screw home thethree side screws only fingertightfirst.

- Then push the crankcase andunderside of the tank housingfirmly together.

- Insert the four screws in theunderside and tighten themdown to 5.5 Nm (4 lbf.ft).

- Finish off by tightening downthe three side screws to 5.5 Nm(4 lbf.ft).


• Disconnect hoses fromconnectors.

• Carefully push back the retainingtabs.

• Pull fuel pump out of its seat inthe tank housing.

Install in the reverse sequence.

8.6 Manual Fuel Pump

398R

A15

9V

A12

3

VA

398R

A16

039

8RA

161

VA

398R

A16

2V

A

398R

A05

3V

A

40 FS 500, 550

The anti-vibration (AV) connectionbetween the engine and drive tubeconsists of four rubber buffers(annular buffers) and two stopbuffers in the AV housing.

- Remove the drive tube -see 10.3.

- Remove the bike handle - 10.1.

• Ease locking tabs of cover stripout of the AV housing.

- Remove the cover strip.


Note: Fourth screw not visible inthis view.

- Remove the clutch housing.

• Pry the plugs out of the annularbuffers.


- Remove the clutch housing.

• Pry the annular buffers out of theclutch housing.


- Remove the two halves of theclamp.

• Push the annular buffers out oftheir seats in the AV housing.


- Separate the two halves of theAV housing.

9. AV SYSTEM9.1 Repair

398R

A16

7V

A

398R

A16

5V

A

398R

A16

3V

A

398R

A16

8V

A

398R

A16

6V

A

398R

A16

4V

A

398R

A17

0V

A

398R

A16

9V

A

FS 500, 550 41

• Take the stop buffers out of thehousing moldings.

• To replace the upper half of thehousing, take out the screws (1).

• Remove the perforated rail (2).

• To replace the nut (1), removeshakeproof washer (2) with thenut.


• Insert annular buffer, smalldiameter first, from the clutchside until its groove (1) engagesthe housing rib (2).

- Tighten down AV housingscrews to 4.5 Nm (3.3 lbf.ft).

- Tighten down screws onperforated rail to 4.5 Nm(3.3 lbf.ft).

- Tighten down screws in annularbuffers in the clutch housing to3.5 Nm (2.6 lbf.ft).

• Plugs (2) have to be fitted in theannular buffers (1) in the AV hou-sing - press them home as far ascenter.

• Install annular buffers so thatthe housing rib (1) locates in thecenter groove (2).

- Do not tighten the screws in thetwo halves of the clamp until thedrive tube has been fitted -see 10.3.

- Tighten down clutch housingscrews to 9.5 Nm (7 lbf.ft).

398R

A17

1V

A

398R

A17

4

12

VA

398R

A17

6

1

2

VA

398R

A17

3

2

1

VA

398R

A17

2

2

1

VA

398R

A17

5

1

2 VA

42 FS 500, 550

- Remove the control handle -see 7.1.


• Remove bike handle (2) withclamp (3).

• Take out the screws (4).

• Remove the top and base ofclamp (3).

• Use jaws (1) 5910 893 2700 toclamp bike handle tube in vice.

- To replace left grip, carefully cutit open and pull it off.

- Coat inside of new grip with alittle lubricant (e.g. washing-upliquid).

Note: If too much lubricant isused, the grip will twist on thetube. Always leave it to dry for awhile after fitting.

• Take out the screws (1), removeclamp moldings (2) and shorttube (3).

Assemble all parts in the reversesequence.

- Tighten down screws on bikehandle clamp to 4.5 Nm(3.3 lbf.ft) and screws of clampmoldings on short tube to 4 Nm(3 lbf.ft).

The drive shaft is supported in aflexible liner inside the drive tube.The ends of the drive tube are sea-led with plugs.

- Remove the gearhead - see 11.1.

Driv e shaft

• Pull the drive shaft out of thedrive tube.

Note: If the shaft has turned blue,fit a new one.

- Coat the drive shaft with STIHLgear lubricant 0781 120 1109,see 12.2, before installation.

Important : Apply the greaseuniformly and thinly to the wholedrive shaft. Do not pump greasedirectly into the drive tube.

- Push the drive shaft into the dri-ve tube.

10. SHAFT 10.2 Driv e Shaft/10.1 Bike Handle Flexibl e Liner

398R

A17

7

1 3

2

4

VA

398R

A17

81

2

3

VA

FS 500, 550 43

• Push the drive shaft into the dri-ve tube until dimension "A" is 25mm/1". If necessary, apply slightpressure to the shaft and rotate itslowly until it can be pushed in tothe specified dimension.

- Fit the gearhead - see 11.1.

Flexibl e liner

- Remove the drive tube -see 10.3.

• Pry the plug out of the drive tube.

• Pull out the flexible liner.

• Fit the flexible liner into the driveso that the ’spokes’ point coun-terclockwise, viewed from the ge-arhead.

- Push flexible liner about 27 mm(1.1") into the drive tube.

- Insert the plug.

- Install the drive tube - see 10.3.

• Slacken off screws on clamp.

• Take the fixing screw (1) out ofthe clutch housing.

• Release the clamp screw (2).

• Pull the drive tube out of theclutch housing and the AVhousing.

10.3 Driv e Tube

398R

A17

9

A

VA

398R

A18

1V

A

398R

A18

2V

A

398R

A18

9V

A

398R

A18

3

2

VA

1

398R

A18

4V

A

398R

A18

0V

A

44 FS 500, 550

- Remove the drive shaft orflexible liner - see 10.2.


- Degrease clamp mounting area.

• Push home drive tube until theholes line up.

Note: Drive tube is shownnext to AV housing to illustrateposition of hole.

- Push home the drive tube andturn gearhead output shaft backand forth at the same time sothat square end of drive shaftengages the square socket indrive pinion.

- Tighten down centering screw to4.5 Nm (3.3 lbf.ft) and clampscrew to 8.0 Nm (5.9 lbf.ft).

- Tighten down screws on clampto 7.5 Nm (5.5 lbf.ft).

• Release clamp screws.

- Pull gearhead off the drive tube.

- Degrease clamp mounting area.

- Slide the gearhead onto the dri-ve tube and turn output shaftback and forth at the same timeso that square end of drive shaftengages the square socket in dri-ve pinion.

- Push the gearhead as far asstop and line it up.

- Tighten down clamp screws to10 Nm (7.5 lbf.ft).

- Remove the gearhead - see 11.1.

- Remove the deflector or limitstop - if fitted.

- Remove the grass shield - iffitted.

• Use pliers (2) 0811 641 8380to remove retaining ring (1).

• Remove the spacer washer (3).

• Take out the grub screw.

11. CUTTING TOOL DRIVE11.1 Gearhead 11.1.1 Disassembling

398R

A18

5V

A

398R

A18

6V

A

398R

A18

7

2

VA

1

3

398R

A18

8V

A

FS 500, 550 45

- Heat gear housing to approx.180-200°C (350-390°F andremove parts from input endof gearhead first and then theoutput end by knocking it againsta wooden base.

• Press the output shaft out of theball bearing.

• Use pliers (1) 0811 611 8200 toremove retaining ring from drivepinion.

• Use drift (1) 1108 893 4700 todrive pinion out of ball bearing.

- Remove spacer washer, if fitted,from the drive pinion.

- Clean all parts and check theirserviceability.

Note: Drive shaft with bevel gearand drive pinion can only bereplaced as a complete assembly(set of pinions).

• Slip spacer washer (1), if it wasoriginally fitted, over the drivepinion (2).

• Heat ball bearing (3) to approx.50°C (120°F) and push it on asfar as stop.

- Fit retaining ring in the groove.

• Heat ball bearing to approx.50°C (120°F) and push it on tooutput shaft as far as stop.

398R

A19

0V

A

398R

A19

2

1

VA

398R

A19

3

13

2

VA

398R

A19

4V

A

398R

A19

1

1

VA

11.1.2 Assembling

46 FS 500, 550

- Heat gear housing to approx.180-200°C (350-390°F).

• Place ball bearing (1) in housingand press it home as far as stopwith the press arbor (2)4116 893 7205 and installingsleeve (3) 1114 893 4601.

Note: Installing sleeve is usedonly as an extension.

• Place preassembled output shaftin the housing.

• Use installing sleeve (1)1119 893 2401 to press outputshaft into housing as far as stop.

• Place preassembled drive pinion(1) in the housing.

• Use press arbor (2) 4116 8937200 and installing sleeve (3)1114 893 4601 to press homedrive pinion as far as stop.

Important: Check that teeth ofpinions engage properly duringinstallation process.

Note: Installing sleeve is usedonly as an extension.

- Coat grub screw with Loctite -see 12.2.

- Insert grub screw in the housingand tighten it down to 4.5 Nm(3.3 lbf.ft).

Note: If pinion shaft bearing is pro-perly seated, the cone of the grubscrew should be visible inthe neck of the gearhead.

• Install the spacer washer, if itwas originally fitted.

1

2

3

398R

A19

5V

A

398R

A19

7

1

VA

398R

A19

9V

A

398R

A19

8

1

2

3

VA

398R

A19

6V

A

398R

A20

0V

A

FS 500, 550 47

• Install the retaining ring.

- Check running clearance (rotateoutput shaft), add or removeshim as necessary.

- Remove screw plug from gearhousing and pack gear housingwith grease.

Note: Use STIHL gear lubricant0781 120 1117 to lubricate thebevel gear drive - see 12.2.

Important : Pack gear housingwithabout 20 g (3/4 oz) grease.

Servic e note:

When carrying out maintenancework, add grease (max. 5 - 10 g/1/4 oz) only if no grease can beseen on the inside of the screwplug.

- Unscrew the tube of grease.

- Refit the screw plug and tightenit down to 10 Nm (7.5 lbf.ft).

- Refit the grass shield, if fitted.

- Refit the deflector or stop, if fitted.

- Remove the clutch housing -see 9.1.

• Use pliers (1) 0816 610 1495 toremove the retaining ring fromstub of clutch drum.

• Use drift (1) 1108 893 4700 topress the clutch drum out of theball bearing.

• Use pliers (1) 0811 641 8380 totake retaining ring out of clutchhousing.

• Remove ball bearing from clutchhousing with press arbor (1)1118 893 7200.


• Use press arbor (1) 1118 8937200 to press home ball bearingas far as stop.

• Press home clutch drum as faras stop with drift (1)1108 893 4700.

- Install the clutch housing -see 9.1.

11.2 Clutc h Drum

398R

A20

1V

A

398R

A20

2

1

VA

398R

A20

5

1

VA

398R

A20

31

VA

398R

A20

6

1

VA

398R

A20

4

1

VA

398R

A20

7

1

VA

48 FS 500, 550

No. Part Name Part No. Application Rem.

1 Locking strip for piston 0000 893 5903 Blocking crankshaft2 Press sleeve 1108 893 2405 Fitting oil seal3 Installing sleeve 4116 893 4601 Protecting oil seal

(starter side)4 Puller 5910 890 4400 Removing oil seals 1)5 - Jaws (No. 3.1 + 4) 0000 893 37066 Puller 1110 890 4500 Releasing flywheel7 Crimping tool 5910 890 8210 Attaching connectors to

electrical wires8 Assembly drift 4116 893 4700 Removing and fitting piston pin,

removing and installingclutch drum

9 Clamping strap 0000 893 2600 Compressing piston rings10 Wooden assembly block 1108 893 4800 Fitting piston11 Carburetor and 1106 850 2905 Testing carburetor

crankcase tester for leaks12 Vacuum pump 0000 850 3501 Testing crankcase for leaks13 - Nipple 0000 855 920014 - Fuel line 1110 141 860015 Sealing plate 0000 855 8106 Sealing exhaust port for

leakage test16 Test flange 1128 850 4200 For leakage test17 Setting gauge 1127 890 6400 Setting air gap between ignition

module and flywheel18 Socket, 13 mm 5910 893 5608 Screws for clutch,

flywheel nut andunscrewing starter cup

19 Torque wrench 5910 890 0301 0.5 - 18 Nm 5)(0.4 - 13.5 lbf.ft)

5910 890 0302 3)20 Torque wrench 5910 890 0311 6 - 80 Nm 5)

(4.4 - 60 lbf.ft)5910 890 0312 3)

21 Spline screw socket T27x125 0812 542 2104 IS screws22 Installing tool 5910 890 2210 Installing hookless snap rings

in piston23 Press arbor 1118 893 7200 Removing and installing ball bearings24 Puller 4119 890 4600 Removing crankshaft25 Circlip pliers 0816 610 1495 External circlip on

clutch housing26 Circlip pliers C19 0811 641 8380 Internal circlip in

clutch housing and gearhead27 Circlip pliers A10 0811 611 8200 External circlip on drive

pinion

12. Special Servicing Tools and Aids12.1 Special Servicing Tools

FS 500, 550 49

No. Part Name Part No. Application Rem.

28 T-handle screwdriver QI-T27x150 5910 890 2400 For all IS screws 4)29 Screwdriver T20x100 5910 890 2301 Separating handle moldings30 Assembly drift 1108 893 4700 Removing and installing

clutch drum, pressing drivepinion out of ball bearing

31 Press arbor 4116 893 7205 Installing ball bearing ingear housing

32 - Installing sleeve 1114 893 460133 Press arbor 4116 893 7200 Installing preassembled

drive pinion in gear housing34 Press sleeve 1119 893 2401 Installing preassembled

output shaft in gear housing35 Press arbor 1118 893 7200 Removing and installing

ball bearing in clutch housing36 Vice jaws 5910 893 2700 Holding drive tube and bike

handle37 Assembly stand 5910 890 3100 Holding FS units38 - 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 FSunits for repairs(in conjunction with assembly stand)

Remarks:

1) Equivalent to puller 0000 890 4400, but with longer spindle 5910 890 8400.2) Always use torque wrench to tighten DG/P screws.3) Wrench has optical/acoustic signal.4) On DG/P screws, use for releasing only.

50 FS 500, 550

No. Part Name Part No. Application

1 Lubricating grease 0781 120 1111 Oil seals(370 g/13 oz tube)

2 Standard commercial, Cleaning crankshaft stubsolvent-based degreasantcontaining no chlorinated orhalogenated hydrocarbons

3 STIHL special lubricant 0781 417 1315 Bearing bore in rope rotor,rewind spring in rope rotor

4 Ignition lead HTR (10 m/33’) 0000 930 2251

5 Medium-strength 0786 111 1101 Grub screw in gearhead,threadlocking (Loctite 242) annular buffers in AV housing

6 STIHL gear lubricant Drive shaft in drive tube- 80 g/3 oz tube: 0781 120 1109- 225 g/8 oz tube: 0781 120 1110

7 STIHL gear lubricant Gearhead lubrication- 80 g/3 oz tube: 0781 120 1117- 225 g/8 oz tube: 0781 120 1118

12.2 Servicing Aids

FS 500, 550 51

STIHL FS 500, 550 CONTENTS 2 5. Ignition System 22 9. AV...

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