STIHL 029, 039 1

STIHlSTIHlSTIHlSTIHl 1992 Andreas Stihl. Waiblingen

Service Manual029 and 039Chain Saws

As the design concept of these twomodels is almost identical, thedescriptions and servicing pro-cedures in this manual generallyapply to both. Differences aredescribed in detail.

You should make use of theillustrated parts lists while carryingout repair work. They show theinstalled positions of the individualcomponents and assemblies.Microfilmed parts list are alwaysmore up to date than printed lists.

A fault on the machine may haveseveral causes. Consult the"Troubleshooting Charts" whentracing faults.

Refer to the "Technical Informa-tion" bulletins for engineeringchanges which have been intro-duced since publication of thisservice manual.

Service manuals and technicalinformation bulletins describingengineering changes are intendedexclusively for the use of STIHLservicing dealers and staff andmust not be passed on to thirdparties.

Chain saw on assembly stand

The STIHL Special Tools manuallists all special servicing toolscurrently available from STIHL.

Always use original STIHLreplacement parts.Original STIHL parts can beidentified by the STIHL partnumber, the STIHlSTIHlSTIHlSTIHl logo andthe STIHL parts symbol ( Thesymbol may appear alone on smallparts.

Servicing and repairs are madeconsiderably easier if the saw ismounted on assembly stand 5910850 3100 or 5910 890 3100. Thisenables the saw to be swivelled tothe best position for the ongoingrepair and leaves both hands free.

The saw can be quickly secured tothe stand by means of the barmounting studs and nuts (afterremoving the sprocket cover).

STIHL 029, 039 2

CONTENTS

1. Specifications 3 5. Ignition System 37 11. Fuel System 58

1.1 Engine 3 5.1 Repairing Component 11.1 Air Filter 581.2 Fuel System 4 Parts 37 11.2 Removing and Installing1.3 Ignition System 4 5.1.1 Spark Plug 37 the Carburetor 591.4 Cutting Attachment 5 5.1.2 Ignition Module 39 11.3 Leakage Testing1.5 Special Accessories 5 5.1.2.1 Ignition Timing 39 the Carburetor 601.5.1 For User 5 5.1.2.2 Removing and Installing 39 11.4 Servicing the1.5.2 For Service 5 5.1.3 Spark Plug Terminal 41 Carburetor 601.6 Tightening Torques 6 5.1.4 Ignition Lead 42 11.5 Carburetor Adjustment 66

5.1.5 Flywheel 42 11.6 Automatic Choke 682. Troubleshooting 5.1.6 Short Circuit Wire/ 11.6.1 Description of Operation 68

Charts 7 Ground Wire 44 11.6.2 Troubleshooting Chart 695.1.7 Contact Spring 44 11.6.3 Testing Automatic

2.1 Clutch, Chain Drive, Choke 70Chain Brake and 6. Rewind Starter 45 11.6.4 Leakage TestingChain Tensioner 7 Engine Housing

2.2 Engine 8 6.1 Routine Maintenance 45 and Control Valve 702.3 Ignition System 9 6.2 Rope Rotor/Pawl 45 11.6.5 Testing Control Valve2.4 Rewind Starter 10 6.3 Replacing the (removed from machine) 712.5 Chain Lubrication 11 Starter Rope 46 11.6.6 Leakage Testing2.6 Fuel System 12 6.4 Replacing the the Bellows 72

Rewind Spring 47 11.6.7 Foam Filter/3. Clutch, Chain Drive, 6.5 Tensioning the Polymer Sintered Filter 72

Chain Brake and Rewind Spring 47 11.6.8 Removing and InstallingChain Tensioner 14 6.6 Replacing Starter the Carburetor 73

Rope Guide Bush 48 11.6.9 Removing and Installing3.1 Clutch Drum and Lever System on

Chain Sprocket 14 7. AV Handle System 49 Carburetor 733.2 Clutch 15 11.6.10 Throttle Shaft/3.3 Chain Brake 17 7.1 Repair 49 Choke Shaft 763.3.1 Disassembly 17 11.6.11 Hose/Connector 773.3.2 Assembly 19 11.6.12 Control Valve 773.4 Front Chain 8. Handle Housing 50 11.6.13 Bellows 78

Tensioner 21 11.7 Tank Vent 793.5 Side Chain 8.1 Front Handle 50 11.8 Fuel Pickup Body and

Tensioner 21 8.1.1 Removing and Installing Fuel Hose 793.6 Bar Mounting Studs 22 Handle Housing 50 11.9 Replacing the

FuelTank 804. Engine 23 9. Master Control 53

12. Special Servicing 824.1 Removing and Refitting 9.1 Switch Shaft 53 Tools and Aids

Exhaust Muffler 23 9.2 Interlock Lever/4.2 Leakage Testing Throttle Trigger 54 12.1 Special Servicing Tools 82

the Engine 24 12.2 Servicing Aids 834.2.1 Preparations 24 10. Chain Lubrication 554.2.2 Pressure Test 254.2.3 Vacuum Test 26 10.1 Suction Hose/4.3 Replacing the Pickup Body 55

Oil Seals 27 10.2 Vent Valve 564.4 Removing and Installing 10.3 Removing and Installing

the Engine 29 the Oil Pump 564.5 Cylinder 30 10.4 Servicing the4.6 Piston 33 Oil Pump 574.7 Piston Rings 354.8 Crankshaft 36

STIHL 029, 039 3

1. SPECIFICATIONS

1.1 Engine 029 039

STIHL single-cylinder two-stroke engine with specialimpregnated cylinder bore

Displacement: 54.1 cm3 (3.3 cu.in) 64.1 cm3 (3.9 cu. in)Bore: 45 mm (1.77 in) 49 mm (1.93 in)Stroke: 34 mm (1.34 in) 34 mm (1.34 in)Compression ratio: 9.5:1 10:1Power output: 2.70 kW (3.7 bhp) 3.20 kW (4.4 bhp)Max. torque: 2.8 Nm (2.1 lb. ft) 3.4 Nm (2.5 Ib. ft)

at 6,500 r.p.m. at 6,500 r.p.m.Max. permissible enginespeed with bar and chain: 13,000 r.p.m. 13,000 r.p.m.Mean idle speed: 2,700 r.p.m. 2,700 r.p.m.Crankshaft: Three-part, Three-part,

drop forged drop forgedCrankshaft bearings: 2 ball bearings 2 ball bearingsCrankpin dia.: 14.4 mm (0.55 in) 14.4 mm (0.55 in)Big-end bearing: Needle cage Needle cageConrod length: 58 mm (2.28 in) 58 mm (2.28 in)Piston pin diameter: 10 mm (0.39 in) 10 mm (0.39 in)Small-end bearing: Needle cage Needle cageRewind starter: Pawl system with Pawl system with

automatic rope automatic roperewind mechanism rewind mechanism

Starter rope: 3.5 mm (0.14 in) dia., 3.5 mm (0.14 in) dia.,960 mm (37.8 in) long 960 mm (37.8 in) long

Clutch: Centrifugal clutch Centrifugal clutchwithout linings, without linings,76 mm (3.0 in) dia. 76 mm (3.0 in) dia.

Clutch engages at: approx. 3,500 r.p.m. approx. 3,500 r.p.m.Crankcage leakage testat gauge pressure: 0.4 bar (5.8 psi) 0.4 bar (5.8 psi)under vacuum: 0.4 bar (5.8 psi) 0.4 bar (5.8 psi)

STIHL 029, 039 4

1.2 Fuel System 029 / 039

Carburetor: All position diaphragmcarburetor with integral fuelpump

Standard settingHigh speed adjusting screw H: Back off approx. 1 turnLow speed adjusting screw L: Back off approx. 1 turn

(starting with screws tightagainst their seats)

Carburetor leakage testat gauge pressure: 0.4 bar (5.8 psi)Fuel tank capacity: 0.56 L (1 .2 US pt)Fuel mixture: Regular brand-name gasoline

and brand-name two-strokeengine oil

Mix ratio: 50:1 with Stihl two-strokeengine oil25:1 with other brand-nametwo-stroke brand-name,air-cooled engine oils

Air filter: Prefilter (coarse filter)bisectional box filter

1.3 Ignition System

Type: Electronic magneto ignition(breakerless) with integraltrigger unit

Air gap: 0.15-0.3 mm (0.006-0.012 in)Ignition timing: 2.0-2.8 mm (0.08-0.10 in) B.T.D.C.

at 8,000 r.p.m.Advance angle: 24.5-29.5 B.T.D.C.

at 8,000 r.p.m.Spark plug (suppressed): Bosch WSR 6 F or

NGK BPMR 7 AElectrode gap: 0.5 mm (0.020 in)Spark plug thread: M14x1.25Length of thread: 9.5 mm (0.37 in)Heat range: 200

STIHL 029, 039 5

1.4 Cutting Attachment

Guide bars: Rollomatic with sprocket noseDuromatic with stellite-tipped nose

Bar tail: 3003

Bar lengths: (32, 37, 40, 45, 50 and 63 cm)(13, 15, 16, 18 and 25 in)

Oilomatic chain: 9.32 mm (3/8") Rapid-Micro,Rapid-Super8.25 mm (0.325") Rapid-Micro,Rapid-Super

Chain sprockets: 7-tooth 3/8" spur sprocket7-tooth 0.325" spur sprocket7-tooth 0.325" rim sprocket8-tooth 0.325" rim sprocket

Chain speed: 21.7 m/s (71 ft/s) at 10,000 r.p.m.

Chain lubrication: Fully automatic, speed-controlledreciprocating oil pump, no feed atidle speed. Additional manual oil flowcontrol

Oil feed rate (adjustable): 6-15 cm/min (0.2 - 0.5 fl.oz/min)at 10,000 r.p.m.

Oil tank capacity: 0.33 L (0.7 US pt)

1.5 Special Accessories

1.5.1 For user STIHL repair kit 1127 900 5000Starter rope 3.5x30.5 m 0000 930 22037-tooth 3/8" rim sprocket kit 1125 007 10027-tooth 0.325" rim sprocket kit 1125 007 10018-tooth 0.325" rim sprocket kit 1125 007 10007-tooth 3/8" spur sprocket 1125 640 20007-tooth 0.325" spur sprocket 1125 640 2005Spur gear/tensioning screw kit 1127 007 1003Elastostart 1128 190 3400

1.5.2 For service shop Carburetor parts kit (Walbro) 1127 007 1060Carburetor parts kit(automatic choke) 1127 007 1061

STIHL 029, 039 6

1.6 Tightening Torques

"DG" screws are used in the polymer and light-alloy components of models 029 and 039. When screwed in for thefirst time, DG screws form a permanent thread in the parts concerned. They can be released and retightened as oftenas necessary without affecting the strength of the screwed assembly. However, it is essential to always use a torquewrench to tighten the screws to the specified torques.

Fastener Thread For component Torque Remarkssize Nm (Ibf.ft)

Spline screw IS-DG4x15 Chain tensioner cover/engine housing 3.2 (2.4)

Spline screw IS-DG4x15 Chain brake cover/engine housing 3.2 (2.4)

Spline screw IS-DG4x15 Handle housing/handle molding 1.6 (1.2)Spline screw IS-DG4x15 Oil pump 4.0 (3.0)Spline screw IS-DG4x15 Shroud/engine housing 3.2 (2.4)Spline screw IS-DG4x15 Ground wire to cylinder 4.0 (3.0)Spline screw IS-DG5x16 Chain catcher/engine housing 3.5 (2.6)Spline screw IS-DG5x16 Spiked bumper/engine housing 3.5 (2.6)Spline screw IS-DG5x24 Front handle/handle housing 3.5 (2.6)Spline screw IS-DG5x24 Hand guard (I/h) with sleeve 3.5 (2.6)Spline screw IS-DG5x24 Fan housing/engine housing 3.5 (2.6)Spline screw IS-DG5x24 Buffer/front handle 3.5 (2.6)Spline screw IS-DG5x24 Buffer/engine housing 3.5 (2.6)Spline screw IS-DG5x24 Ignition module/engine housing 4.8 (3.5)Spline screw IS-DG6x52 Engine housing/cylinder 11.0 (8.1)

M12x1L Carrier (clutch) 50.0 (37.0)Collar stud DG8x24 Guide bar 16.0 (11.8)Collar stud M10x21 Guide bar/engine pan 30.0 (22.0) 1)

M14x1.25 Spark plug 25.0 (18.5)Hexagon nut M5 Muffler 9.0 (6.6)Hexagon nut M5 Box filter/carburetor 2.0 (1.5)Hexagon nut M5 Carburetor with box filter 3.2 (2.4)Hexagon nut M8x1 Flywheel 27.5 (20.3)

Use the following procedure to fit a DG screw in an existing thread:- Place the DG 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.

Remarks:

1) Screw must be secured with adhesive 0786 110 0126 (Loctite 649).

Note: Screws secured with adhesive are easier to release if the adhesive is heated first with a hot air blower (hairdryer). Exercise caution on polymer components.

STIHL 029, 039 7

Condition Cause Remedy

Saw chain turns at idle speed Engine idle speed too high Readjust at idle speedadjusting screw(counterclockwise)

Spring hooks broken Fit new springs

Loud noises Clutch springs stretched or Replace all clutch springsfatigued

Needle cage damaged Fit new needle cage

Clutch shoe retainer broken Fit new retainer

Clutch shoes and carrier Fit new clutchworn

Chain sprocket wears Chain not properly Tension chain as specifiedrapidly tensioned

Chain wears rapidly Chain not properly Tension chain as specifiedtensioned

Poor chain lubrication Check chain lubrication andrectify problem

Worn chain sprocket Fit new sprocket

Chain does not stop Brake spring broken Fit new brake springimmediately when brake isactivated Brake band stretched or Fit new brake band

broken

2. TROUBLESHOOTINGCHARTS

2.1 Clutch,Chain Drive,Chain Brake andChain Tensioner

STIHL 029, 039 8

2.2 Engine

Always check and, if necessary, repair the following parts before looking for faults on the engine:

- Air filter- Fuel system- Carburetor- Ignition system

Condition Cause Remedy

Engine does not start easily, Oil seals between cylinder Replace oil sealsstalls at idle speed, but operates and engine pan damagednormally at full throttle

Manifold leaking Seal or replace manifold

Engine pan leaking Seal engine pan

Engine pan damaged (cracks) Replace engine pan

Engine does not deliver full Secondary air seepage through Mount manifold correctly orpower or runs erratically poorly mounted or faulty replace

manifold

Piston rings leaking or Fit new piston ringsbroken

Muffler carbonized Clean muffler (inletand exhaust), replace sparkarresting screen (if fitted)

Engine overheating Insufficient cylinder Thoroughly clean all coolingcooling. Air inlets in fan air openingshousing blocked or cooling finson cylinder very dirtyIntake air preheating being Move shutter toused at too high an outside summer positiontemperature

STIHL 029, 039 9

2.3 Ignition System

Warning: Exercise extreme caution while carrying out maintenance and repair work on the ignition system.The high voltages which occur can cause serious or fatal accidents!

Ignition system in order.Look for fault in fuel system andcarburetor.

yes

Replace ignition module. Does enginenow run after positive spark test?

Fit new flywheel.Is spark test positive?

Use ohmmeter to check ignition leadfor break. If break is detected, replaceignition lead. Does spark test nowproduce sparkover?

Does flywheel appear to bein good condition?

Fit new spark plug.Is air gap correct?

Adjust air gap (0.15 - 0.3 mm).Is spark test positive?

Insert screwdriver in place of spark plug in spark plugterminal and hold about 4 mm (1/8") away fromground. Sparkover?

Replace faulty ignition lead of short circuit wire.Repair contact spring or switch shaft.

Faulty insulation on ignitionlead or short circuit wire?Is connector sleeve touching short circuitcontact?

Clean spark plug and reset electrode gap.Does spark test produce powerful spark?

Press terminal firmly onto sparkplug and fit spring if necessary.

Spark plug terminal firmly seated on spark plug?

Remove spark plug.Is it in good condition?

no

no

nono

no

yes

no

noyes

yes no

no

no

no

yes

yes

STIHL 029, 039 10

Condition Cause Remedy

Starter rope broken Rope pulled out too vigorously as Fit new starter ropefar as stop or over edge - i.e.not vertically

Normal wear Fit new starter rope

Rewind spring broken Spring overtensioned - Fit new rewind springno reserve when rope is fullyextended

Very dirty or corroded Fit new rewind spring

Starter rope can be pulled out Guide peg on pawl or pawl Fit new pawlsalmost without resistance itself worn(crankshaft does not turn)

Spring clip fatigued Fit new spring clip

Starter rope is difficult to Starter mechanism is very Thoroughly clean completepull and rewinds very slowly dirty (dusty conditions) starter mechanism

Lubricating oil on rewind spring Apply a few drops of kerosinebecomes viscous at very low (paraffin) to spring, then pulloutside temperatures (spring rope carefully several timeswindings stick together) until normal action is

restored

2.4 Rewind Starter

STIHL 029, 039 11

Important: In the event of trouble with the chain lubrication system, always investigate the other possible sourcesof faults before disassembling the oil pump.

Condition Cause Remedy

Chain receives no oil Oil tank empty Fill up with oil

Oil inlet hole in guide bar Clean oil inlet holeis blocked

Intake hose or pickup body Wash intake hose and pickup(strainer) clogged or intake body (strainer) in white spirithose ruptured and blow out with compressed air;

replace if necessary

Valve in oil tank blocked Clean or replace valve

Teeth on pump piston and/or Fit new oil pump and/orworm worn new worm

Machine losing chain oil Bore in pump Fit new pump housinghousing worn

Oil pump delivers too Control screw and/or Fit new control screw and/orlittle oil control edge on pump piston pump piston

worn

Bore in pump housing Fit new pump housingworn

2.5 Chain Lubrication

STIHL 029, 039 12

Note: For machines with automatic choke see 11.6.2.

Condition Cause Remedy

Carburetor floods; Inlet needle not sealing. Remove and clean or replaceengine stalls Foreign matter in valve seat or inlet needle,

cone damaged clean fuel tank, pickup body andfuel line if necessary

Inlet control lever sticking on Free off inlet control leverspindleHelical spring not located on Remove inlet control levernipple of inlet control lever and refit correctlyPerforated disc on diaphragm Fit new metering diaphragmis deformed and presses constantlyagainst inlet control leverInlet control lever too high Set inlet control lever flush(relative to design position) with bottom of metering chamber

Poor acceleration Idle jet "too lean" Back off low speed adjustingscrew slightly(see Carburetor Adjustment)

Main jet "too lean" Back off high speed adjustingscrew slightly(see Carburetor Adjustment)

Inlet control lever too low Set inlet control lever flush(relative to design position) with bottom of metering chamberInlet needle sticking to valve Remove inlet needle, cleanseat and refitConnecting bore to atmosphere Clean boreblockedDiaphragm gasket leaking Fit new diaphragm gasketMetering diaphragm damaged Fit new metering diaphragmor shrunk

Engine will not idle, Throttle shutter opened too wide Reset idle speed adjusting screwidle speed too high by idle speed adjusting screw correctly

2.6 Fuel System

STIHL 029, 039 13

Condition Cause Remedy

Engine stalls at idle speed Idle jet bores or ports Clean jet bores and portsblocked with compressed air

Idle jet "too rich" Screw down low speed adjustingscrew slightly(see Carburetor Adjustment)

Setting of idle speed Set idle speed adjustingadjusting screw incorrect screw correctly- throttle shutter completelyclosed

Small plastic plate in valve Clean or renew valve jetjet does not close

Engine speed drops quickly under Air filter plugged Clean air filterload - low power

Tank vent faulty Clean or replace tank ventif necessary

Leak in fuel line between tank Seal or renew connectionsand fuel pump and fuel line

Pump diaphragm damaged or Fit new pump diaphragmfatigued

Main jet bores or ports Clean bores and portsblocked

Fuel pickup body dirty Clean pickup body, fit newfilter

Fuel strainers dirty Clean fuel strainers

See also 2.2

STIHL 029, 039 14

3. CLUTCH, CHAIN DRIVECHAIN BRAKE ANDCHAIN TENSIONER

3.1 Clutch Drum andChain Sprocket

Top:Removing needle cage

Bottom:Assembly sequence of chain drive1 = Spur sprocket

Top: Top: 2 = Needle cageSprocket cover mounting nuts Removing E-clip 3 = Washer

4 = E-clipBottom: Bottom: 5 = Clutch drum (for rim sprocket)Disengaging chain brake Removing chain sprocket 6 = Rim sprocket

- Unscrew sprocket cover nuts - Remove the washer from the Note: Clean stub of crankshaft.and remove the sprocket cover. clutch drum or chain sprocket. Replace the needle cage or wash

it in clean white spirit and lubricate- Disengage the chain brake by - Remove the spur sprocket or rim with STIHL multipurpose grease,

pulling the hand guard back sprocket with clutch drum. see 12.2.toward the front handle.

- Take the needle cage out of the Push clutch drum/chain sprocket- Pry the E-clip off the crankshaft. clutch drum or chain sprocket. onto crankshaft and rotate it until

tang of spring on oil pump wormReassemble in the reverse engages the notch in the clutchsequence. drum.

Important: Rim sprocket must befitted with the chip ejector cavitiesfacing outward.

STIHL 029, 039 15

3.2 Clutch

Top:Removing prefilter Top: Top:

Locking strip 0000 893 5902 Unscrewing the clutchBottom:1 = Spark plug terminal Bottom: Bottom:2 = Spark plug Locking strip in position Assembly hook 5910 890 2800

Removing and disassembling - Push the locking strip into the - Remove the clutch drum or chainclutch: spark plug hole so that "TOP" or sprocket, see 3.1.

"OBEN" is facing upward.Troubleshooting chart - see 2.1. - Unscrew the clutch from the

Important: To avoid the risk of stub of the crankshaft.- Remove air filter - see 11.1. piston damage, use only the

specified locking strip. Caution: Clutch has a left-hand- Pull the prefilter out of the handle thread.

housing.

- Pull terminal off the spark plug.Unscrew the spark plug.

STIHL 029, 039 16

Top:Fitting retainer on

Top: clutch shoe Top:Removing a clutch spring Clutch clamped in a vise

Bottom:Bottom: Pushing clutch shoe Bottom:Component parts of clutch onto carrier Attaching clutch springs

- Use assembly hook to remove all Assembling and installing - Clamp the clutch, e.g. one shoe,the clutch springs. the clutch: in a vise.

- Pull the clutch shoes off the - Slip the retainers onto the clutch - Attach one end of each spring tocarrier. shoes so that the narrow side is the clutch shoes by hand.

next to the series number, e.g.- Pull the retainers off the clutch 1127. - Use the assembly hook to attach

shoes. the other ends of the springs and- Fit the clutch shoes over the press them firmly into the clutch

- Clean all parts and stub of arms of the clutch carrier so that shoes with one finger.crankshaft in white spirit. the series number, e.g. 1127, isReplace any damaged or worn on the same side as the carrier'sparts. hexagon.

STIHL 029, 039 17

Top: Top: Top:Tightening the clutch Bumper strip Detaching brake spring

Bottom: Bottom: Bottom:Fitting the prefilter Cover mounting screws Removing the brake band

- Screw clutch onto crankshaft - Remove the clutch drum or spur - Carefully remove the brakeand torque down to 50 Nm sprocket - see 3.1. spring from the anchor pin.(37 Ibf.ft).

- Engage the chain brake. - Ease the brake band out of its- Install clutch drum or spur seat in the engine housing.

sprocket - see 3.1 - Remove the upper bumper stripfrom its seat.

- Remove locking strip fromcylinder. Install spark plug - Remove mounting screws fromand torque down to 25 Nm cover and lift cover away.(18.5 Ibf.ft).

- Install the air filter - see 11.1.

- Fit the prefilter so that its tabsengage the recesses in thehandle housing.

3.3 Chain Brake

3.3.1 Disassembly

STIHL 029, 039 18

Top:Removing the Top:brake band Top: Washer on pivot pin

E-clip on bell crank pivot pinBottom: Bottom:Hand guard mounting Bottom: 1 = Hand guardscrew Removing the link (strap) 2 = Bell crank

- Remove the brake band from the - Pry the E-clip off the bell crank - Remove washer from bell crankretaining lug and disconnect it pivot pin. pivot pin.from the bell crank.

- Remove the link (strap) from the - Carefully pull the hand guard and- Take out the hand guard moun- bell crank pivot pin. bell crank off their pivot pins and

ting screw. lift them away together.- Slide the link up and take it off

the hand guard pivot pin.

STIHL 029, 039 19

3.3.2 Assembly

Top:1 = Spring Top:2 = Cam lever Pressing cam lever3 = E-clip downward

Bottom: Bottom:Fitting bell crank in Correct installed position

Disconnecting the spring hand guard of hand guard

- Remove the E-clip from the camlever pivot pin.

- Disconnect spring from the camlever. Pull the cam lever off thepivot pin.

- Remove the spring.

- Clean all disassembled parts inwhite spirit. Replace any worn ordamaged parts.

- Push the cam lever onto the pivot - Position bearing boss of handpin and secure it with the E-clip. guard against the pivot pin and fit

the other side of the hand guard- Attach the spring to the cam over the handle housing.

lever, from behind, and push itover the pivot pin. - Press the cam lever downward

and push the hand guard and- Insert the bell crank in the side of bell crank onto the pivot pins.

the hand guard so that the shortarm of the bell crank points up.

STIHL 029, 039 20

Top: Top:Fitting the link Top: Assembly tube 1117 890 0900

Fitting the brake bandBottom: Bottom:Attaching brake band to bell Bottom: Attaching brake spring tocrank Attaching the brake spring anchor pin

- Fit the washer on the bell crank Important: Coat sliding and - Slip the bush over the handpivot pin. bearing points with Molykote guard mounting screw. Fit screw

grease - see 12.2. Do not and tighten to 3.5 Nm (2.6 Ibf.ft).- Position the link on the hand lubricate the brake band.

guard pivot pin and slide it down - Fit cover for brake band.until it engages the groove on the - Attach the brake spring to theend of the pivot pin. Then push bell crank. - Fit bumper strip in its seat.link over the bell crank pivot pinand secure it with the E-clip. - Use the assembly tool and a - Install the clutch drum or chain

screwdriver to attach the brake sprocket - see 3.1.- First attach brake band to bell spring to the anchor pin.

crank and then push it into theengine housing recess.

STIHL 029, 039 21

3.4 Front ChainTensioner

3.5 Side ChainTensioner

Top:1 = Adjusting screw Top:2 = Adjusting nut Cover mounting screw

a = 19.5 mm (0.77")Bottom: b = 1.7 mm (0.07") Bottom:Removing cover c = 10 mm (0.4") Removing the chain tensioner

Note: The front chain tensioner canbe converted to a side chaintensioner - see 3.5.

In the case of a coversion fromfront to side chain tensioner, it isnecessary to drill a hole in thesprocket cover to take the peg of thespur gear - see dimensions inillustration.

Reverse the above sequence toinstall the chain tensioner.

- Remove the chain sprocket cover.

- Take out the cover mountingscrew.

- Pull the chain tensioner assem-bly out of the engine housing.

- Remove chain sprocket cover.

- Unscrew the adjusting nut byrotating the adjusting screw.

- Take the adjusting screw out ofthe cover and housing.

- Pull the cover out of the enginehousing.

STIHL 029, 039 22

3.6 Bar MountingStuds

Top:1 = Thrust pad2 = Tensioner slide3 = Adjusting screw4 = Spur gear5 = Cover

Bottom: Removing tensioner slide Unscrewing collar stud withWithdrawing the spur gear and adjusting screw stud puller 5910 893 0501

- Pull the tensioner slide off the - Remove the sprocket cover.cover.

- Push the stud puller over the- Take the adjusting screw out of front collar stud (next to spiked

the cover. bumper) as far as it will go. Usea 15 mm wrench to unscrew the

- Inspect the teeth on the spur collar stud counterclockwise.gear and adjusting screw. If theteeth are damaged, replace both - Fit the collar stud and torque itparts. down to 16 Nm (11.8 Ibf.ft).

Note: The collar stud next to theReverse the above sequence to chain sprocket is installed withinstall the chain tensioner. Loctite.

Note: Coat teeth of adjusting - Remove the muffler - see 4.1.screw and spur gear with grease,see 12.2, before refitting. - Use hot air blower (e.g. hair

dryer) to heat engine pan aroundthe collar stud. Then unscrew thecollar stud with the stud puller.

- Coat thread of collar stud withLoctite, see 12.2.

- Fit collar stud and torque it downto 30 Nm (22 Ibf.ft).

- Install the muffler - see 4.1.

- Take the thrust pad off theadjusting screw.

- Rotate spur gear until theadjusting screw comes is clearof the tensioner slide.

- Pull the spur gear out of thecover.

STIHL 029, 039 23

- Remove the gasket.

- Take the mounting screws out oftheir seats on the cylinder.

Reassemble in the reversesequence.

Note: Install a new gasket. Use newflanged locknuts and tighten themdown to 8.5 Nm (6.2 Ibf.ft).

These machines do not have aconventional crankcase - the engineconsists of the cylinder, piston,crankshaft and engine pan.

Troubleshooting chart - see 2.2.

- Unscrew flanged locknuts frommuffler.

- Remove muffler together with cover.

4. ENGINE

4.1 Removing and RefittingExhaust Muffler

- Remove the cover from themuffler.

- Remove the spark arrestingscreen, if fitted, from the muffler.

- Clean the spark arresting screen orfit a new one if necessary.

Top:Gasket

Bottom:Removing the screws

Top:Removing the cover

Bottom:Removing the spark arresting screen

Top:Flanged locknuts on muffler

Bottom:Removing the muffler

STIHL 029, 039 24

4.2.1 Preparations

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

The engine housing can be checkedaccurately for leaks with thecarburetor and crankcase tester andthe vacuum pump.

- Remove the muffler - see 4.1.

- Position the sealing platebetween the mounting screws.

Top:1 = Sealing plate 0000 855 81062 = Flange 1123 855 42003 = Sleeves 1127 851 8300

Bottom:Sealing plate betweenmounting screws

4.2 Leakage Testingthe Engine

Top:Carburetor and crankcase tester1106 850 2905

Bottom:Vacuum pump 0000 850 3500

Defective oil seals and gaskets orcracks in castings are the usualcauses of leaks. Such faults allowsupplementary air to enter theengine and thus upset the fuel-airmixture.

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

STIHL 029, 039 25

4.2.2 Pressure Test

- Check to see that the pin in thetest flange is in bore No. 1 andfit it if necessary.

- Fit the test flange in place of thecarburetor.

Important: When fitting the testflange, make sure the pin isproperly located in the impulsehose.

- Fit the flange in place of themuffler.

- Push the sleeves over the mountingscrews. Fit the nuts and tightenthem firmly.

Note: Sealing plate must completelyfill the space between the twomounting screws.

- Remove carburetor - see 11.2.

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

- Connect tester's pressure hoseto nipple on test flange.

- Make sure the spark plug isproperly tightened down beforestarting the test.

- Close the vent screw on therubber bulb.

- Use rubber bulb to pump air intothe engine housing until the gaugeshows a pressure of 0.4 bar(5.8 psi). If this pressure remainsconstant for at least 20 seconds,the engine housing is airtight.

Top:Flange 1123 855 4200 fitted in position

Bottom:Test flange 1128 850 4200

Top:1 = Bore No. 12 = Bore No. 2

Bottom:Test flange fitted in position(pin in impulse hose)

Top:Tester's pressure hose fitted on test flange nipple

Bottom:Closing the vent screw

STIHL 029, 039 26

4.2.3 Vacuum Test

Tester's suction hose connectedto nipple on test flangePressure-testing the engine

- Remove the test flange and refitthe carburetor - see 11.2.

- Remove the flange and sealingplate.

- Refit the muffler - see 4.1.

However, if the indicated pressuredrops, the leak must be located andthe faulty part replaced. Note: Coatthe suspect area with oil andpressurize the engine housingagain. Bubbles will appear if there isa leak in the oiled area.

- Carry out the vacuum test - see4.2.3.

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

Oil seals tend to fail when subjectedto a vacuum, i.e. the sealing lip liftsaway from the crankshaft during thepiston's induction stroke becausethere is no internal counterpressure.

An additional test can be carried outwith the vacuum pump to detect thiskind of fault. The preparations for thistest are the same as for the pressuretest - see 4.2.1.

- Connect the vacuum pump's suctionhose to test flange nipple.

- Pull out the pump piston severaltimes until the gauge indicates avacuum of 0.4 bar (5.8 psi).

STIHL 029, 039 27

Note: When you release the pumppiston, the non-return valve auto-matically seals the suction hose. If thevacuum reading remains constant, orrises to no more than 0.3 bar(4.25 psi) within 20 seconds, it can beassumed that the oil seals are in goodcondition.

However, if the pressure continues torise (reduced vacuum in crankcase),the oil seals must be replaced, even ifno leaks were

detected in the pressure test.

- Remove the test flange and refitthe carburetor - see 11.2.

- Remove the flange and sealingplate.

- Refit the muffler - see 4.1.

Note: If oil seals have to bereplaced - see 4.3.

4.3 Replacing theOil Seals

Leakage test with vacuum pump

Top:Puller 0000 890 4400 withNo. 6 jaws 0000 893 3711

Bottom:Removing oil seal atclutch side

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

Clutch side:

- Remove the oil pump - see 10.3.

- Apply the puller and withdraw theoil seal at the clutch side.

STIHL 029, 039 28

Installing oil seal withoutpress sleeve

- Wait about one minute and thenrotate the crankshaft severaltimes.

- Remove the assembly sleeve.

- Install the oil pump - see 10.3.

Ignition side:

- Remove the flywheel - see 5.1.5.

- Apply the puller and withdraw the oilseal at the ignition side.

Note: Take care not to damage thecrankshaft in the area of the oil seal.If new oil seals have already beeninstalled, use sealing ring puller andNo. 3.1 jaws to pull out the clampingring. Pry the remaining part of the oilseal out of the housing.

- Clean the sealing surface with asolvent-based degreasantcontaining no CFCs.

- Pack space between sealing anddust lips with grease - see 12.2.

- Apply thin coating of sealant, see12.2, to outside diameter of the oilseal.

- Slip the assembly sleeve 1122893 4600 over the end of thecrankshaft.

- Position oil seal so that theclamping ring points up. Use thepress sleeve to press home the oil seal as far as stop.

Note: Remove oil seal withclamping ring as described forclutch side.

- Clean the sealing surface with asolvent-based degreasantcontaining no CFCs, and apply thincoating of sealant, see 12.2, tooutside diameter of oil seal.

- Pack space between sealing anddust lips with grease - see 12.2.

- Position the oil seal so that theclamping ring points up. Use thepress sleeve to to press home theoil seal as far as stop.

Note: If the press sleeve is notavailable, the oil seals can bepressed into the housing by hand.

- Wait about one minute and thenrotate the crankshaft several times.

- Fit the flywheel - see 5.1.5.

Top:Installing oil seal with press sleeve1127 893 2400

Bottom:Removing oil seal atignition side

Replacement oil seal1 = Sealing lip2 = Clamping ring3 = Dust lip

STIHL 029, 039 29

4.4 Removing and Installingthe Engine

Always check and, if necessary, repairthe fuel system, carburetor, air filterand ignition system before looking forfaults on the engine.

- Remove handle housing see8.1.1.

- Remove the flywheel - see 5.1.5.

- Remove the oil pump - see 10.3.

- Remove the muffler - see 4.1.

- Pull the terminal off the spark plugand unscrew the spark plug.

- Remove the ignition lead fromthe retainer and groove on thecover.

- Take out the cover mountingscrews and lift the cover away.

- Remove the ground wirefastening screw from thecylinder.

- Remove the collar stud next tothe brake band.

Important: The collar stud is installedwith Loctite. Use hot air blower (e.g.hair dryer) to heat engine pan aroundthe collar stud.

- Remove the engine pan mountingscrews from the cylinder.

Top:Cover mountingscrews

Bottom:Ground wirefastening screw

1 = Spark plug terminal2 = Spark plug3 = Ignition lead retainer

Top:Bar mountingstud

Bottom:Engine housing/enginemounting screws

STIHL 029, 039 30

4.5 Cylinder

Top:Impulse hose

Bottom:1 = Hose clamp2 = Manifold

Correct position of ignition leadin cover1 = Tank vent

Top:Removing the engine

Bottom:Sequence for tightening screws

- Fit mounting screw 1 as far asstop.

- Coat thread of collar stud 4 withLoctite - see 12.2.

- Fit collar stud 4 and torque itdown to 30 Nm (22 Ibf.ft).

- Fit mounting screws 2, 3 and 5and torque them down to 11 Nm(8 Ibf.ft).

- Tighten down mounting screw 1 to11 Nm (8 Ibf.ft).

- Push ignition lead into grooveand retainer on cover.

- Push the tank vent into the hole inthe cover.

- Remove the engine - see 4.4.

- Pull the impulse hose off thenipple on the cylinder.

- Release the hose clamp on themanifold. Pull the manifold off theintake port.

- Lift the engine sideways out ofthe engine housing.

To replace engine housing - see11.9.

Assembly is a reversal of thedisassembly sequence.

Note: Pay special attention to thefollowing points.

STIHL 029, 039 31

- Pull the engine pan off thecylinder.

- Lift the crankshaft and pull thepiston out of the cylinder.

- Inspect the cylinder and replaceit if necessary.

Note: If a new cylinder has to beinstalled, always fit the matchingpiston. Replacement cylinders areonly supplied complete with pistonfor this reason.

- Thoroughly clean all residue ofsealant from the cylinder andengine pan mating faces.

- Lubricate piston and piston ringswith oil.

- Position the piston rings so thatthe radii at the ring gap meet atthe fixing pin in the piston groovewhen the rings are compressed.

Note: The clamping strap can onlybe used with cylinders whose innercontour is the same as that shown inthe illustration above.

- Use the clamping strap to com-press the piston rings around thepiston and check that the pistonrings are correctly positioned.

- Close the clamping strap andcompress it so that the lug engagesthe square hole.

- Position the clamping strap so thatits channel sections line up with thecenter of the piston pin.

Top:Inner contour of cylinder

Bottom:Clamping strap 1127 893 2600

Correct position ofpiston rings

Top:Fitting clamping strap onpiston rings

Bottom:1 = Piston pin2 = Channel section onclamping strap

STIHL 029, 039 32

Top:Fitting the piston

Bottom:1 = Long crankshaft stub2 = Exhaust port

Top:Straight faces on manifold andintake port

Bottom:Correct position of hose clampa = 8 mm (5/16")

- Fit the hose clamp on the manifoldso that its ends point up and thescrew head is on the left.

- Tighten the screw until the gapbetween the two ends of the hoseclamp is about 8 mm (5/16").

- Assembly of all other parts is now areversal of the disassemblysequence.

- Apply a thin coating of sealant tothe outer diameters of the oil seals- see 12.2.

- Position piston with clamping strapin cylinder so that the channelsections on the clamping strap reston the lands in the cylinder.

- Carefully push the piston into thecylinder. Open the clamping andtake it away.

- Line up the crankshaft so that itslong stub is on the right - looking atthe exhaust port.

- Apply a thin bead of sealant to theengine pan mating face - see 12.2.

Note: Follow manufacturer'sinstructions for use of sealant.

- Fit the engine pan so that the seatfor the oil pump is at the same sideas the long crankshaft stub.

- Push the manifold on to the intake port so that the straight facesof the manifold and intake port are inalignment.

1 = Long crankshaft stub2 = Tapped hole for bar

mounting stud

STIHL 029, 039 33

4.6 Piston

- Pull the piston out of the cylinder -see 4.5.

- Use a scriber or similar tool toease the hookless snap ringsout of the grooves in the pistonbosses.

- Use the assembly drift to pushthe piston pin out of the piston. Ifthe piston pin is stuck, tap theend of the drift lightly with ahammer if necessary.

head is marked with the letter "N", asin the inside of the piston.

- Lubricate the needle cage with oiland fit it in the small end.

- Fit a snap ring in one piston boss.

Note: Use special installing tool5910 890 2210 to fit the snap ring.

Top:Needle cage in small end

Bottom:1 = Installing tool 5910 890 22102 = Sleeve

Top:Pushing out piston pin

Bottom:Piston rings1 = "N" marking on piston

head

Top:Removing snap ring

Bottom:Assembly drift 1110 893 4700

Important: Hold the piston steadyduring this process to ensure that nojolts are transmitted to the con-necting rod. Remove the piston andtake the needle cage out of theconnecting rod.

- Inspect piston rings and replace ifnecessary - see 4.7.

Note: Only special pistons may beinstalled in low compressions saws(i.e. "N"). The machine numbers oflow compression saws have the suffix"N". In addition, the piston

STIHL 029, 039 34

Top:1 = Flat on end of shank2 = Pin

Bottom:Pushing installing tool into sleeve as faras stop

- Remove the sleeve and slip itonto the other end of the shank.

Note: Pin must point toward flatface of tool's shank.

- Apply the installing tool to thepiston boss, hold the pistonsteady, center the tool shankexactly and press home until thesnap ring slips into the groove.

- Push the slotted diameter of thesleeve over the magnet and snapring so that the inner pin points at the flat face of the tool's shank.

- Stand the installing tool, sleevedownward, on a flat surface(wooden board) and pressvertically downwards until thesleeve butts against the tool'sshoulder.

Owing to the special shape of thepiston it is necessary to modify thesleeve of the installing tool as shownin the illustration.

Use the installing tool as follows:

- Remove the sleeve from the tool.

- Attach the hookless snap ring to themagnet so that the snap ring gap ison the flat side of the tool's shank(see illustration).

Top:Modified sleevea = 16 mm (11/16")b = 8 mm (5/16")c = 20 mm (25/32")

Bottom1 = Snap ring (hookless)2 = Magnet

Top:Slipping sleeve onto other end ofshank

Bottom:Fitting snap ring inpiston boss

STIHL 029, 039 35

4.7 Piston Rings

Note: The snap ring must be fitted sothat the ring gap is on the piston'svertical axis (it must point either up ordown).

- Heat the piston on an electricheating plate to approx. 60C(140F) and slip it over the con-necting rod so that the mark (arrow)on the piston head points towardsyou - the long stub of the crankshaftmust be on the left.

- Push the assembly drift, smalldiameter first, through the snap ringalready fitted, the piston bore andthe small end (needle cage). Line upthe piston.

- Fit the piston pin on the assemblydrift and slide it into the piston (thepiston pin slides home easily whenthe piston is hot).

- Use the installing tool 5910 8902210 to fit the snap ring in thepiston boss.

Note: The snap ring must be fittedso that the ring gap is on thepiston's vertical axis (it must pointeither up or down).

- Install the piston - see 4.5.

- Remove the piston fromthe cylinder - see 4.5.

- Remove rings from piston.

- Use a piece of an old pistonring to scrape the groovesclean.

- Install the new piston rings inthe grooves so that the radii atthe ring gaps face upward.

- Install the piston - see 4.5.

Top:Piston ring grooves

Bottom:Fitting piston ring

Top:Installing the piston pin

Bottom:Insetting snap ring with installingtool 5910 890 2210

1 = Mark (arrow)2 = Long crankshaft stub

STIHL 029, 039 36

4.8 Crankshaft

Top:1 = Crankshaft2 = Connecting rod

Bottom:Oil seals

Top:Ball bearings

Bottom:Closed side of ball bearing

1 = Sealing lip2 = Clamping ring

- Pack space between sealing anddust lips of oil seals with grease -see 12.2.

- Apply thin coating of sealant, -see 12.2, to outside diameters of oilseals.

- Slide oil seals on to crankshaftstubs so that the clamping ringpoints outward (sealing lip alsopoints outward).

Assembly of other parts is areversal of the disassemblysequence.

- Remove the piston - see 4.6.

- Pull both oil seals off the crank-shaft stubs.

- Pull both ball bearings off thecrankshaft stubs.

- Note that closed side of ballbearings must face outwardwhen they are installed. Heatnew ball bearings to approx.50C (120F) and push them onto the crankshaft stubs as far asstop.

The crankshaft, connecting rod andneedle bearing are an inseparableassembly. This means that thecrankshaft must always be replacedas a complete unit in the event ofdamage to any one of these parts.

When fitting a replacement crank-shaft, always install new ballbearings and oil seals.

STIHL 029, 039 37

5.1 Repairing ComponentParts

5.1.1 Spark Plug

5. IGNITION SYSTEM

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

STIHL 029 and 039 chain saws areequipped with an electronic(breakerless) magneto ignitionsystem which requires no outsidepower source (battery or dynamo).

The system basically consists of anignition module and flywheel and iseasily accessible.

- Check the electrode gap atregular intervals with a feelergauge. It should be 0.5 mm(0.02").

- Bend the ground electrode asnecessary.

Important: Always fit a new sparkplug if the electrodes are badlyeroded.

Troubleshooting on the ignitionsystem should always begin at thespark plug.

In the event of starting difficulties, lowengine power, misfiring, etc., unscrewthe spark plug and check that it is theapproved type. Only the spark plugslisted in the specifications may beused. Other makes of spark plug areunsuitable because they have long-reach electrodes.

Sooted or carbonized spark plug:

- Use brass wire brush to clean thespark plug and then blow it clearwith compressed air.

Note: Never use a steel wirebrush for this job.

Spark plug smeared with oil:

- Wash the insulator nose with agrease solvent and blow it clearwith compressed air.

Electrode gap:

Electrode gap becomes wider as aresult of normal erosion.

Top:Checking electrode gap withfeeler gauge

Bottom:Resetting electrode gap withBosch spark plug gauge

1 = Ignition module2 = Flywheel

STIHL 029, 039 38

Checking the spark plug:

Accurate checking of the spark plugis only possible with a special sparkplug tester.

A provisional check can be carriedout by fitting a clean spark plug in thespark plug terminal and holding itagainst ground. Set the MasterControl to the "RUN" position. Thereshould be a powerful sparkover at theelectrodes when you crank theengine with the starter rope.

Warning: Do not touch any liveparts - contact with high voltagecan cause serious or fatalaccidents.

Note: It is recommended that anew spark plug be fitted in allcases of doubt.

If there is no sparkover eventhough the spark plug is in goodcondition, first check the con-nections.

Note: Chafed insulation on the ignitionlead or short circuit wire will cause ashort-circuit to ground. In this case theengine with either not start or only runerratically.

Installing the spark plug:

- Clean the spark plug seat andinspect the sealing ring to makesure it is in good condition.

- Fit the spark plug and tighten it to25 Nm (18.5 Ibf.ft).

The appearance of the spark plug's insulator nose gives valuable information with regard to the effects of variousoperating conditions:

Grayish yellow to brown, dry

Velvet-like, dull black coating ofsoot

Coating of damp oil carbon andsoot

Welding beads on insulator nose,pitted electrodes

Condition of insulator nose

Normal:

Sooted:

Smeared with oil:

Overheated:

Meaning

Engine in order; correct spark plug(heat range as specified)

Mixture too rich, lack of air (dirty airfilter, choke shutter partly closed),electrode gap too wide, wrong sparkplug (heat range too high)

Too much oil in fuel mix

Mixture too lean, spark plug loose,wrong spark plug (heat range toolow)

STIHL 029, 039 39

5.1.2 Ignition Module 5.1.2.1 Ignition Timing 5.1.2.2 Removing and Installing

Top:1 = Spark plug terminal2 = Ignition lead retainer3 = Groove

Bottom:1 = Lead retainer2 = Short circuit wire

1 = High voltage output2 = Connector tag

The ignition module accommodatesall the components required to controlignition timing. There are twoelectrical connections on the coilbody:

1. the high voltage output2. the connector tags for the short

circuit wires

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 must beinstalled if no ignition spark isobtained (after checking that wiringand stop switch are in goodcondition).

- Remove handle housing - see8.1.1.

- Pull terminal off the spark plug.

- Remove the ignition lead fromthe retainer and groove on thecover.

- Pull the short circuit wire off thetag on the ignition module andremove it from the lead retainer.

Ignition timing on the electronic(breakerless) magneto ignitionsystem is fixed at 2.4 mm (0.095")B.T.D.C. at 8,000 r.p.m. and is notadjustable.

However, in view of the permis-sible tolerances in the electroniccircuit, it may vary between 2.0and 2.8 mm (0.080" and 0.11 ")B.T.D.C. at 8,000 r.p.m.

Since there is no mechanical wear inthese systems, ignition timing cannotget out of adjustment. However, aninternal fault in the circuit can alter theswitching point in such a way that aspark test will still show the system tobe in order although timing is outsidethe permissible tolerance. This willimpair engine starting and runningbehavior.

STIHL 029, 039 40

Remove the ignition modulemounting screws.

Pull the ignition module forwardand push back the grommet onthe high voltage output.

Unscrew the ignition lead from thecontact pin and pull it out of theignition module.

If necessary, ease the peg of thelead retainer out of its seat andremove the retainer.

Note: Before fitting the ignition lead,pack the high voltage output withSTIHL multipurpose grease see 12.2.

Important: Do not use graphitegrease (Molykote) or siliconeinsulating paste for this job.

- Push the grommet over theignition module's high voltageoutput.

- Place the ignition module inposition, fit screws but do nottighten down yet.

Important: Secure ground wire withupper screw and fit a washer on thelower screw.

- Slide the setting gauge betweenthe arms of the ignition module andthe flywheel magnets.

- Press the ignition module againstthe flywheel and tighten down themounting screws to a torque of4.8 Nm (3.5 Ibf.ft).

Important: Tighten the upperscrew first.

- Remove the setting gauge anduse a feeler gauge to check the airgap. It should be 0.15 - 0.3 mm(0.006 - 0.012").

Assembly of the remaining parts isnow a reversal of the disassemblysequence.

Setting gauge fitted betweenflywheel and ignition module

Top:Removing lead retainer

Bottom:Setting gauge 1127 890 6400

Top:Ignition module mountingscrews

Bottom:Pulling the unscrewed ignition leadout of ignition module

STIHL 029, 039 41

5.1.3 Spark Plug Terminal

Top:Removing dust seal

Bottom:Pulling leg spring out of sparkplug terminal

- Fit the dust seal over the sparkplug terminal.

- Fit the terminal on the spark plug.Push the ignition lead into theretainer and groove on the cover.

- Fit the handle housing - see 8.1.1.

- Remove handle housing - see8.1.1.

- Pull terminal off the spark plug andremove the ignition lead from theretainer.

- Pull the dust seal off the sparkplug terminal and push it downthe ignition lead.

- Use a suitable pair of pliers togrip the leg spring and pull it outof the spark plug terminal.

- Unhook the leg spring from theignition lead and slip the sparkplug terminal and dust seal offthe lead.

- Slip the dust seal over theignition lead.

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

- Fit spark plug terminal over theignition lead.

- Use suitable pliers to grip the end ofthe ignition lead inside the sparkplug terminal and pull it out.

Pinch the hook of the leg spring intothe center of the lead, i.e. about 10mm (3/8") from the end of the lead.

- Pull the lead back into theterminal so that the leg springlocates properly inside it (seeillustration).

Fitting dust seal

Top:Fitting the leg spring

Bottom:Correct position of leg spring in sparkplug terminal

STIHL 029, 039 42

- Remove ignition module - see5.1.2.2.

- Pull the grommet off the ignitionlead.

- Pull the ignition lead out of thehole in the tank housing.

- Remove the spark plug terminal -see 5.1.3.

Removing the flywheel:

- Block piston with locking strip -see 3.2.

- Take out the fan housing mount-ing screws and remove the fanhousing.

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

Reassembly is a reversal of thedisassembly sequence.

Note: Use a pointed tool (awl orgimlet) to pierce the center of theother end of the ignition lead whichscrews into the module.

Note: Before fitting the ignition lead,pack the high voltage output withSTIHL multipurpose grease see 12.2.

Important: Do not use graphitegrease (Molykote) or siliconeinsulating paste for this job.

5.1.5 Flywheel5.1.4 Ignition Lead

Top:Grommet

Bottom:Pulling ignition lead out oftank housing Piercing center of ignition lead

Top:Locking strip 0000 893 5902 incylinder

Bottom:Fan housing mountingscrews

STIHL 029, 039 43

Top:Puller 1116 893 0800

Bottom:Puller fitted in position

1 = Flywheel2 = Magnet poles

- Inspect the condition of theflywheel. If you find any damage(e.g. cracks, broken fan blades),fit a new flywheel.

Installing the flywheel:

Important: Clean the stub of thecrankshaft and the flywheel hubbore with a standard commercial,solvent-based degreasant containingno CFCs. Fit the flywheel and tightenmounting nut to 27.5 Nm (20 Ibf.ft).

Assembly of the remaining parts isnow a reversal of the disassemblysequence.

Note: If the flywheel cannot beremoved by hand, screw the pulleronto the crankshaft stub, tap the endof the puller lightly with a hammer torelease the flywheel. Unscrew thepuller.

- Rotate the flywheel so that themagnet poles are opposite theignition module.

- Unscrew flywheel mounting nutfrom the crankshaft.

- Pull the flywheel off the crank-shaft.

Top:Flywheel mounting nut

Bottom:Removing the flywheel

STIHL 029, 039 44

5.1.6 Short Circuit Wire/Ground Wire

5.1.7 Contact Spring

- Remove handle housing - see8.1.1.

Remove the flywheel - see 5.1.5.

- Remove the ignition module-see 5.1.2.2.

- Remove the ground wirefastening screw from thecylinder.

- Remove the air filter - see 11.1.

- Remove the switch shaft - see9.1.

- Pull the ground wire terminal offthe contact spring.

- Ease the contact spring out of itsseat in the handle housing.

Installation is a reversal of theremoval sequence.

- Pull the short circuit and groundwires out of the hole in the enginehousing.

- Pull the grommet off the shortcircuit and ground wires.

Installation is a reversal of theremoval sequence.

Top:Ground wire fasteningscrew

Bottom:Withdrawing short circuit wire andground wire Grommet

Top:Ground wire terminal

Bottom:Removing contact spring

STIHL 029, 039 45

Top:Removing spring clip

Bottom:Pulling rope rotor off thestarter post.

Fan housing mountingscrews

6.2 Rope Rotor/Pawl

If the action of the starter ropebecomes very stiff and the roperewinds very slowly or not completely,it can be assumed that the startermechanism is in order but pluggedwith dirt. At very low outsidetemperatures the lubricating oil on therewind spring may thicken and causethe spring windings to stick together.This has a detrimental effect on thefunction of the starter mechanism. Insuch a case it is sufficient to apply afew drops of paraffin (kerosine) to therewind spring.

Carefully pull out the starter ropeseveral times and allow it to rewinduntil its normal smooth action isrestored.

If clogged with dirt or pitch, the entirestarter mechanism, including therewind spring, must be removed anddisassembled. Take special carewhen removing the spring.

Wash all parts in paraffin or whitespirit.

Lubricate the rewind spring andstarter post with STIHL speciallubricant, see 12.2, before instal-ling.

Removing rope rotor:

Troubleshooting chart - see 2.4.

The fan housing has to be re-moved for access to the startermechanism.

Relieving tension of rewindspring:

- Pull out the starter rope to alength of approx. 5 cm (2 - 3 in)and hold the rope rotor steady.

- Take two turns of the rope off therotor.

- Pull out the starter grip and let goof the rope rotor.

Note: The rope rotor will spin backand relieve the tension of the rewindspring. The rewind spring will not beunder tension if the starter rope isbroken.

- Remove the starter rope from therotor.

- Use screwdriver or suitable pliersto carefully remove the spring clipfrom the starter post.

- Take the washer and rope rotorand with pawl off the starter post.

- If necessary, remove the pawlfrom the rope rotor.

- Replace the worn or brokenstarter rope - see 6.3.

6. REWIND STARTER

6.1 RoutineMaintenance

STIHL 029, 039 46

6.3 Replacing theStarter Rope

Top:1 = Special knot2 = Rope guide bush

Bottom:Special knots used

1 = Spring clip2 = Pawl3 = Washer

- Remove the rope rotor - see 6.2.

- Remove the remaining rope fromthe rope rotor. Thread end of newrope (3.5 mm (0.14") dia., 960mm (37.8") long) through the rotorand secure it with a simpleoverhand knot.

- Pull the rope back into the rotorso that it locates in the recess.

- Thread the other end of the ropethrough the guide bush frominside the fan housing and throughthe bottom of the starter grip.Secure with one of the specialknots shown.

- Install the rope rotor - see 6.2.

Top:Correct position of starter rope inrope rotor

Bottom:Starter rope secured in rope rotor withknot

Installing the rope rotor:

- Lubricate guide peg on pawl withgraphite grease, see 12.2, and thenfit the pawl.

- Coat the bore in the rope rotor withSTIHL special lubricant - see 12.2.Fit the rotor on the starter post sothat the inner spring loop slides intothe lug on the rotor.

Note: Check that the spring loophas engaged by turning the roperotor slightly and letting it go - itmust spin back.

- Fit the washer and install thespring clip in the starter postgroove.

Note: Make sure the spring clipengages the pawl guide peg andpoints it in the clockwise direction.

- The spring clip must be treatedvery carefully. If it is bent ortwisted during disassembly orassembly, the rewind startermight malfunction.

- Tension the rewind spring see 6.5.

STIHL 029, 039 47

6.5 Tensioning theRewind Spring

6.4 Replacing theRewind Spring

- Remove the rope rotor, see 6.2.Take out the spring housing. Usepliers to remove any remainingpieces of spring from the fanhousing.

- The rewind spring is suppliedready for installation with thespring housing. It should belubricated with a few drops ofSTIHL special lubricant beforeinstallation.

- Position the rewind spring withspring housing (bottom plate mustface up) in the fan housing.Engage the anchor loop over thelug in the starter cover.

Caution: The rewind spring canpop out and uncoil during install-ation.

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

- Position anchor loop about 20mm (3/4") from the edge of thespring housing.

- Refit the rewind spring in thespring housing in the counter-clockwise direction, startingoutside and working inwards.

Note: The wooden assembly blockcan be placed over the springhousing to simplify refitting.

- Install the rope rotor - see 6.2.

- Make a loop in the starter rope.

- Grip the rope close to the rotorand use it to turn the rope rotorsix full turns clockwise.

- Hold the rope rotor steady.

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

Top:Position of anchor loop a =20 mm (3/4")

Bottom:Fitting rewind spring with aid of woodenassembly block 1108 893 4800

Top:Tensioning the rewind spring

Bottom:Straightening twisted ropeRewind spring in position

STIHL 029, 039 48

- Hold the starter grip firmly tokeep the rope tensioned.

- Let go of the rope rotor andslowly release the starter grip.

Note: The rewind spring is correctlytensioned when the starter grip sitsfirmly in the rope guide bush withoutdrooping to one side. If this is not thecase, tension the spring by oneadditional turn.

When the starter rope is fullyextended, it must still be possible torotate the rope rotor at least anotherhalf turn before maximum springtension is reached. If this is not thecase, pull the rope out, hold the roperotor steady and take off one turn ofthe rope.

Do not overtension the rewindspring as this will cause it tobreak.

- Refit the fan housing.

The wear on the guide bush isaccelerated by the starter rope beingpulled sideways. The wall of the guidebush eventually wears through,becomes loose and has to bereplaced.

- Remove the fan housing.

- Remove the rope rotor, see 6.2,take off the starter grip and pull outthe rope.

- Use a screwdriver to pry the oldbush out of the fan housing.

Installing the new rope bush:

- Place the new bush in its seat inthe fan housing.

- Insert the screw spindle of theinstalling tool through the bushfrom inside the housing.

- Fit the thrust sleeve, tapered endfirst, and the hexagon nut.

Rope guide bushGrip on fan housing

6.6 Replacing the StarterRope Guide Bush

Top:Installing tool 0000 890 2201

Bottom:Flaring the new ropeguide bush

- Tighten down the hexagon nutuntil the bush is firmly seated.

Note: The installing tool flares the lowerend of the rope bush.

- Refit the starter rope and starter grip.

- Install the rope rotor - see 6.2.

- Tension the rewind spring - see 6.5.

- Fit the fan housing.

STIHL 029, 039 49

7. AV HANDLE SYSTEM

7.1 Repair

Top:Removing annular buffer from fronthandle

Bottom:Removing lower annular buffer fromengine housing

Top:Fitting buffer in front handle1 = Groove

Bottom:Fitting buffer in engine housing1 = Groove

Top:Removing plug

Bottom:Fitting buffer in engine housing1 = Groove

- Pry the plug out of the upperannular buffer. Remove upperannular buffer from the enginehousing.

- Push the annular buffer into theengine housing from outside until itsannular groove engages over theedge of the housing.

Assembly is now a reversal of thedisassembly sequence.

- Push the annular buffer into the fronthandle (from inside) until its grooveengages over the housing rib.

- Push the lower annular buffer intothe engine housing until its grooveengages over the housing rib.

Note: To replace the upper annularbuffer it is necessary to remove theexhaust muffler and handle housing,see 4.1 and 8.1.1.

Rubber anti-vibration buffers areinstalled between the handle housingand engine housing. Damagedrubber buffers (annular buffers) mustalways be replaced.

- Remove the front handle see 8.1.

- Remove both annular buffersfrom the front handle.

- Push the lower annular bufferout of the engine housing.

STIHL 029, 039 50

- Take the lower mounting screwsout of the front handle.

- Remove the plugs from the annularbuffers on the front handle.

- Take out the front handle mountingscrews.

- Pull the front handle down and offthe handle housing, and then takeit away to the rear.

Assemble in the reverse sequence.

- Remove the front handle see 8.1.

- Remove the carburetor see 11.2.

- Slip the washer off the mountingstuds and take the sleeve out ofthe manifold.

- Pull the short circuit wire's con-nector sleeve out of the switchshaft.

Top:1 = Washer2 = Sleeve

Bottom:Withdrawing short circuit wire

Top:Front handle mountingscrews

Bottom:Removing the front handle

8. HANDLE HOUSING

8.1 Front Handle

Top:Lower mounting screws on fronthandle

Bottom:Plugs

8.1.1 Removing and InstallingHandle Housing

STIHL 029, 039 51

Top:Removing annular buffer

Bottom:Removing handle housing andpushing out manifold at same time

Top:Removing grommet

Bottom:Removing the impulsehose

Top:Ground wire

Bottom:Plug

- Pull the ground wire off thecontact spring.

- Ease the plug out of the annularbuffer on the hand guard.

- Push the annular buffer out of theengine housing.

- Pull the handle housing slightlyforward and push the manifoldthrough the handle housingopening at the same time.

- Ease the grommet for the groundand short circuit wires out of thehandle housing.

- Remove the impulse hose fromthe handle housing.

- Remove the handle housing andpull the ground and short circuitwires out of the bore at the sametime.

Assembly is a reversal of thedisassembly sequence.

STIHL 029, 039 52

Top:1 = Bore for impulse hose2 = Grommet for ground and short circuit

wires3 = Impulse hose4 = Fuel hose

Bottom:String around manifold

Top:Pulling manifold into handlehousing intake opening

Bottom:Pulling impulse hose into position

Top:Annular groove

Bottom:Correct position of ground and short circuitwires

- Wind a piece of string (about 15cm / 6" long) around the back ofthe manifold flange and pass theends through the intake opening.

- Press the intake opening of thehandle housing against the mani-fold and pull the ends of the stringoutward at the same time. Themanifold flange is pulled throughthe handle housing intake openingwithout being damaged.

Note: Pay special attention to thefollowing points.

- Place the handle housing in posi-tion and thread the ground and shortcircuit wires through the bore. Fit thegrommet in the bore.

- Position impulse hose in bore andpass the fuel hose through thelower slot.

- Pull the impulse hose outward isuntil its bead is in front of thehousing.

- Push the annular buffer into theengine housing until its grooveengages the housing rib.

- Position the ground and shortcircuit wires correctly in thehandle housing (see illustration)and push them into their retainers.

STIHL 029, 039 53

9. MASTER CONTROL

9.1 Switch Shaft

The main part of the Master Controlis the switch shaft with an integrallymolded multi-function operatinglever, a molded seat for the contactspring and connector sleeve andthree levers.

The thumb-operated MasterControl lever moves the switchshaft to select the requiredfunction.

The following positions can beselected with the Master Controllever (from the top down):

- STOP (short circuitcontact closed,ignition interrupted)

- RUN (normal operatingposition)

- START (warm start -starting throttle/choke shutter open)

- CHOKE (cold start -starting throttle/choke shutter closed)

- Remove the carburetor box cover -see 11.1.

- Set the Master Control to "CHOKE".

- Take the short circuit wire out of itsseat on the switch shaft.

- Pull the connector sleeve of theshort circuit wire out of the switchshaft.

- Lever the switch shaft out ofits pivot mount.

- Pull the switch shaft out ofthe bore.

Installation is a reversal of theremoval sequence.

Note: The contact spring must beheld up while installing the switchshaft.

Top:Withdrawing the switch shaft

Bottom:Holding the contact spring up

Top:Removing connector sleeve1 = Seat on switch shaft

Bottom:Detaching the switchshaft

Positions of MasterControl lever:1 = STOP2 = RUN3 = START (warm start)4 = CHOKE (cold start)

STIHL 029, 039 54

9.2 Interlock Lever/Throttle Trigger

- Push the interlock lever into theslots.

Note: The torsion spring must beunder the interlock lever and engagethe notch.

- Press the interlock lever down-ward. Push the throttle triggerupward and move the MasterControl lever to the "CHOKE"position.

- Fit the handle molding so that itengages behind the lugs asshown in the illustration. Securewith screw.

- Disconnect the throttle rod fromthe trigger.

- Use a 4 mm (5/32") drift to driveout the cylindrical pin. Removethe throttle trigger and torsionspring.

- Position the torsion spring on thethrottle trigger -long leg of springmust face upward.

- Fit the throttle trigger so that theseat for the throttle rod points upward. Push the cylindrical pin intoposition.

- Remove the carburetor box cover.

- Move Master Control to coldstart position (CHOKE).

- Take out the handle moldingfastening screw. Lift away thehandle molding.

- Take the interlock lever out of itsseat.

- Move Master Control lever to"RUN" position.

Top:1 = Interlock lever2 = Throttle trigger3 = Master Control lever

Bottom:Fitting handle molding

Top:1 = Cylindrical pin2 = Torsion spring3 = Throttle trigger

Bottom:1 = Torsion spring2 = Throttle lever

Top:Withdrawing interlock lever

Bottom:Disconnecting throttle rodfrom throttle trigger.

STIHL 029, 039 55

10. CHAIN LUBRICATION

10.1 Suction Hose/Pickup Body

Impurities gradually clog the finepores of the filter with tiny particles ofdirt. This prevents the oil pump fromsupplying sufficient oil to the bar andchain. In the event of problems withthe oil supply, first check the oil tankand the pickup body.Clean the oil tank if necessary.

- Remove the front handle see 8.1.

- Remove the clutch - see 3.2.

- Drain the oil tank.

- Push the suction hose off thenipple on the oil pump.

- Pull the suction hose out of theengine housing.

- Pull the suction hose with pickupbody out of the housing.

- Pull the pickup body out of thehose.

- Use side cutters or similar tool toremove the strainer from theconnector.

- Wash the strainer and pickup bodyin white spirit and, if possible, blowout with compressed air.

Important: Always replace a damagedpickup body.

Top:Removing the strainer

Bottom:1 = Hose2 = Connector3 = Strainer

Top:Removing suction hose from oilpump nipple

Bottom:Pulling out the suction hose

Top:Pulling out suction hose withpickup body

Bottom:Pulling pickup body out of hose

STIHL 029, 039 56

10.3 Removing and Installingthe Oil Pump

Top:Oil filler cap

Bottom:Pushing bead of suctionhose into position

Top:Vent valve

Bottom:Installed position of valve a =approx. 1 mm (3/64")

Top:Removing the worm

Bottom:Removing suction hose from oilpump nipple

10.2 Vent Valve

- Remove the clutch - see 3.2.

- Pull the worm and drive spring offthe crankshaft stub.

- Take the spring off the worm.

- Push the suction hose off thenipple on the oil pump.

A valve is installed in the tank wall tokeep internal tank pressure equal toatmospheric pressure.

- Drain the oil tank.

- Use a 7 mm (9/32") dia. drift tocarefully drive the vent valve intothe engine housing and thenremove it from the oil tank.

- Carefully press in the new valveuntil it is about 1 mm (3/64") belowthe face of the housing.

- Remove the oil filler cap and thecap retainer. Flush out the oil tank.

Assembly is a reversal of thedisassembly sequence.

Note: Coat the bead of the suctionhose with oil to simplify fitting.

STIHL 029, 039 57

10.4 Servicing theOil Pump

- Take out the oil pump mountingscrews.

- Push the oil pump to one side andease the elbow connector off thenipple.

- Remove the oil pump.

- Take the O-ring off the nipple andfit a new one.

- Place the pump in position andline it up.

- Slip the assembly sleeve over thecrankshaft stub.

- Fit the mounting screws by hand.

- Place the press sleeve in position.Tap the end of the press sleevelightly to seat the pump housing.

- Tighten screws to 4.0 Nm (3 Ibf.ft).

- Fit the worm.

- Install the clutch - see 3.3.

Always check the suction hose andpickup body before disassembling theoil pump.

- Remove the oil pump - see 10.3.

- Swing the elbow connector to oneside and pull it out of the housing.

- Remove the O-ring from the elbowconnector.

- Use a 2 mm (5/64") dia. drift to driveout the spring pin. Pull the controlbolt out of the housing and removethe O-rings.

- Take out the pump piston with helicalspring and washers.

- Wash all parts in white spirit. Inspectthe parts for damage and replace asnecessary.

Assembly is a reversal of thedisassembly sequence.

Note: Always install new O-rings. Coatthe pump piston and worm with grease,- see 12.2, before installing.

1 = Pump piston2 = Washer3 = Helical spring4 = Washer5 = O-ring6 = Elbow connector7 = Spring pin8 = O-ring9 = Control bolt

Top:1 = Assembly sleeve 1122 893 46002 = Press sleeve 1127 893 2400

Bottom:Press sleeve in position

Top:Removing the oil pump1 = Elbow connector

Bottom:O-ring

STIHL 029, 039 58

11. FUEL SYSTEM

11.1 Air Filter

Top:Twist lock on carburetor box cover

Bottom:1 = Prefilter2 = Slotted nuts Separating two halves of air filter

Master Control in"CHOKE" position

The air filter's function is to remove anydust and dirt sucked in with thecombustion air and thus help reducewear on engine components to aminimum.

Dirty and clogged air filters reduceengine power, increase fuel con-sumption and make starting moredifficult.

The air filter should always becleaned when engine power beginsto drop off.

Before removing the filter, close thechoke shutter to prevent dirt fallinginto the carburetor - press down theinterlock lever and move MasterControl down to cold start position(CHOKE).

- Turn twist lock on carburetor box cover one quarter turn counter-clockwise and take away the cover.

- Clean away any loose dirt fromaround the filter.

- Push the prefilter up a little or takeit out of the recesses in the handlehousing.

- Unscrew the slotted nuts.

- Pull the air filter off the studs.

- Separate the two halves of thefilter.

- Wash both parts of the filter in afresh, non-flammable cleaningsolution (e.g. warm soapy water)and, if possible, blow clear withcompressed air. Encrusted dirtshould be softened by immersingthe filter in the cleaning solution.

Important: Do not clean flocked airfilters with compressed air, brushesor rags.

Note: If the filter is damaged,replace it immediately.

Installation is a reversal of theremoval sequence.

STIHL 029, 039 59

11.2 Removing and Installingthe Carburetor

The all-position diaphragm carburetorconsists of a fuel pump and the actualcarburetor. Although the fuel pumpshares a common housing with thecarburetor, it operates as a complete-ly separate and independent unit.

Troubleshooting chart - see 2.6.

- Remove the air filter - see 11.1.

Note: For removal of carburetor onmachines with automatic choke -see 11.6.8.

- Unscrew the flanged lock nutsfrom the mounting studs.

- Disconnect the throttle rod fromthe throttle trigger.

- Disconnect the throttle rod fromthe throttle shaft.

- Remove the grommet from theadjusting screws and pull it out ofthe handle housing.

- Pull the carburetor off the studsand pry the fuel hose off theelbow connector at the same time.

Installation is a reversal of theremoval sequence.

Note: Check that sleeve (in manifold)and washer are in place before fittingthe carburetor in position. Push thefuel hose on to the elbow connectoron left side of carburetor. After fitting,check that elbow connector onunderside of carburetor is properlyengaged in impulse hose. Fit newflanged lock nuts and torque themdown to 3.2 Nm (2.4 Ibf.ft).

Top:Detaching throttle rod

Bottom:Removing grommet for adjusting screws

Top:Flanged lock nuts

Bottom:Detaching throttle rod

Removing the carburetor1 = Fuel hose

STIHL 029, 039 60

11.4 Servicing theCarburetor

11.3 Leakage Testing theCarburetor

Fastening screw on fuelpump end cover

Pressure testing carburetor withcarburetor/crankcasetester 1106 850 2905

Zama and Walbro carburetors ofalmost identical construction areinstalled in these machines. Theservicing procedures for the Zamacarburetor are described below.Differences in individual parts aredescribed separately.

It is advisable to check the service-ability of the fuel pump whenever thecarburetor is removed for repair.

- Remove the carburetor see 11.2.

- Unscrew the fuel pump endcover and take it off.

- Close the vent screw on the rubberbulb and pump air into the carburetoruntil the pressure gauge shows areading of approx. 0.4 bar (5.8 psi).

If this pressure remains constant, thecarburetor is airtight. However, if itdrops, there are two possible causes:

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.

The carburetor can be tested forleaks with the carburetor andcrankcase tester.

- Remove the carburetor, - see 11.2.

- Connect tester's pressure hose toelbow connector on side of car-buretor. Note that a separate nippleand a length of fuel line are requiredto make this connection.

Top:Nipple 0000 855 9200fitted in fuel line1110 141 8600

Bottom:Fuel line on elbowconnector

STIHL 029, 039 61

- Remove the gasket and pumpdiaphragm.

Note: The diaphragm and gasketoften stick to the cover or carburetorbody. If this is the case, takeparticular care when separatingthem.

- If the fuel strainer in the pumpside of the carburetor body isdirty, use a scriber to remove itand then clean it.

Important: If the fuel strainer isdamaged, fit a new one.

In such a case the fuel pickup bodyshould also be inspected and replacedif necessary - see 11.8.

- To disassemble the carburetor,take out the screws of themetering chamber end cover andlift away the cover.

- Remove the metering diaphragmand gasket from the carburetorbody or the cover.

- Carefully separate the diaphragmand gasket.

Note: The diaphragms are the mostdelicate parts of the carburetor. Theyare subjected to continuous alternatingstresses and the material eventuallyshows signs of fatigue, i.e. thediaphragms distort and swell. Checkand replace if necessary.

Top:Metering diaphragm with gasketon end cover

Bottom:Separating gasket and diaphragm

Top:Fuel strainer in carburetor body

Bottom:Fastening screws of meteringchamber end cover

Top:Fuel pump end cover withgasket

Bottom:Pump diaphragm oncarburetor body

STIHL 029, 039 62

Top:Round head screw on control leverspindle (Zama)

Bottom:1 = Round head screw2 = Inlet control lever3 = Spindle4 = Helical spring5 = Inlet needle

Top:Damaged inlet needle

Bottom:Pressing out valve jet (Zama)

Top:Pressing out valve jet (Walbro)

Bottom:Carburetor adjusting screws

Note: On Walbro carburetor, use a4 mm (approx. 5/32") dia. drift topress the valve jet out of its seat.

- Remove the carburetor adjustingscrews.

Note: If there is an annular inden-tation on the sealing cone of the inletneedle, it will be necessary to replacethe inlet needle because it will nolonger seal properly. This is indicatedby constant flooding of the carburetoreven though the needle is clean.

- Use a 5 mm (approx. 3/16") dia.drift to press the valve jet out of itsseat in the direction of the venturiand wash it in white spirit.

- The inlet needle valve is located ina recess in the metering dia-phragm chamber. Remove theround head screw or collar screw.

- Remove the inlet control leverwith spindle, helical spring andinlet needle.

STIHL 029, 039 63

- Remove the sealing plate or plugfrom of the metering chamber.

Caution: The sealing plate or plug isdestroyed during removal. It should,therefore, only be removed if areplacement is available.

- The Walbro carburetor is equippedwith a fixed jet. To remove, use asuitable tool to ease the retainingring out of its seat and then takeout the fixed jet and O-ring.

- Wash the carburetor body and allserviceable parts in fresh whitespirit and blow clear with com-pressed air, paying special atten-tion to the bores and ports.

- To install the fixed jet, fit a newO-ring in the bore for the fixed jet.Press home the fixed jet (flat sideup) as far as stop and secure inposition with the retaining ring.

- When fitting the valve jet, makesure it is exactly vertical in thebore. Press it home until it isflush with the bottom of themetering chamber.

- Fit the inlet needle and the helicalspring in their respective bores.Insert spindle in the inlet controllever, engage clevis in annulargroove on the head of the inletneedle and tighten down the roundhead screw. Make sure that thehelical spring locates on the controllever's nipple.

- Check easy action of the inletcontrol lever.

Important: The top of the inlet controllever must be level with the bottom ofthe metering chamber. If necessary,use suitable pliers to carefully bend thelever.

- After fitting new sealing plate orplug, fill gap between carburetorbody and plate or plug with Loctite see 12.2.

Correct position of inletcontrol lever

Removing the fixed jet1 = Retaining ring2 = Fixed jet3 = O-ring

Top:Sealing plate (Zama)

Bottom:Sealing plug (Walbro)

STIHL 029, 039 64

Top:Locating pegs on body

Bottom:Locating pegs on cover

- Unscrew the throttle shutterfastening screw.

- Use suitable pliers to pull thethrottle shutter out of the throttleshaft.

- Pry the E-clip off the end of thethrottle shaft.

- Withdraw the throttle shaft fromthe carburetor.

- Remove the torsion spring.

Note: Fit the end cover so that thetwo elbow connectors are pointingin the same direction.

- Refit the carburetor adjustingscrews.

- Carry out leakage test beforeinstalling the carburetor see 11.3.

Removing the throttle shaft:

Note: For machines with automaticchoke - see 11.6.10.

- Fit the gasket, metering dia-phragm and end cover. Themetering diaphragm and gasketare held in position by theintegrally cast pegs on thecarburetor body.

- Insert the fuel strainer at thepump side. Fit the pump dia-phragm, gasket and end coverand tighten down securely. Thepump diaphragm and gasketare held in position by theintegrally cast pegs on the endcover.

Top:E-clip

Bottom:Withdrawing throttle shaft

Top:Elbow connectors

Bottom:Throttle shutterfastening screw

STIHL 029, 039 65

- After fitting the throttle shaft,check that the torsion spring iscorrectly positioned.

- Fit the throttle shutter, roundnotch first, with the small borepointing to the throttle lever.

- Coat the fastening screw withLoctite, - see 12.2, and tightendown firmly.

Removing choke shaft:

Note: For machines with automaticchoke - see 11.6.10.

- Unscrew choke shutter fasteningscrew. Remove the choke shutter.

- Pry the E-clip off the end of thechoke shaft and withdraw theshaft from the carburetor.

- Remove the torsion spring.

Top:Fitting throttle shutter

Bottom:Choke shutter fasteningscrew

Top:Correct position of torsion spring(Zama)

Bottom:Correct position of torsion spring(Walbro)

Top:Withdrawing choke shaft

Bottom:Removing the torsion spring

STIHL 029, 039 66

11.5 Carburetor Adjustment

Top:Correct position of torsion spring(Zama)

Bottom:Correct position of torsion spring(Walbro)

Top:Fitting choke shutter (Zama)1 = Large bore2 = Small bore

Bottom:Fitting choke shutter (Walbro)1 = Round notch2 = Indentation

The carburetor has a standardsetting when it leaves the factory.

This is the optimum setting of thehigh speed adjusting screw for thebarometric pressure and climaticconditions at the factory (300 m/1000ft above sea level). It ensuresmaximum engine performance, fuelefficiency and the highest possiblereliability.

Standard setting:

H = High speed adjusting screwbacked off 1 full turn

L = Low speed adjusting screwbacked off 1 full turn

If the carburetor has to be adjustedfrom scratch, first carry out thestandard setting to obtain a startingpoint for fine tuning.

If no tachometer is available, do notturn the high speed adjusting screwbeyond the standard setting to makethe mixture leaner.

Note: Fit the choke shutter of Walbrocarburetor so that the round notchpoints toward the metering end coverand the indentations face inward.

- Coat the fastening screw withLoctite, - see 12.2, and tightendown firmly.

- Install the carburetor - see 11.2.

- After fitting the choke shaft,check that the torsion spring iscorrectly positioned.

- Position choke shutter of Zamacarburetor so that the large borepoints toward the metering endcover and the small bore towardthe lever on the choke shaft.

1 = High speed adjusting screw2 = Low speed adjusting screw3 = Idle speed adjusting screw

STIHL 029, 039 67

If the saw is used at high altitudes(mountains) or near sea level:

A slight correction may be necessary.

For corrections to high speed adjustingscrew (H):Use a tachometer - do not exceedmaximum permissible engine speed.Engine can be damaged by lack oflubricant and overheating.

Maximum engine speed with bar andproperly tensioned chain: 13,000 r.p.m.

- Check chain tension- Check air filter and clean

if necessary- Adjust idle speed correctly

(chain must not rotate)- Start the saw -

warm up the engine

Turn high speed adjustingscrew (H) and low speed adjustingscrew (L) clockwise for leanermixture at high altitudes or counter-clockwise for richer mixture at sea level.

Turn screws very slowly andcarefully - even slight adjustmentproduce a noticeable change inengine running behavior.

Chain runs while engine is idlingTurn the idle speed adjusting screw(LA) counterclockwise until the chainstops running - and then turn aboutanother quarter turn in the samedirection.

Erratic idling behavior, pooracceleration Idle setting too lean.Turn the low speed adjusting screw(L) counterclockwise until theengine runs and acceleratessmoothly.

Exhaust smokes at idle speedIdle setting too rich. Turn the lowspeed adjusting screw (L) clockwiseuntil the engine speed drops - andthen turn it back one quarter turn -and check that the engineaccelerates smoothly when you openthe throttle.

Corrections to high speed adjustingscrew:The setting of the high speed adjustingscrew (H) affects the maximum off-loadengine speed. If the setting is too lean,the maximum permissible engine speedwill be exceeded and increase the riskof engine damage.

Adjusting engine idle speed:A correction at the low speed (L)usually necessitates a change in thesetting of the idle speed adjusting screw(LA).

Engine stops while idlingTurn idle speed adjusting screw (LA)clockwise until the chain begins torun - then turn it back