STIH)
Contents 1. Introduction 3 2. Safety Precautions 4 3. Specifications 5 3.1 Engine 5 3.2 Fuel System 5 3.3 Ignition System 5 3.4 Chain Lubrication 5 3.5 Tightening Torques 6 4. Troubleshooting Chart 7
4.1 Clutch, Chain Drive, Chain Brake, Chain Tensioner 7 4.2 Rewind Starter 8 4.3 Chain Lubrication 9 4.4 Ignition System 10 4.5 Carburetor 11 4.6 Engine 13
5. Clutch, Chain Drive, Chain Brake and
Chain Tensioner 14 5.1 Clutch Drum / Chain Sprocket 14 5.2 Replacing the Chain Catcher 15 5.3 Clutch 15 5.4 Chain brake 17 5.4.1 Checking correct operation 17 5.4.2 Removing 18 5.4.3 Installing 20 5.5 Chain Tensioner 22
5.6 Bar Mounting Studs 23
6. Engine 24 6.1 Muffler / Spark Arresting Screen 24 6.2 Leakage Test 25 6.2.1 Preparations 26 6.2.2 Pressure Test 27 6.2.3 Vacuum Test 27 6.3 Oil Seals 28
6.4 Removing the shroud 30 6.5 Cylinder and Piston 30
6.5.1 Removing 30 6.5.2 Installing 32 6.6 Piston Rings 35 6.7 Crankcase 35 6.7.1 Removing the crankshaft 35 6.7.2 Installing the crankshaft 38 6.8 Decompression Valve 43 7. Ignition System 44 7.1 Ignition Module 44 7.1.1 Ignition Timing 44 7.1.2 Removing and Installing 45
7.1.3 Testing the ignition
system 46
7.2 Ignition Lead /
Spark Plug Boot 47
7.3 Flywheel 48 7.3.1 Removal 48 7.3.2 Installation 49 7.4 Stop switch 49 7.5 Wiring harness 49 7.5.1 Testing Wiring Harness 50 7.6 Ignition System Troubleshooting 51 8. Rewind Starter 54 8.1 General 54 8.2 Removing and Installing 54 8.3 Pawls 54 8.4 Rope Rotor 55 8.5 Starter rope 55 8.5.1 Tensioning 56
8.6 Starter Rope Guide
Bushing 57
8.7 Replacing the
Rewind Spring 58
9. AV handle system 59
10. Single lever master control / handle system 60 10.1 Switch shaft 60 10.2 Throttle Trigger / Interlock Lever 61 11. Chain Lubrication 62 11.1 Pickup Body / Suction Hose 62 11.2 Valve 63 11.2.1 Cleaning 63 11.2.2 Replacing 63 11.3 Oil pump 64 11.3.1 Removing and installing 64 11.3.2 Servicing 64 12. Fuel System 65 12.1 Air Filter 65 12.2 Carburetor 66 12.2.1 Removing and Installing 66 12.2.2 Leakage Test 68 12.3 Servicing the Carburetor 68 12.3.1 Metering Diaphragm 68 12.3.2 Inlet Needle 69 12.3.3 Fixed Jet 70 12.3.4 Pump Diaphragm 70 12.4 Adjustment (carburetor
without limiter caps) 71 12.4.1 Adjustment (carburetor
with limiter cap) 72 12.4.2 Basic Setting (carburetor
with limiter cap) 73
12.5 Tank Vent 74
12.6 Pickup Body 74
12.7 Fuel Hose 75
Contents
13. Carburetor Heating 79
13.1 Troubleshooting
Chart 80
13.2 Heating element with thermostatic switch 81 14. Handle Heating System 81 14.1 Troubleshooting 81 14.1.1 Troubleshooting Chart 83 14.1.2 Test Connections
and Test Values 85
14.2 Heater switch 86 14.3 Heating element in front handle 86 14.4 Heating element in front handle 87 14.5 Generator 88 15. Special Servicing Tools 89 16. Servicing Aids 91
This service manual contains detailed descriptions of all the typical repair and servicing procedures for this power tool. You should make use of the illustrated parts lists while carrying out repair work. They show the installed positions of the individual components and assemblies. Refer to the latest edition of the relevant parts list to check the part numbers of any replacement parts. A fault on the machine may have several causes. To help locate the fault, consult the chapter on "Troubleshooting" and the "STIHL Service Training System".
Refer to the "Technical Information” bulletins for engineering changes which have been introduced since publication of this service manual. Technical information bulletins also supplement the parts list until an updated edition is issued.
The special tools mentioned in the descriptions are listed in chapter "Special Servicing Tools" of this manual. Use the part numbers to identify the tools in the "STIHL Special Tools" manual which lists all the special servicing tools currently available from STIHL.
Symbols are included in the text and pictures for greater clarity.
The meanings are as follows: In the descriptions:
: = Action to be taken as shown in the illustration (above the text)
– = Action to be taken that is not shown in the illustration (above the text)
+= Situation applies as from serial No. *= Situation applies up to serial No. In the illustrations: A Pointer aDirection of movement b 4.2
Reference to another chapter, i.e. chapter 4.2 in this example. Service manuals and technical information bulletins are intended exclusively for the use of properly equipped repair shops. They must not be passed to third parties.
Servicing and repairs are made considerably easier if the clamp (1) 5910 890 2000 is used to mount the machine on assembly stand (2) 5910 890 3100 so that one clamp screw engages the outer 10 mm (0.39 in) hole (3) in the assembly stand.
To service the underside of the machine (e.g. remove the front handle), turn it upside down and mount it so that one clamp screw engages the inner 10 mm
(0.39 in) hole in the assembly stand. Pull the hand guard back against the front handle for this purpose.
Always use original STIHL replacement parts.
They can be identified by the STIHL part number,
the STIH) logo and the STIHL parts symbol (
This symbol may appear alone on small parts.
If the engine is started up in the course of repairs or maintenance work, observe all local and country-specific safety regulations as well as the safety precautions and warnings in the instruction manual. Gasoline is an extremely flammable fuel and can be explosive in certain conditions.
Improper handling may result in burns or other serious injuries.
Warning!
Do not bring any fire, flame, spark or other source of heat near the fuel. All work with fuel must be performed outdoors only. Spilled fuel must be wiped away immediately.
3. Specifications
3.1 Engine
Displacement: 70.7 cm3 (4.31 cu.in)
Bore: 50 mm (1.97 in)
Stroke: 36 mm (1.42 in)
Engine power to ISO 7293: 4 kW (5.4 bhp) at 9,500 rpm Max. permissible engine speed
with bar and chain: 13,500 ± 150 rpm
Idle speed: 2,500 1 rpm
Clutch: Centrifugal clutch with three unlined
clutch shoes
Clutch engages at: 3,500 rpm
Crankcase leakage test
at gauge pressure: pü = 0.5 bar (7.25 psi)
under vacuum: pu = 0.5 bar (7.25 psi)
3.2 Fuel System
Carburetor leakage test
at gauge pressure: pü = 0.8 bar (11.6 psi)
Operation of tank vent at gauge
pressure: pü = 0.3 bar (4.35 psi)
Fuel: as specified in instruction manual
3.3 Ignition System
Air gap between ignition module
and fanwheel: 0.15...0.3 mm (0.006...0.12in)
Spark plug (suppressed): Bosch WSR 6F
NGK BPMR 7A
Electrode gap: 0.5 mm (0.02 in)
3.4 Chain Lubrication
Fully automatic, speed-controlled oil pump with rotary piston
Oil delivery rate: 8...18 cm3/min
3.5 Tightening Torques
DG screws are used in polymer and light metal components. These screws form a permanent thread when they are installed for the first time. They can be removed and installed as often as necessary without impairing the strength of the screwed assembly, providing the specified tightening torque is observed.
For this reason it is essential to use a torque wrench.
Fastener Thread size For component Torque Remarks
Nm (lbf ft)
Screw IS-M5x20 Crankcase 11.5 (8.48)
Screw IS-M5x20 Cylinder 11.5 (8.48)
Screw IS-M5x16 Muffler, lower casing to cylinder 11.0 (8.11) 1)
Screw IS-M5x6 Muffler, upper casing top 6.5 (4.79) 1)
Screw IS-M5x16 Muffler top 11.0 (8.11) 1)
Screw IS-M5x18 Muffler bottom 15.0 (11.06) 1)
Screw IS-M5x20 Ignition module 7.0 (5.16) 2)3)
Screw IS-M4x16 Shroud 4.0 (2.95)
M12x1 L Carrier (clutch) 50.0 (36.88)
M14x1,25 Spark plug 25.0 (18.44)
Nut M5 Carburetor 3.5 (2.58)
Screw IS-M4x16 Annular buffer plate 5.0 (3.69)
Screw IS-M5x12 Spiked bumper top (with nut) 7.5 (5.53)
Screw IS-M5x16 Spiked bumper bottom (chain catcher) 7.5 (5.53)
Screw IS-M3,5x12 Generator 2.0 (1.48) 1)
Screw M4x8 Cover, chain tensioner 3.0 (2.21)
Screw IS-M4x12 Oil pump 3.5 (2.58)
Screw IS-M4x12 Cover, chain brake 3.0 (2.21)
Screw IS-M4x12 Brake band 3.0 (2.21) 1)
Screw IS-M4x16 Fan housing 4.0 (2.95) 2)
Screw M4x8 Side plate, inner 3.0 (2.21)
Nut M8x1 Crankshaft (flywheel) 33.0 (24.34)
M10x1 Decompression valve 14.0 (10.33)
Collar stud M8x21,5 Bar mounting 23.0 (16.96) 1)
Polymer screw IS-P6x26,5 Annular buffer, top 5.5 (4.06)
Polymer screw IS-P6x19 Annular buffer, bottom 5.5 (4.06)
Polymer screw IS-P6x19 Front handle, top 8.0 (5.90) 4)
Polymer screw IS-P6x19 Front handle, bottom 8.0 (5.90) 4)
Screw assy. IS-M4x16 Hand guard left, fan housing 4.0 (2.95)
Remarks:
1) Secure screw with Loctite 270 2) Secure screw with Loctite 242
4. Troubleshooting Chart
4.1 Clutch, Chain Drive, Chain Brake, Chain Tensioner
Condition Cause Remedy
Saw chain stops under load at full throttle
Clutch shoes badly worn Replace clutch shoes
Clutch drum badly worn Install new clutch drum
Brake band stuck Check freedom of movement
and function of brake band. Saw chain rotates at idle speed Engine idle speed too high Adjust idle speed screw
(counterclockwise) Clutch springs stretched or fatigued Replace clutch springs Clutch spring hooks broken Replace clutch springs Loud noises Clutch springs stretched or fatigued Replace all clutch springs
Needle cage damaged Fit new needle cage
Clutch shoe retainer broken Fit new retainer Clutch shoes and carrier worn Install new clutch
Chain sprocket wears rapidly Chain not properly tensioned Tension chain as specified
Wrong chain pitch Fit chain of correct pitch
Insufficient chain lubrication Check chain lubrication
Chain sprocket worn Fit new chain sprocket
Saw chain does not stop immediately when brake is activated
Brake spring stretched or broken Fit new brake spring
Brake band stretched, worn or
4.2 Rewind Starter
Condition Cause Remedy
Starter rope broken Rope pulled out too vigorously as far as stop or over edge, i.e. not vertically
Fit new starter rope
Normal wear Fit new starter rope
Starter rope does not rewind Rewind spring broken Fit new rewind spring
Spring overtensioned – no reserve
when rope is fully extended Fit new rewind spring
Very dirty or corroded Clean or replace rewind spring Starter rope can be pulled out
almost without resistance (crankshaft does not turn)
Guide peg on pawls or pawls themselves are worn
Fit new pawls
Spring clip fatigued Fit new spring clip
Starter rope is difficult to pull and rewinds very slowly
Starter mechanism is very dirty Thoroughly clean complete starter mechanism
Lubricating oil on rewind spring becomes viscous at very low outside temperatures (spring windings stick together)
Coat rewind spring with a little standard solvent-based degreasant (containing no chlorinated or halogenated hydrocarbons), then pull rope carefully several times until normal action is restored
4.3 Chain Lubrication
Warning!
In the event of trouble with the chain lubrication system, check and rectify other sources of faults before disassembling the oil pump.
Condition Cause Remedy
Chain receives no oil Oil tank empty Fill up with oil
O-ring on oil line to crankcase
defective or oil line damaged Remove oil pump, fit a new O-ring and refit or replace the oil pump Oil inlet hole in guide bar is
blocked Clean oil inlet hole
Intake hose or pickup body (strainer) clogged or intake hose ruptured
Clean intake hose and pickup body (strainer) with standard solvent-based degreasant not containing chlorinated or halogenated
hydrocarbons / replace intake hose and pickup body
Valve in oil tank blocked Clean or replace valve Teeth on pump piston and/or worm
worn
Install new oil pump and/or new worm
Machine losing chain oil O-ring on oil line to crankcase
defective or oil line damaged Remove oil pump, fit a new O-ring and refit or replace the oil pump Piston bore in pump housing worn Install new oil pump
Oil pump delivers insufficient oil Adjusting screw and/or control
edge on pump piston worn Fit new adjusting screw and/or oil pump Piston bore in pump housing worn Install new oil pump
4.4 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!
Condition Cause Remedy
Engine runs roughly, misfires,
temporary loss of power Spark plug boot is loose Press boot firmly onto spark plug and fit new spring if necessary Spark plug sooted, smeared
with oil
Clean the spark plug or replace if necessary
Incorrect air gap between ignition
module and flywheel Set air gap correctly
Flywheel cracked or has other damage or pole shoes have turned blue
Install new flywheel
Ignition timing wrong, flywheel out of adjustment, key in flywheel has sheared off
Install new flywheel
Weak magnetization in flywheel –
pole shoes have turned blue Install new flywheel
No spark Check operation of Master Control
lever and ignition module
No spark Faulty insulation on ignition lead or
short circuit wire. Use ohmmeter to check ignition lead for break. If break is detected or high resistance measured, fit a new ignition lead
4.5 Carburetor
Condition Cause Remedy
Carburetor floods; engine stalls
Inlet needle not sealing. Foreign matter in valve seat or cone damaged
Remove and clean or replace the inlet needle, clean the fuel tank, pickup body and fuel line if necessary
Inlet control lever sticking on spindle
Free off inlet control lever
Helical spring not located on nipple
of inlet control lever Remove the inlet control lever and refit it correctly Perforated disc on diaphragm is
deformed and presses constantly against the inlet control lever
Fit a new metering diaphragm
Inlet control lever too high (relative to correct installed position)
Set inlet control lever flush with top edge of housing
Poor acceleration Idle jet too lean Rotate low speed screw (L)
counterclockwise (richer), no further than stop
Main jet too lean Rotate high speed screw (H)
counterclockwise (richer), no further than stop
Inlet control lever too low (relative to correct installed position)
Set inlet control lever flush with top edge of housing
Inlet needle sticking to valve seat Remove inlet needle, clean and refit
Diaphragm gasket leaking Fit new diaphragm gasket Metering diaphragm damaged or
shrunk Fit new metering diaphragm
Condition Cause Remedy Engine will not idle,
idle speed too high
Throttle shutter opened too wide by idle speed screw (LA)
Reset idle speed screw (LA) correctly
Oil seals/crankcase leaking Seal or replace oil seals/ crankcase
Engine stalls at idle speed Idle jet bores or ports blocked Clean jet bores and ports, and blow through with compressed air Idle jet too rich or too lean Set low speed screw (L)
correctly Setting of idle speed (LA)
incorrect – throttle shutter completely closed
Set idle speed screw (LA) correctly
Small plastic plate in valve jet
does not close Clean or renew valve jet
Engine speed drops quickly under load – low power
Air filter dirty Clean the air filter
Throttle shutter not opened fully Check actuation
Tank vent faulty Clean tank vent or replace if
necessary
Fuel pickup body dirty Clean the pickup body, fit a new filter
Fuel strainers dirty Replace the fuel strainers Leak in fuel line between tank and
fuel pump Seal connections or install a new fuel line Pump diaphragm damaged or
fatigued
Fit new pump diaphragm
Main jet bores or ports blocked Clean bores and ports
Setting of high speed screw (H)
too rich Rotate high speed screw (H) clockwise (leaner), no further than stop
4.6 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, stalls at idle speed, but operates normally at full throttle.
Oil seals in crankcase damaged Replace the oil seals
Crankcase leaking or damaged
(cracks) Seat or replace the crankcase
Leak in muffler Seal / replace muffler
Engine does not deliver full power
or runs erratically Piston rings worn or broken Replace piston rings
Muffler / spark arresting screen
carbonized Clean muffler (inlet and exhaust opening), replace spark arresting screen
Air filter insert soiled Replace air filter insert Fuel / impulse hose severely kinked
or damaged
Fit new hoses or position them free from kinks
Decompression valve sticking Replace the decompression valve Engine overheating Insufficient cylinder cooling.
Air inlets in fan housing blocked or cooling fins on cylinder very dirty
Thoroughly clean all cooling air openings and the cylinder fins.
Wear work gloves to protect your hands from injury.
: Unscrew the hex nuts (1) on the chain sprocket cover (2) and remove chain sprocket cover and guide bar (3). VA 138RA002
1
2
3
: Disengage the chain brake by pulling the hand guard towards the front handle.
VA
143RA004
: Remove the E-clip (1), washer (2) and rim sprocket (3) if fitted.
VA
148RA061
3
2
1
: Remove the clutch drum (1) with needle cage (2).
– Examine the needle cage for signs of damage.
VA
148RA062
1
2
: Inspect the clutch drum (1). If there are signs of serious wear on the inside diameter of the clutch drum (1), check the remaining wall thickness. If it is less than about 80% of the original thickness, fit a new clutch drum.
VA 148RA101 80% 100%
1
!
If the clutch drum has to be replaced, also check the brake band – b 5.4.2
5. Clutch, Chain Drive, Chain Brake
and Chain Tensioner
5.1 Clutch Drum / Chain Sprocket
If the clutch drum can be reused, clean and roughen the friction surface.
Reassemble in the reverse sequence.
Clean stub of crankshaft. Wash
VA
176RA330
needle cage, examine it for damage and replace if necessary. Lubricate needle cage with STIHL multi-purpose grease – b 16. – Rotate clutch drum / chain
sprocket and apply slight pressure at the same time until the oil pump drive spring engages in the slot on the circumference.
– Remove the chain sprocket cover – b 5.1
: Take out the screw (1) and remove the chain catcher (2). Reassemble in the reverse sequence.
VA
176RA000
2
1
Troubleshooting chart – b 4.1– Remove the clutch drum/chain sprocket – b 5.1
: Release twist lock (1) on
carburetor box cover (2) and lift it off.
VA
176RA002
1
2
: On machines with HD air filter, draw air guide (1) off to the rear.
VA
176RA250
1
5.2 Replacing the
: On machines with box filter, remove air filter (1).
– Pull the boot off the spark plug and unscrew the spark plug.
VA
176RA003
1
: Close the decompression valve if fitted, carefully prising the button (2) upwards for this purpose.
: Push the locking strip (1) 0000 893 5903 into the spark plug hole so that "OBEN-TOP"
VA
175RA001
1
2
faces up.
: Unscrew the clutch (1) from the crankshaft clockwise (left-hand thread).
VA
148RA068
Disassembling the clutch
: Use hook (2) 5910 890 2800 to remove the clutch springs (1). – Pull the clutch shoes off the
carrier.
VA
208RA028
2
1
: Pull the retainers off the clutch shoes.
VA
208RA031
– Clean all parts.
– Replace any damaged parts.
VA
208RA026
Assembly
: Slip the retainers onto the clutch shoes.
VA
: Fit the clutch shoes over the arms (1) of the clutch carrier so that the series number (2) is on the same side as the longer hexagon (3).
VA
146RA208
2
1
3
: Clamp the clutch in a vise.
VA
208RA030
: Attach one end of each spring (1) to the clutch shoes.
: Use the hook (2) 5910 890 2800 to attach other end of the spring and press it firmly into the clutch
VA
208RA033
1
2
: Screw home the clutch, turning counterclockwise, and tighten it down firmly – b 3.5
– Remove locking strip from the cylinder.
– Turn in the spark plug and tighten
VA
135RA024
it down firmly – b 3.5
– Plug the boot onto the spark plug. – Refit the shroud.
– Fit the clutch drum / chain sprocket – b 5.1
Ensure that the grooves in the shroud are correctly positioned when assembling the parts.
The chain brake is one of the most important safety devices on the chainsaw. Its efficiency is measured in terms of the chain braking time, i.e. the time that elapses between activating the brake and the saw chain coming to a complete standstill. The shorter the braking time, the better the efficiency and protection offered against being injured by the rotating chain. Contamination (with chain oil, chips, fine particles of abrasion, etc.) and smoothing of the friction surfaces of the brake band and clutch drum impair the coefficient of friction. This, in turn, reduces the frictional forces and thus prolongs the braking time. A fatigued or stretched brake spring has the same negative effect.
– Start the engine.
– With the chain brake activated (locked), open the throttle wide for a brief period (max. 3 seconds) – the chain must not rotate.
– With the chain brake released, open the throttle wide and activate the brake manually – the chain must come to an abrupt stop.
The braking time is in order if deceleration of the saw chain is imperceptible to the eye.
If the chain brake does not operate properly, see troubleshooting chart – b 4.1.
5.4 Chain brake 5.4.1 Checking correct
– Remove the chain sprocket cover and guide bar – b 5.1
– Remove the clutch – b 5.3
: Take out the screw (1) of the inner side plate (2) and remove the side plate.
– Engage the chain brake by pushing the hand guard away from the front handle.
VA
138RA004
1
2
: Take out the screws (arrows). – Remove the cover.
– Release the brake spring by pushing the hand guard forwards.
VA
175RA002
: Carefully ease the brake spring (1) off the anchor pin and remove it from the bell crank (2).
VA
176RA027
1
2
: Take out the screw (arrow) on the brake band.
VA
176RA028
: Ease the brake band out of the engine housing.
VA
176RA029
: Remove the brake band from the stubs (1) on the crankcase. : Unhook the brake band from the
bell crank (2). VA 175RA003
1
2
5.4.2 RemovingInstall a new brake band if: – there are noticeable signs of
wear (large areas on inside diameter and/or parts of outside diameter) and
– its remaining thickness is less
VA
176RA031
than 0.6 mm (0.02 in). This minimum thickness must remain at all points.
: If the brake band can be reused, clean and roughen the entire friction surface.
: Take out the screw (1).
VA
176RA005
1
: Remove the E-clip (arrow).
VA
176RA032
: Carefully pry the hand guard (1) and bell crank (2) off the pivot pins and remove all parts. : Draw the bell crank out of the
hand guard.
VA
176RA033
1
2
: Remove the E-clip (1).
: Disconnect the spring (2) and remove the cam lever (3). – Examine the parts and replace
any defective elements.
VA 176RA034
3
1
4
2
– Clean the entire installation area of the chain brake.
– If the groove on the pin (4) for the brake spring is worn, the pin must be replaced.
: Drive the pin (1) out of the crankcase with a drift in the direction indicated.
Do not drive out the pin in the other direction as this would damage the annular bead which was formed in the crankcase bore when the pin
VA
176RA035
1
was originally installed. In such a case neither the new anchor pin nor the brake spring would locate properly. Furthermore, the
crankcase could be damaged in this way and possibly impair correct operation of the chain brake.
– Before installing the new pin, coat its knurled shank with Loctite – b 16.
– Position the new pin in the bore so that the knurling on the pin meshes with the existing knurling in the bore. Turn pin back and forth as necessary.
: Carefully tap home the pin squarely to obtain dimension "a" (about 4.3–4.7 mm)
(0.17–0.19 in).
The pin must be driven home absolutely square.
VA
176RA036
a
– Install the cylinder – b 6.5.2 – Coat all sliding and bearing
points with STIHL multipurpose grease – b 16.
: Fit the cam lever (1). : Fit the E-clip (2).
1 1 21
1
2
VA 176RA037: Hook the spring (1) into the pivot pin (2) and cam lever (3).
– Examine the reflector foil on the hand guard and replace it if necessary. VA 176RA038
2
1
3
: Slide the bell crank into the opening at the side of the hand guard.
The short end of the lever (arrow) faces the upper part of the hand guard.
VA
176RA040
: Position the bearing boss of the hand guard (1) against the pivot pin and fit the other side over the housing.
: Position the bell crank (2) against the pivot pin.
VA
176RA041
1
3
2
: Lightly press the cam lever (3) down, pressing the hand guard and bell crank onto the pivot pins at the same time.
– Tighten the hand guard screw – b 3.5
: Check that the cam lever is correctly positioned on the sliding surface (arrow) of the bearing boss.
VA
176RA042
: Secure the bell crank with the E-clip (arrow).
– Coat the brake band with chain oil to protect it against corrosion and to soften the "hard blow" of the brake when braking for the first few times.
VA
176RA043
: Hook the brake band into the bell crank (arrow).
– Route the brake band round behind the stubs on the crankcase.
176RA044
VA
: Push the brake band into the slot. – Turn the screw in with Loctite –
b 16.
– Tighten down the screw – b 3.5
VA
176RA045
: Turns of brake spring must be tightly against one another in the relaxed condition. If this is not the case, replace the brake spring. : Check correct position of the
protective tube a = 20 mm (0.79 in) a a b VA 176RA046 b = 32 mm (1.26 in)
: Hook the brake spring into the slot on the bell crank (arrow).
VA
176RA047
: Use the assembly tool (2) 1117 890 0900 to attach the brake spring (1) to the anchor pin.
VA
176RA048
1
2
– Fit the cover.
: Turn in the screws (arrows) and tighten them down – b 3.5 – Fit the clutch drum / chain
sprocket – b 5.1
VA
175RA002
: Slide the side plate (2) onto the collar screws and position it against the crankcase.
: Insert the screw (1) and tighten it down.
– Fit the guide bar and chain
VA
138RA004
1
2
sprocket cover, then tighten down the nuts on the chain sprocket cover – b 3.5 – Check correct operation of the
chain brake – b 5.4.1
– Remove the inner side plate – b 5.4.2
: Use a screwdriver to turn the spur gear clockwise until tensioner slide (1) butts against the thrust pad (2).
VA
176RA052
2
1
: Remove the retainer (1). : Take out the screw (2).
VA
176RA053
1
2
: Remove the cover plate.
VA
176RA054
: Pull out the spur gear.
VA
176RA055
: Pull out the tensioner slide with adjusting screw and thrust pad.
VA
176RA056
: Inspect the teeth on the spur gear and adjusting screw (1), and replace both parts if necessary. To do this, pull off the thrust pad (2) and unwind the adjusting screw from the tensioner
slide (3). VA 176RA057
3
1
2
Always replace the adjusting screw and spur gear as a matching pair. Reassemble in the reverse sequence.
– Before installing, lubricate teeth on adjusting screw and spur gear with grease – b 16.
: Check that the O-ring (arrow) is fitted in the spur gear and lubricate it with oil before installing the spur gear.
VA
176RA058
– Remove chain sprocket cover and cutting attachment – b 5.1 : Push stud puller (1)
5910 893 0501 over the collar stud as far as it will go. Use a 15 mm (0.60 in) wrench to unscrew the collar stud
VA
176RA117
1
counterclockwise.
– Before installing, coat thread of collar stud with LOCTITE – b 16.
– Fit the collar stud and tighten it down firmly – b 3.5
Always check and, if necessary, repair the fuel system, carburetor, air filter and ignition system before looking for faults on the engine. Troubleshooting chart – b 4.6
: Take out the screws (arrows). – Remove the exhaust casing.
VA
176RA006
: Take out the screws (arrows). – Remove the inlet casing. – Remove the gasket and heat
shield.
– Check the spark arresting screen
VA
175RA004
if fitted, bend the retaining lugs back and pull out the spark arresting screen (except on the MS 440 Magnum).
– Clean the spark arresting screen or replace it if necessary.
On the MS 440 Magnum, proceed as follows to clean the spark arresting screen:
MS 440 Magnum only
: Take out the screws (1). Remove the cover plate (2).
VA
176RA059
1
2
: Remove the spark arresting screen (arrow).
– Clean the spark arresting screen or replace it if necessary.
Versions with catalytic converter only
VA
176RA060
: If there are cracks in the
honeycomb structure (1) or if the steel jacket enclosing the honeycomb is defective, the catalytic converter must be replaced in order to prevent damage to the engine.
VA
176RA324
1
6. Engine
6.1 Muffler / Spark Arresting Screen
: Examine the reflector foil (arrow) and replace it if necessary – b 6.7.2
VA
176RA061
: Fit the heat shield (1) in position. : Position a new gasket (2) with the
bead (3) facing outwards. – Coat the screw threads with
Loctite – b 16. VA 176RA008
2
1
3
– Tighten down the screws – b 3.5 When assembling the parts, ensure that size M6x20 screws are fitted at the bottom and size M5x6 screws at the top to secure the exhaust casing.
Versions with catalytic converter only
: Fit M6x30 screws (arrows) with tensioning gear.
: Insert M5x30 screw (1) with sleeve.
VA
176RA323
1
Defective oil seals and gaskets or cracks in castings are the usual causes of leaks. Such faults allow supplementary air to enter the engine and upset the fuel-air mixture.
This makes adjustment of the prescribed idle speed difficult, if not impossible.
Moreover, the transition from idle speed to part or full throttle is not smooth.
The crankcase can be checked thoroughly for leaks with the carburetor and crankcase tester and the vacuum pump.
– Remove the decompression valve, if fitted – b 6.8
: Install plug (1) 1122 025 2200 and tighten down to 25 Nm (18.44 lbf ft).
: Fit spark plug (2) and tighten it
VA
176RA010
1
2
down firmly – b 3.5
– Remove the exhaust casing on the muffler – b 6.1
: Half-remove the screws (arrows) on the muffler.
VA
175RA004
: Slide the sealing plate (1) 0000 855 8106 between the heat shield and cylinder exhaust port, then tighten down the muffler screws again.
The sealing plate must completely fill the space between the two
VA
176RA012
1
screws.
– Remove the carburetor – b 12.2.1
– Set the piston to top dead center. This can be checked through the inlet port.
: Ensure that the sleeve (1) and washer (2) are fitted.
VA
176RA062
2
1
Ensure that the pin (1) is located in hole No. 1 of the test flange 1128 850 4200. If not, it must be screwed in.
VA
176RA017
1
: Slide the test flange (1) into place.
The pin must engage properly in the impulse hose (2) when positioning the test flange.
: Fit the sleeves (3)
VA 176RA013
3
4
1
2
0000 963 1008.: Fit nuts (4) and tighten them down firmly.
– Remove the carburetor and prepare for testing – b 6.2.1. : Connect pressure hose of tester
1106 850 2905 to nipple (arrow) on test flange.
VA
176RA014
: Close vent screw (1) on the rubber bulb.
VA
146RA063
1
: Pump air into the crankcase with rubber bulb until the gauge (arrow) indicates a pressure of 0.5 bar (7.25 psi). If this pressure remains constant for at least 20 seconds, the crankcase is airtight.
VA
176RA015
– However, if the pressure drops, the leak must be located and the faulty part replaced.
To find the leak, coat the suspect area with oil and pressurize the crankcase. Bubbles will appear if a leak exists.
– After finishing the test, open the vent screw and disconnect the hose of tester 1106 850 2905. – Continue with vacuum test –
b 6.2.3
Oil seals tend to fail when subjected to a vacuum, i.e. the sealing lip lifts away from the crankshaft during the piston's induction stroke because there is no internal counterpressure. An additional test can be carried out with the vacuum pump to detect this kind of fault. Carry out the same preparations as for the pressure test – b 6.2.2
: Connect suction hose of vacuum pump 0000 850 3501 to nipple (arrow) of the test flange.
VA
176RA014
: Close the vent screw (1) on the pump.
: Operate lever (2) until pressure gauge (3) indicates a vacuum of 0.5 bar (7,25 psi). VA 176RA018
3
1
2
If the vacuum reading remains constant, or rises to no more than 0.3 bar (4.35 psi) within 20 seconds, it can be assumed that the oil seals are in good condition. However, if the pressure continues to rise (reduced vacuum in the crankcase), the oil seals must be replaced, even if no leaks were detected in the pressure test.
– After finishing the test, open the vent screw and disconnect the hose.
– Remove the test flange.
– Install the carburetor – b 12.2.1 – Undo the muffler screws and
remove the sealing plate. – Take out the muffler screws in
succession and refit them with Loctite – b 16.
For further assembly of the muffler – b 6.1
– Unscrew the plug from the cylinder if necessary.
– Install the decompression valve, if fitted – b 6.8
It is not necessary to disassemble the complete crankcase to replace the oil seals.
Fan side:
– Remove the flywheel – b 7.3.1
: Remove the key (arrow).
VA
176RA019
: Take out the screws (arrows) on machines with handle heating. – Lay the generator aside.
VA
175RA031
– Free off the oil seal in its seat by tapping it with a suitable tube or a punch.
: Apply puller (1) 5910 890 4400 with No. 6 jaws 0000 893 3711. – Clamp the puller arms.
VA
176RA021
1
– Pull out the oil seal. Take care not to damage the crankshaft stub.
– The crankshaft sealing face and taper must be free from grease. Clean with standard solvent-based degreasant containing no chlorinated or halogenated hydrocarbons – b 16.
– Lubricate sealing lip of oil seal with grease – b 16.
– Thinly coat the outside of the oil seal with sealant – b 16. – Slip the oil seal, open side facing
the crankcase, over the crankshaft stub.
: Use the press sleeve (1) 1128 890 3900 to install the oil seal.
The seating face must be flat and free from burrs.
– Wait about one minute, then
VA
176RA022
1
rotate the crankshaft several times.
– Install the generator (if fitted) and tighten down the screws firmly – b 3.5
– Fit the flywheel – b 7.3.
Clutch side
– Remove the oil pump – b 11.3.1
: Remove the spacer bush (1). – Free off the oil seal in its seat by
tapping it with a suitable tube or a punch.
VA
175RA005
1
: Apply puller (1) 5910 890 4400 with No. 3.1 jaws 0000 893 3706. – Clamp the puller arms.
– Pull out the oil seal. Take care not to damage the
VA
176RA023
1
crankshaft stub.
– Cleaning sealing face with standard solvent-based degreasant containing no chlorinated or halogenated hydrocarbons – b 16.
– Lubricate sealing lip of oil seal with grease – b 16.
– Thinly coat the outside of the oil seal with sealant – b 16.
: Push the installing sleeve (1) 1122 893 4600 on to the crankshaft stub.
VA
176RA024
1
– Slip the oil seal, open side facing the crankcase, over the
crankshaft stub. : Use press sleeve (1)
1118 893 2401 to install the oil seal.
VA
176RA025
1
– Remove the installing sleeve. – Wait about one minute, then
rotate the crankshaft several times.
: Reassemble all other parts in the reverse sequence.
– Grease the outside of the spacer bush – b 16.
: Fit the spacer bush.
– Install the oil pump – b 11.3.1
VA
175RA005
– Remove the spark plug – b 5.3 : Take out the screws (arrows) on
the shroud.
– Remove the shroud. Reassemble in the reverse
VA
176RA065
sequence.
– If a decompression valve is installed, check that the cover (arrow) is correctly seated.
VA
176RA067
: Position the shroud, ensuring that the ignition lead is correctly located in the notch (arrow). Reassemble all other parts in the reverse sequence.
VA
176RA068
Before removing the piston, decide whether or not the crankshaft has to be removed as well. The crankshaft has to blocked to remove the flywheel and clutch by resting the piston on the wooden assembly block with the cylinder removed or loosened.
– Remove the muffler – b 6.1 – Remove the spark plug – b 5.3 – Remove the shroud – b 6.4 – Remove the carburetor – b
12.2.1
: Remove the cover (1) if fitted and unscrew the decompression valve (2).
VA
176RA072
2 1
: Take the sleeve (1) out of the manifold.
: Remove the washer (2) from the stud bolts.
VA
176RA261
1
2
6.4 Removing the shroud 6.5 Cylinder and Piston 6.5.1 Removing
: Unscrew the cylinder base screws through the holes (arrows) in the cylinder.
VA
176RA069
: Carefully lift the cylinder and, at the same time, push the manifold through the tank housing opening.
Do not use pointed or sharp-edged tools for this job.
VA
176RA070
: Carefully remove the cylinder gasket from the cylinder base. – Pull the cylinder off the piston. – Remove the cylinder gasket.
VA
176RA071
: Open the hose clamp (1). : Pull the manifold (2) off the intake
stub.
– Inspect the cylinder for damage and scores and replace if necessary.
VA
176RA073
2
1
– If a new cylinder has to be installed, always fit a new matching piston.
– Before removing the piston, decide whether or not the crankshaft has to be removed as well. The crankshaft has to blocked to remove the flywheel and clutch by resting the piston on the wooden assembly block with the cylinder removed or loosened.
– Remove the clutch – b 5.3 – Remove the flywheel – b 7.3
: Remove the hookless snap rings from the piston.
Wear safety glasses to protect your eyes when working with snap rings!
VA
176RA074
: Use the assembly drift (2) 1111 893 4700 to push the piston pin (1) out of the piston.
If the piston pin is stuck, tap the end of the drift lightly with a hammer if necessary.
Hold the piston steady during this
VA
176RA075
2
1
process to ensure that no jolts are transmitted to the connecting rod. – Remove the piston from the
connecting rod and take the needle cage out of the small end. – Inspect the piston rings and
: Thoroughly clean the gasket seating surface (1).
: Lubricate the needle cage (2) with oil and fit it in the small end.
2
1
VA
176RA076
– Note the installed position of the piston:
1 = Mark 2 = Flywheel
: Heat the piston to approx. 60 °C (140 °F) on a hotplate, then slide it over the connecting rod.
VA
176RA077
1
2
: Push the assembly drift 1110 893 4700, small diameter first, through the piston and small end (needle cage) and line up the piston.
VA
176RA078
: Fit the piston pin (1) on the assembly drift (2) and slide it into the piston.
VA
176RA079
1
2
: Remove the sleeve from installing tool 5910 890 2212.
VA
249RA144
: Attach the snap ring (1) to the magnet (2) so that the snap ring gap is on the flat side of the tool's shank.
VA
249RA145
2
1
: Push the large slotted diameter of the sleeve over the magnet and snap ring. Position the sleeve so that the inner pin (1) points toward the flat face (2) of tool's shank.
VA
249RA146
2
1
: Stand the installing tool, sleeve downward, on a flat surface (wooden board) and press vertically downwards until the sleeve butts against the tool's shoulder.
VA
249RA147
: Remove the sleeve and slip it onto the other end of the shank. Inner pin must again point toward flat face.
VA
249RA148
: Apply the installing tool (5910 890 2212) to the piston boss, hold the piston steady, center the tool shank exactly and press home until the snap ring slips into the groove.
VA
249RA149
Fit the snap rings so that their gaps are on the piston's vertical axis (they must point either up or down – see arrow).
VA
249RA150
: Fit new cylinder gasket, curvature facing down, on the crankcase.
VA
176RA080
: Coat the piston and piston rings with oil, then place the piston (1) on the wooden assembly block (2) 1108 893 4800.
VA
176RA081
2
1
: Align the piston rings: the bevelled radii at the join must engage the fixing pin in the ring groove.
VA
176RA082
: Push the manifold onto the intake port.
: Note the installed position (arrow).
VA
176RA083
: Fit the hose clamp (1) with the screw head on the right.
: Tighten down the clamp so that it closes against the spacer sleeve.
VA
176RA084
On clamps with spacer sleeve, tighten the screw until the gap between the two ends of the clamp is 5 to 6 mm (0.17 to 0,24 in).
: Use the clamping strap (1) 0000 893 2600 to compress the rings around the piston.
– Check correct installed position of rings once again.
– Lubricate the inside of the
VA
1
176RA086
cylinder with oil and position it in accordance with its subsequent installed position
- ensure it does not break.
: Carefully slide the cylinder over the piston, the clamping strap moves downwards at the same time.
– Remove the clamping strap and wooden assembly block.
VA
176RA087
: To pull the manifold flange through the intake opening in the tank housing, wind a piece of string (1) (about 15 cm
(5.90 in) long) around the back of the flange and pass the ends of the string through the intake opening.
VA
176RA088
1
: Press the manifold down.
: Pull the ends of the string outward.
The manifold flange is pulled through the tank housing intake opening without damaging the manifold.
VA
176RA089
– Check that flange is properly seated in the tank housing.
: Press the sleeve (1) into the manifold.
: Fit the washer (2) on the stud bolts.
VA
176RA066
1
2
– Line up the cylinder and cylinder gasket.
: Fit the cylinder base screws and tighten them down in an alternate pattern – b 3.5
VA
176RA090
: Screw home the decompression valve (2) if fitted and tighten it down firmly – b 3.5
: Fit the cover (1).
Reassemble all other parts in the reverse sequence.
VA
176RA085
1
2
– Remove the piston – b 6.5.1 – Remove rings from piston.
: Use a piece of old piston ring to scrape the grooves clean.
VA
176RA091
: Install the new piston rings in the grooves so that the radii at the ends of the rings (arrows) face upward.
– Install the piston – b 6.5.2
VA
176RA092
– Remove the chain catcher – b 5.2
– Remove the brake band – b 5.4.2
– Remove the flywheel – b 7.3 – Remove the cylinder – b 6.5.1 – Drain the oil tank.
– Drain the fuel tank.
Dispose of fuels and lubricants properly in accordance with environmental requirements.
: Pull the worm with drive spring (arrow) out of the oil pump and off the crankshaft stub.
VA
175RA025
: Take out the screws (arrows). – Remove the oil pump (1).
VA
175RA024
1
6.6 Piston Rings 6.7 Crankcase
– Remove the piston – b 6.5.2 – Remove the ignition module –
b 7.1.2
– Remove the oil seals – b 6.3 – Remove the generator on
machines with handle heating – b 14.5
: Press the grommet out of the housing.
– Pull the short-circuit wire and ground wire out of the housing.
VA
176RA101
: Unplug the impulse hose from the connector (arrow).
– Remove the screws from the annular buffers on the clutch side – b 12.8
VA
176RA102
– Remove the screw from the bottom annular buffer on the fan side – b 12.8
– Remove the crankcase from the tank housing.
– Remove the oil seals – b 6.3
: Take out the screw (arrow), steadying the self-locking nut at the same time.
– Remove the spiked bumper.
VA
176RA103
: Remove the screws (arrows) from the two halves of the crankcase.
– Draw the reflector foil off the crankcase.
VA
176RA104
: Drive the straight pin (1) on the chain tensioner side out of the two crankcase halves with a size 5 mm (1.97 in) drift (2).
VA
176RA106
1
2
– Back off the spindle (1) in service tool AS 5910 007 2205 all the way.
: Slip service tool AS (2) over the two collar studs.
: Fit the hex nuts (3) (for sprocket
VA
176RA107
2
3
1
cover) and tighten them down by hand.
: Turn the spindle (1) of the service tool clockwise until the crankshaft is pressed out of the ball bearing. The two halves of the crankcase separate during this process. – Remove the service tool AS.
: Remove the gasket from the crankcase.
VA
176RA108
– Unscrew the spindle of service tool ZS (1) 5910 007 2220 (1) a little (left-hand thread)
Make sure the retaining ring at the clutch side has been removed – b 6.3
VA
176RA332
1
2
: Position the service tool ZS (1) 5910 007 2220 against the starter side so that the
number 12 (2) on the plate is at the bottom.
The cylinder flange faces up. : Fit three M5x72 screws (arrows)
in the holes marked "12" and tighten them down against the drilled plate.
: Turn spindle (1)
counter-clockwise until the crankshaft. is pushed out of the ball bearing.
VA
176RA110
1
The crankshaft (1), connecting rod (2) and needle bearing form an inseparable unit. It must always be replaced as a complete unit. When fitting a replacement crankshaft, always install new oil seals and ball bearings.
VA
176RA111
1
2
: Drive out the deep groove ball bearing on the flywheel side with press arbor (1) 1120 893 7200.
VA
176RA112
1
: Drive out the deep groove ball bearing on the clutch side with press arbor (1) 1118 893 7200. – Inspect both halves of the
crankcase for cracks and replace if necessary.
VA
176RA113
1
The complete crankcase must be replaced, even if only one half is defective.
Check the condition of all other parts, replace if necessary and transfer to the new crankcase. If only the ball bearings are replaced, all rubber and polymer components, such as the intake hose, stop buffer and annular buffer can remain in place.
If the crankcase has to be replaced, all the components still fitted must be reused.
This involves the following operations:
– Remove the intake hose with pickup body – b 12.7
– Remove the chain tensioner – b 5.5
– Unscrew the bar mounting studs – b 5.6
– Remove the chain brake – b 5.4.2
: Press the annular buffer (1) out the crankcase half on the fan side.
: Unscrew the oil tank cap (2). : Press the cord (3) out of the
mount and remove it with the tank
VA
176RA114
3
2
1
cap.
: Press the annular buffer (arrow) out of the crankcase half on the clutch side.
VA
176RA115
New crankcases are supplied with preassembled ball bearings and oil seals. It is necessary to stamp the machine’s serial number on the crankcase with 2.5 mm
(0.98 in) figure stamps.
If only the ball bearings have to be replaced, make sure that the annular / stop buffers, intake hose and oil tank cap have been removed before heating the crankcase. If the original crankcase is used again, remove all gasket residue and clean the mating surfaces thoroughly to guarantee a perfect seal.
The following additional operations are required when using a new crankcase:
– Install the chain brake – b 5.4.3 – Fit the bar mounting studs –
b 5.6
– Install the chain tensioner – b 5.5
: The straight pin (arrow) must be fitted; if not, it must be driven into the crankcase.
– Heat the fan side of the crankcase to approx. 150 °C (302 °F) around the ball bearing seat.
VA
176RA118
: Press the deep groove ball bearing (arrow) as far as possible into the crankcase by hand with the closed side facing upwards.
VA
176RA119
This operation must be carried out very quickly because the bearing absorbs heat immediately and begins to expand.
: If it is not possible to heat the clutch side of the crankcase, use press arbor (1) 1118 893 7200 to press home the ball bearing as far as stop.
VA
176RA120
1
– Let the crankcase cool.
: Press the annular buffer in so that the circumferential groove (1) engages the edge of the crankcase (2).
VA
176RA121
2
1
: Fit nipple of tank cap cord (1) in the slot (2) and pull it forwards.
VA
176RA122
2
1
The oil pump must be fitted as stop when installing the deep groove ball bearing.
– Position the oil pump (1). – Insert the screws (arrows) and
tighten them down – b 3.5
VA
175RA024
1
– Heat the area of the ball bearing on the clutch side of the
crankcase to about 150 °C (302 °F).
: Press the ball bearing as far as possible towards the oil pump by hand with the shoulder (1) on the inside.
This operation must be carried out very quickly because the bearing absorbs heat immediately and
VA
176RA124
1
begins to expand.
: If it is not possible to heat the clutch side of the crankcase, use press arbor (1) 1118 893 7200 to press home the ball bearing as far as stop.
VA
176RA125
1
: Take out the screws (arrows). : Remove the oil pump (1).
VA
175RA024
1
– Wait for crankcase to cool down. : Press the stop buffer into the
guide until the lugs are behind the edge of the housing.
VA
176RA126
: Press both annular buffers in with the tapered edge inside until the circumferential groove (1) engages the edge of the crankcase (2).
VA
176RA127
2
1
– Install the suction hose – b 12.7
: Screw spindle of service tool ZS (2) 5910 007 2200 fully home and then screw the threaded sleeve (1) 5910 893 2420 onto the spindle.
– Lubricate tapered stub of crankshaft with oil.
VA
176RA128
1
: Place tapered stub of crankshaft in the flywheel side (ball bearing) of the crankcase.
VA
176RA129
: Screw threaded sleeve (1) to thread (2) on crankshaft stub.
VA
176RA130
2
1
: Hold the spindle steady and rotate the service tool counter-clockwise until the drilled plate butts against the crankcase.
VA
176RA131
: Turn the spindle clockwise until the crankshaft locates against the ball bearing.
The connecting rod must point toward the cylinder flange while the crankshaft is being installed.
VA
176RA132
: Hold the crankshaft steady, release the spindle counter-clockwise and then unscrew the service tool, also counter-clockwise.
VA
176RA133
: Place new gasket on clutch side of crankcase.
VA
176RA134
– Lubricate straight stub of crankshaft with oil.
: Fit crankshaft stub in the ball bearing.
VA
176RA135
: To prevent the crankcase and gasket twisting, fit M5x72 screws (arrow) in two crankcase holes and tighten them down as far as stop.
– Screw the spindle (counter-clockwise, left-hand thread) fully
VA
176RA136
into the service tool AS 5910 890 2205.
: Screw threaded sleeve (1) 5910 893 2409 of service tool AS 5910 890 2205 onto the spindle as far as stop (left-hand thread).
VA
176RA137
1
– Push the threaded sleeve over the crankshaft stub.
: Hold the crankshaft steady and rotate the spindle
counterclockwise to screw the threaded sleeve onto the crankshaft stub.
VA
176RA138
– Release the crankshaft. Hold the service tool steady and continue turning the spindle until the tool locates against the guide bar mounting face.
– Fix the nuts for the sprocket cover on the bar mounting studs and screw them down finger-tight.
: Turn the spindle counterclock-wise until the crankshaft locates against the ball bearing.
– Unscrew the hex nuts.
– Unscrew the spindle clockwise and take away the service tool.
VA
176RA139145RA152
– Take out the two M5x72 screws.
: Drive the straight pin on the chain tensioner side home with a size 5 mm (1.97 in) drift.
VA
176RA140
: Fit the screws (arrows) and tighten them down firmly in an alternate pattern – b 3.5 Trim away any excess gasket material in the area of the cylinder mounting face.
VA
176RA141
– Grease the sealing lips of the oil seals – b 16.
– Thinly coat the outer
circumference of the oil seals with sealant – b 16.
– Slide the oil seal with the open side facing the crankcase over the crankshaft stub on the fan side.
: Press the oil seal home with press sleeve (1) 1128 890 3900. The surface must be level and free from burr.
VA
176RA142
: Push the assembly sleeve 1118 893 2401 (1) over the crankshaft stub on the clutch side.
VA
176RA143
1
– Slip the oil seal over the assembly sleeve with the open side facing towards the crankcase.
: Press the oil seal home with press sleeve (1) 1118 893 4602.
VA
176RA144
1
– Remove the assembly sleeve. – Turn the crankshaft several times
after approx. 1 minute.
– Clean both halves of the crankcase.
: Affix the reflector foil without creasing so that the foil is raised on the clutch side (arrow).
VA
176RA146
The following operations are required additionally when replacing the crankcase.
– Install the chain brake – b 5.4.3 – Screw in the bar mounting
studs – b 5.6
– Install the chain tensioner – b 5.5
Reassemble all other parts in the reverse sequence.
– Remove the shroud – b 6.4 : Unscrew the decompression
valve (1).
: Install in the reverse sequence (2).
VA
176RA147
2
1
Install in the reverse sequence. – Fit the decompression valve and
tighten it down firmly – b 3.5 – Insert the cover (1).
– Fit the shroud – b 6.4
Exercise extreme caution when troubleshooting or carrying out maintenance and repair work on the ignition system. The high voltages that occur can cause serious or even fatal accidents!
Troubleshooting on the ignition system should always begin at the spark plug – b 4.4
The electronic ignition system basically consists of an ignition module (1) and flywheel (2).
VA
176RA148
2
1
The ignition module accommodates all the components required to control ignition timing. There are two electrical connections on the coil body:
: High voltage output (1) for ignition lead
VA
176RA149
1
2
: Connector tag (2) for short circuit wire
Testing in the workshop is limited to a spark test. A new ignition module must be installed if no ignition spark is obtained (after checking that wiring and stop switch are in good condition).
Ignition timing is fixed and cannot be adjusted during repair work. Since there is no mechanical wear in these systems, ignition timing cannot get out of adjustment.
– Remove the shroud – b 6.4 – Remove the fan housing with
rewind starter – b 8.2
: Pull the short-circuit wire (1) off the ignition module and pry it out of the retainer (2).
VA
176RA152
1
2
: Take out the screws (arrows). – Remove the ignition module.
VA
176RA153
If the ignition lead or spark plug boot is damage, install new parts – b 7.2
– Press the lugs of the retainer outwards if necessary. : Remove the retainer. – Connect the ignition lead if
necessary before proceeding with installation – b 7.2
VA
176RA154
: On machines with handle heating, route the wire through the retainers (arrows).
VA
176RA150
– Install the ignition module. On machines with handle heating, the plug connection from the generator must be routed under the ignition module.
– Coat the screw threads with
VA
176RA153
Loctite 242 – b 16.
Fit the ground wire under the right-hand screw of the ignition module. : Tighten down the screws
moderately (arrows).
: Turn the flywheel until the two bumps (arrows) are aligned with the ignition module.
VA
175RA014
: Slide the setting gauge (1) 1111 890 6400 between the arms of the ignition module and the raised edge of the flywheel. – Press the ignition module against
the setting gauge.
VA
176RA156
1
: Tighten down the screws of the ignition module – b 3.5 – Connect the short-circuit wire. Reassemble all other parts in the reverse sequence.
Use the ZAT 4 ignition system tester 5910 850 4503 or ZAT 3 ignition system tester 5910 850 4520 to test the ignition system.
The ignition test refers only to a spark test, not to ignition timing!
Using the ZAT 4 ignition tester 5910 850 4503
– Before starting the test, install a new spark plug in the cylinder and tighten it down firmly – b 3.5 : Unplug the boot from the spark
VA
208RA053
3
2
1
plug and connect it to the input terminal (1). Push the tester's output terminal (3) onto the spark plug.
: Crank the engine quickly with the rewind starter (min. 1,000 rpm) and check spark in the tester’s window (2).
Warning!
The engine may start and accelerate during the test!
If a spark is visible, the ignition system is in order. If no spark is visible in the window (2), check the ignition system with the aid of the troubleshooting chart – b 7.6.
Using ZAT 3 ignition tester 5910 850 4520
The ZAT 3 ignition tester
5910 850 4520 must be used to test the auxiliary spark gap
– Before starting the test, screw a
VA 208RA054 ZAT 3 5910 850 4520
3
2
1
new spark plug in the cylinder and tighten it down firmly – b 3.5 : Unplug the boot from the spark
plug in the engine and connect it to the terminal (2).
: Attach the ground terminal (1) to the spark plug.
: Use adjusting knob (3) to set the spark gap to 2 mm (0.79 in).
7.1.3 Testing the ignition system
While using the ZAT 3, hold it only by the handle (4) or position it in a safe place. Keep fingers or other parts of your body at least 1 cm away from the spark window (3), high voltage connection (2), ground connection (5) and the ground terminal (1).
Warning!
High voltage – risk of electrocution. – Crank the engine quickly with the
rewind starter (min. 1,000 rpm) and check sparkover in the tester’s window (3).
Warning!
The engine may start and accelerate during the test. If a spark is visible, the ignition system is in order.
If no spark is visible in the window (3), check the ignition system with the aid of the troubleshooting chart – b 7.6.
– Remove the ignition module – b 7.1.2
: Pull the grommet (1) off the high voltage output (2).
: Unscrew the ignition lead (3) from the high-voltage output.
VA 176RA157
3
1
2
4
: Remove the grommet and insulating tube (4) from the ignition lead.
: Pull the cover off the spark plug boot.
VA
176RA158
: Use suitable pliers to pull the leg spring out of the spark plug boot. – Unhook the leg spring from the
ignition lead.
– Pull the boot off the ignition lead.
VA
176RA159
– Cut new ignition lead to a length of 150 mm (59.06 in).
– Coat the end of the ignition lead (approx. 20 mm (7.87 in) with oil. – Push the boot onto the ignition
lead.
– Pull the ignition lead out of the boot with pliers.
– Use a pointed tool to pierce the center of the ignition lead’s insulation, about 15 mm
(5.91 in) from the end of the lead.
: Pinch the hook of the leg spring into the center of the lead (arrow).
VA
176RA160
7.2 Ignition Lead / Spark Plug Boot
: Pull the ignition lead back until the leg spring locates properly inside the spark plug boot. – Fit the cover over the spark plug
boot.
VA
176RA161
: Use a pointed tool to pierce the center of the other end of the ignition lead.
– Slip the insulating tube and grommet over the ignition lead. – Pack the high voltage output with
VA
176RA162
STIHL multipurpose grease – b 16.
Do not use either graphite grease or silicone insulating paste.
– Screw the ignition lead into the ignition module.
– Push the grommet over the high voltage output.
– Install the ignition module – b 7.1.2
– Remove the fan housing with rewind starter – b 8.2
– Block the piston with the locking strip – b 5.3
: Unscrew the flywheel nut (arrow).
VA
176RA163
: Screw the puller (1)
1110 890 4500 into the flywheel. : Screw home thrust bolt until the
flywheel is released.
VA
176RA164
1
: Pull off the flywheel.
– Remove the puller from the flywheel.
VA
176RA165
There must not be any cracks or other signs of damage in the flywheel and magnet poles, otherwise the flywheel must be replaced.
7.3 Flywheel 7.3.1 Removal
– Degrease the crankshaft stub and bore of the flywheel hub with standard solvent-based
degreasant not containing any chlorinated or halogenated hydrocarbons – b 16.
: Ensure that the key (arrow) is properly seated.
– Fit the flywheel.
– Screw on the collar nut and tighten it down – b 3.5
VA
138RA101
Reassemble remaining parts in the reverse order.
– Remove the switch shaft – b 10.1
– Turn the switch housing until the slide control is clear.
: Pull out the slide control (1) and compression spring (2).
VA
176RA166
2
1
: Carefully push the switch housing aside and remove it. – When fitting the slide control,
push it inwards until it clicks into place.
VA
176RA167
– Remove the ignition module – b 7.1
: On machines with handle heating, pull the male
connector (1) out of the female connector (2).
VA
176RA168
1
2
: Pull the wiring sideways out of the tank housing
– Remove the carburetor – b 12.2.1
VA
176RA170
: Remove the grommet and wiring from the tank housing.
VA
176RA171
