Stihl FS 120 User manual

1. Introduction 2
2. Specifications 3
2.1 Engine 3
2.2 Fuel System 3
2.3 Ignition System 4
2.4 Gearhead 4
2.5 Special Accessories 4
2.5.1 For User 4
2.5.2 For Service 4
2.6 Tightening Torques 5
3. Clutch 7
3.1 Removing and Installing 7
3.2 Clutch Carrier 8
4. Engine 9
4.1 Exhaust Muffler/
Spark Arresting Screen 9
4.2 Leakage Test 10
4.2.1 Preparations 10
4.2.2 Pressure Test 11
4.2.3 Vacuum Test 11
4.3 Oil Seals 12
4.4 Exposing the Cylinder 13
4.5 Cylinder and Piston 14
4.5.1 Removal 14
4.5.2 Installation 15
4.6 Piston Rings 17
4.7 Crankcase 17
4.7.1 Removing Crankshaft 17
4.7.2 Installing Crankshaft 20
4.8 Decompression Valve 23
5. Ignition System 23
5.1 Spark Plug Boot 23
5.2 Ignition Lead
(FS 400/450, FR 450) 24
5.3 Ignition Module 25
5.3.1 Ignition Timing 26
5.3.2 Removing and Installing
(FS 120...350, FR 350) 26
5.3.3 Removing and Installing
(FS 400/450, FR 450) 27
5.4 Flywheel 28
5.5 Short Circuit Wire 29
6. Rewind Starter 30
6.1 General 30
6.2 Rewind Spring 30
6.2.1 Replacing 30
6.2.2 Tensioning 31
6.3 Starter Rope/Starter
Grip (ElastoStart) 32
7. Throttle Control 33
7.1 Throttle Trigger/Interlock
Lever (Bike Handle) 33
7.2 Contact Springs/Detent
Spring in Control Handle
(Bike Handle) 34
7.3 Throttle Trigger/Interlock
Lever (Loop Handle) 34
7.4 Slide Control
(Loop Handle) 35
7.5 Throttle Cable 36
7.5.1 Replacing 36
7.5.2 Adjusting 37
8. Fuel System 38
8.1 Air Filter 38
8.2 Carburetor 39
8.2.1 Removing and Installing
(FS 120...350, FR 350) 39
8.2.2 Removing and Installing
(FS 400/450, FR 450) 40
8.2.3 Leakage Test 41
8.2.4 Adjusting
(three screws) 42
8.2.5 Adjusting
(one screw) 43
8.3 Tank Vent 44
8.4 Pickup Body 44
8.5 Fuel Tank/
Hoses 45
8.6 Manual
Fuel Pump 47
9. AV System 47
9.1 Repair
(FS 120/200) 47
9.2 Repair
(FS 300...450) 48
9.3 Repair
(FR 350/450) 50
10. Shaft 51
10.1 Bike Handle
(FS 120/200) 51
10.2 Bike Handle
(FS 300...450) 51
10.3 Loop Handle 52
10.4 Drive Shaft/
Flexible Liner 52
10.5 Flexible Shaft
(FR 350/450) 53
10.6 Drive Tube 54
10.7 Housing
(FR 350/450) 56
11. Cutting Tool
Drive 56
11.1 Gearhead 56
11.2 Clutch Drum 57
12. Support Frame
(FR 350/450) 58
12.1 Repair 58
13. Special Servicing
Tools and Aids 59
13.1 Special Servicing Tools 59
13.2 Servicing Aids 61
© 1997, Andreas Stihl, Waiblingen
CONTENTS
FS 120, 200, 300, 350, 400, 450, FR 350, 450 1

This service manual contains de-
tailed descriptions of all the repair
and servicing procedures specific
to this power tool series.
There are separate handbooks for
servicing procedures for stand-
ardized parts and assemblies that
are installed in several STIHL
power tool models. Reference is
made to these handbooks in the
appropriate chapters in this
manual.
As the design concept of models
FS 120, FS 200, FS 300, FS 350,
FS 400, FS 450 and FR 350, FR
450 is almost identical, the descrip-
tions and servicing procedures in
this manual generally apply to all
three models. Differences are de-
scribed in detail.
You should make use of the
illustrated parts lists while carrying
out repair work. They show the
installed positions of the individual
components and assemblies.
Refer to the latest edition of the
relevant parts list to check the part
numbers of any replacement parts
needed.
Parts lists on microfiche and CD-
ROM are always more up to date
than printed lists.
A fault on the power tool may have
several causes. Consult the
troubleshooting charts for all as-
semblies in the "Standard Repairs,
Troubleshooting" handbook.
Refer to the "Technical Informa-
tion" bulletins for engineering
changes which have been intro-
duced since publication of this
service manual. Technical informa-
tion bulletins also supplement the
parts list until a revised edition is
issued.
The special servicing tools men-
tioned in the descriptions are
listed in the last chapter of this
manual.
Use the part numbers to identify
the tools in the "STIHL Special
Tools" manual.
The manual lists all special
servicing tools currently available
from STIHL.
Symbols are included in the text
and pictures for greater clarity.
The meanings are as follows:
In the descriptions:
•= Action to be taken as
shown in the illustration
(above the text)
- = Action to be taken that
is not shown in the
illustration
(above the text)
In the illustrations:
=Pointer
= Direction of movement
Service manuals and all technical
information bulletins describing
engineering changes are intended
exclusively for the use of STIHL
servicing dealers. They must not
be passed to third parties.
Servicing and repairs are made
considerably easier if the machine
is mounted on assembly stand (2)
5910 890 3100 with the aid of
clamp (1) 5910 890 8800.
Secure the clamp to the assembly
stand with two washers and two
M8 nuts.
Servicing and repairs to the power-
head are considerably easier if it is
mounted on assembly stand (2)
5910 890 3100 with the aid of
clamping plate (1) 5910 890 2101.
First remove the clutch housing
and secure the powerhead to the
stand with two M6x20 and two
M10x25 hex. head screws.
The machine or powerhead can
then be swivelled to the best posi-
tion for the ongoing repair and this
leaves both hands free.
Always use original STIHL
replacement parts.
They can be identified by the
STIHL part number,
the STIHL
and the STIHL parts symbol (
The symbol may appear alone on
small parts.
1. INTRODUCTION
250RA228
1
2
VA
250RA227VA
2
1
2 FS 120, 200, 300, 350, 400, 450, FR 350, 450

2.1 Engine
STIHL single cylinder two-stroke engine with special impregnated cylinder bore
FS 120/300 FS 200/350 FS 400 FS 450
FR 350 FR 450
Displacement: 30.8 cm336.3 cm340.2 cm344.3 cm3
1.88 cu.in 2.21 cu.in 2.45 cu.in 2.70 cu.in
Bore: 35 mm 38 mm 40.0 mm 42.0 mm
1.38 in 1.49 in 1.57 in 1.65 in
Stroke: 32 mm 32 mm 32 mm 32 mm
1.26 in 1.26 in 1.26 in 1.26 in
Power output: 1.3 kW (1.8 bhp) 1.6 kW (2.2 bhp) 1.9 kW (2.6 bhp) 2.1 kW (2.8 bhp)
at 9,000 rpm
Max. permissible engine speed
without cutting tool
(cut-off speed): 12,500 ±1000 rpm 12,500 ±800 rpm
Idle speed: 2,800 rpm
Bearings: Crankshaft supported in heavy-duty ball bearings, needle cages on
small and big ends
Piston pin diameter: 10 mm (0.39 in)
Rewind starter: ElastoStart
Pawls: Single pawl system
Reserve pull on rope rotor: min. 1/2 turn
Starter rope: 3.0 mm (0.12 in) dia. x 800 mm (31.5 in)
Clutch: Centrifugal clutch without linings
Clutch engages at: 4,300 rpm
Crankcase leakage
test
at gauge pressure: 0.5 bar (7.25 psi)
under vacuum: 0.5 bar (7.25 psi)
2.2 Fuel System
Carburetor: Diaphragm carburetor
Standard setting on carburetors
with three adjusting screws
High speed screw H: Open approx. 1 turn
Low speed screw L: Open approx. 1 turn
Carburetor leakage test
at gauge pressure: 0.8 bar (11.6 psi)
Function of tank vent
at gauge pressure: ≤0.3 bar (4.35 psi)
under vacuum: ≤0.05 bar (0.725 psi)
Fuel tank capacity: 0.64 l (1.35 US pt) 0.68 l (1.44 US pt)
Octane rating: min. 90 RON (US/CAN; pump octane min. 87)
Fuel mixture: Regular brand name gasoline
and two-stroke engine oil
Mix ratio: 50:1 with STIHL two-stroke engine oil
25:1 with other brand name two-stroke, air-cooled engine oils
Air filter: Paper filter
2. SPECIFICATIONS
FS 120, 200, 300, 350, 400, 450, FR 350, 450 3

2.3 Ignition System Type: Electronic magneto
ignition (breakerless)
with integral trigger unit
and electronic speed
governor
Air gap: 0.2 - 0.5 mm (0.008 - 0.020 in)
Length of ignition lead: 305 mm * (12 in)*
Spark plug (suppressed): Bosch WSR 6F,
NGK BPMR 7 A or
Champion RCJ 6Y
Electrode gap: 0.5 mm (0.020 in)
Splark plug thread: M14x1.25
Length of thread: 9.5 mm (0.37 in)
2.4 Gearhead Type: Spiral-toothed
bevel gear drive
Gear ratio: 1:1.4 **
1:1.235
Bearings: Deep groove ball bearings
Lubrication: STIHL gear lubricant 0781 120 1117
(7 g / 0.25 oz)
2.5 Special Accessories
2.5.1 For User Full harness
Safety glasses
Transport guard for
metal cutting tools
STIHL gear lubricant (80 g/3 oz tube) 0781 120 1109
STIHL gear lubricant (80 g/3 oz tube) 0781 120 1117
2.5.2 For Service Carburetor parts kit 4134 007 1060
Set of gaskets
for FS 120, 200, 300, 350, FR 350 4134 007 1050
Set of gaskets
for FS 400, 450, FR 450 4128 007 1050
* FS 400/450 only
** FS 120, 200, 350 and 450
4 FS 120, 200, 300, 350, 400, 450, FR 350, 450

DG and P screws (Plastoform) are used in polymer and lightmetal components. These screws form a perma-
nent thread when they are installed for the first time. They can be removed and installed as often as necessary
without detrimentally affecting the strength of the screwed assembly, providing the specified tightening torque is
observed. For this reason it is essential to use a torque wrench.
Fastener Thread For component Torque Remarks
size Nm lbf.ft
Self-tapping screw IS-B3.5x6.5 Rewind spring/fan housing 1.5 1.1
Self-tapping screw IS-B4.2x9.5 Muffler/spark arresting screen 2.5 1.8 1) 2)
Spline screw IS-DG4x20 Ignition module/crankcase 4.5 3.3 3) 4) 5)
Spline screw IS-DG5x24 Ignition module/crankcase 6.0 4.4 1) 2)
Spline screw IS-DG5x12 AV sleeve/drive tube (fixing screw) 2.5 1.8 3)
Spline screw IS-DG5x12 Guard ring/gear housing 5.0 3.7 1) 4)
Spline screw IS-DG5x20 Fan housing/crankcase 6.0 4.4
Spline screw IS-DG5x20 Fan housing/shroud/crankcase 6.0 4.4
Spline screw IS-DG5x20 Carburetor housing/crankcase/
cylinder 6.0 4.4
Spline screw IS-DG5x20 Filter housing/ground wire/
crankcase 6.0 4.4
Spline screw IS-DG5x20 Ground wire/crankcase 6.0 4.4 1) 2)
Spline screw IS-DG5x26 Fuel tank/crankcase 6.0 4.4
Spline screw IS-DG5x24 Bracket/crankcase 6.0 4.4 1)
Spline screw IS-DG5x20 Shroud/clutch housing 6.0 4.4
Spline screw IS-DG5x26 Guard plate/fuel tank/
crankcase 6.0 4.4 1) 2)
Spline screw IS-DG5x24 Cylinder/crankcase 8.5 6.3
Spline screw IS-DG5x24 Muffler/crankcase 8.5 6.3
Spline screw IS-DG5x24 Muffler/cylinder 8.5 6.3
Spline screw IS-DG5x24 Crankcase 8.5 6.3
Spline screw IS-DG5x24 Clutch housing/crankcase 8.5 6.3 1) 2) 4) 5)
Spline screw IS-DG5x24 Clutch housing/crankcase 6.0 4.4 3)
Spline screw IS-DG6x28 Clutch housing/drive tube 12.0 8.8 1) 6)
Spline screw IS-DG5x24 Clutch housing/drive tube 8.5 6.3 4)
Spline screw IS-DG5x24 Gear housing/drive tube 8.5 6.3 2) 3) 5)
Spline screw IS-DG5x25 Gear housing/drive tube
Stage 1 1.5 1.1 1) 4)
Stage 2 7.5 5.5 1) 4)
Collar nut M5 Filter housing/carburetor housing 3.5 2.6
Collar screw M5/P6 Carburetor housing 4.0 3.0
Spline screw IS-M5x12 Clamp/control handle/
drive tube (loop handle) 2.0 1.5 3) 4)
Spline screw IS-M5x16 AV sleeve/drive tube (clamp screw) 5.5 4.0 3)
Spline screw IS-M5x12 Clamp/control handle/drive tube 2.0 1.5 2) 5)
Spline screw IS-M5x16 Clamp/drive tube (for harness) 4.5 3.3 3)
Spline screw IS-M5x30 Control handle (bike handle) 2.0 1.5 6)
2.6 Tightening Torques
FS 120, 200, 300, 350, 400, 450, FR 350, 450 5

Fastener Thread For component Torque Remarks
size Nm lbf.ft
Spline screw IS-M6x25 Clamp/loop handle 4.5 3.3 3)
Spline screw IS-M6x25 Support/drive tube 6.0 4.4 1) 4) 6)
Spline screw IS-M6x35 Clamp moldings/support block
(handle support/bike handle) 4.5 3.3 3)
M8 Carrier 24.0 17.7
Spline screw IS-M6x18 Clutch shoe/carrier 12.0 8.8
M8 Flywheel 32.0 23.6
M10 Decompression valve 14.0 10.3 1) 2) 4) 5)
M14x1.25 Spark plug 20.0 15.0
Screw plug M11x10 Gearhead 8.5 6.3
Spline screw IS-M5x14 Filter cover/filter housing 6.0 4.4 1) 2)
Plastoform screw IS-P4x16 Control handle/handle moldings 1.0 0.75
Collar screw IS-P3.5x10.6 Detent spring/slide control
(bike handle) 1.1 0.80 1) 3) 4)
Nut M12x1.5 L Cutting tool 25.0 18.5
Spline screw IS-M5x16 Cutting tool deflector/gearhead 4.3 3.2
Spline screw IS-M6x14 Spring/support plate 10.0 7.5 2) 5)
Spline screw IS-M6x25 Housing/shaft clamp screw 4.5 3.3 2) 5)
Spline screw IS-M6x14 Bearing housing/support frame 10.0 7.5 2) 5)
Spline screw IS-M10x20 Support plate/ball bearing/
support frame 20.0 15.0 2) 5)
Use the following procedure to fit a DG or P screw in an existing thread:
– Place the DG or P screw in the hole and rotate it counterclockwise until it drops down slightly.
– Tighten the screw clockwise to the specified torque.
This procedure ensures that the screw engages properly in the existing thread and does not form a new thread.
1) FS 400/450
2) FR 450
3) FS 120/200
4) FS 300/350
5) FR 350
6) with washer
Note: Power screwdriver speed settings for polymer: Plastoform screws max. 600 rpm
DG screws max. 500 rpm
6 FS 120, 200, 300, 350, 400, 450, FR 350, 450

Removal
Troubleshooting chart - see
"Standard Repairs, Trouble-
shooting" handbook.
Remove clutch housing -
see 9.1 or 11.2.
All models
•Inspect clutch drum. There
should be no scores or signs of
excessive wear.
Important: If there are signs of
serious wear on the inside
diameter, fit a new clutch drum -
see 11.2.
Remove the shroud - see 4.1.
Pull off the spark plug boot.
Unscrew the spark plug.
FS 120...350, FR 350
•Fit locking strip (1)
0000 893 5903.
FS 400/450, FR 450
•Fit locking strip (1)
4221 893 5900.
•Take out screws (1).
•Remove cover (2).
•Remove clutch shoes with
bushings.
•Take bushings out of the clutch
shoes.
•Twist the clutch shoes and
detach the springs.
Important: Clutch shoes and
springs must always be replaced
in pairs.
3. CLUTCH
3.1 Removing and Installing
250RA001
1
VA
250RA002
1
VA
250RA004
1
1
2
VA
250RA003 VA
250RA005 VA
250RA230 VA
250RA229 VA
)6)5 

Installation
•Fit clutch shoes with springs and
bushings so that the arrows point
counterclockwise.
•Fit cover in position.
•Insert screws and tighten down
to 12 Nm (8.8 lbf.ft).
Pull locking strip out of cylinder.
Fit spark plug and tighten down
to 20 Nm (15 lbf.ft).
Important: If the spark plug
comes with a separate terminal
nut, always fit the nut on the
thread and tighten it down
securely.
Fit the boot on the spark plug.
Fit the shroud - see 4.1.
Fit clutch housing -
see 9.1 or 11.2.
Remove clutch - see 3.1.
•Unscrew carrier from end of
crankshaft.
•Fit the carrier and tighten it
down to 24 Nm (17.7 lbf.ft).
Install the clutch - see 3.1.
3.2 Clutch Carrier
250RA232 VA 250RA231 VA
250RA234 VA
250RA235 VA
250RA233 VA
 )6)5

Troubleshooting chart - see
"Standard Repairs, Trouble-
shooting" handbook.
Spark arresting screen
FS 120...350, FR 350
•Pull spark arresting screen out of
the muffler.
Clean or replace spark arresting
screen if necessary.
FS 400/450, FR 450
•Take out the screw (1).
•Pull spark arresting screen (2)
out of the muffler.
Clean or replace spark arresting
screen if necessary.
Tighten down screw to 2.5 Nm
(1.8 lbf.ft).
Muffler
FS 400/450, FR 450
Remove air filter cover - see 8.1.
All models
•Remove screws from clutch
housing.
•Take out screws (1).
•Press down the decompression
valve (2).
•Remove the shroud (3).
•Take out the screws.
Lift away the muffler.
•Remove the gasket.
Reassemble in the reverse
sequence.
Use a new gasket.
Tighten down screws to 8.5 Nm
(6.3 lbf.ft).
250RA006 VA
250RA011 VA
250RA009 VA
250RA012 VA
250RA007
1 2
VA
1
250RA010
1
32
VA
4. ENGINE
4.1 Exhaust Muffler/Spark Arresting Screen
)6)5 

Defective oil seals, gaskets,
cracks in castings or a faulty seal-
ing ring between the carburetor
housing and cylinder are the
usual causes of leaks. Such faults
allow air to enter the engine and
thus upset the fuel-air mixture.
This makes adjustment of the
prescribed idle speed difficult, if
not impossible.
Moreover, the transition from idle
speed to part or full throttle is not
smooth.
The crankcase can be checked
thoroughly for leaks with the car-
buretor and crankcase tester and
the vacuum pump.
Remove the carburetor - see
8.2.1 and 8.2.2.
Set the piston to top dead center
(T.D.C.). This can be checked
through the inlet port.
Make sure the spark plug is
properly tightened down.
•Slide a new gasket over the
carburetor studs.
•Push the test flange (1)
1128 850 4200 into position.
•Fit and tighten down the nuts (2)
firmly.
Back off the muffler mounting
screws half-way.
•Slide the sealing plate (1)
0000 855 8106 between the
gasket and cylinder exhaust
port and retighten the mounting
screws moderately.
Note: The sealing plate must
completely fill the space between
the two mounting screws.
250RA013 VA
250RA014
21
2
VA
250RA015
1
VA
4.2 Leakage Test 4.2.1 Preparations
 )6)5

Carry out preparations -
see 4.2.1.
•Connect pressure hose of tester
1106 850 2905 to nipple on test
flange.
•Close the vent screw (1) on
the rubber bulb.
Use rubber bulb to pump air into
the crankcase until the gauge
indicates a pressure of 0.5 bar
(7.25 psi). If this pressure re-
mains constant for at least 20
seconds, the crankcase or de-
compression valve, if fitted, is
airtight.
•However, if the indicated press-
ure drops, the leak must be
located and the faulty part
replaced.
Note: To find the leak, coat the
suspect area with oil and
pressurize the crankcase again.
Bubbles will appear if a leak exists.
If the decompression valve is not
airtight, install a new one - see
4.8.
Repeat the pressure test.
Carry out the vacuum test - see
4.2.3.
After finishing the test, open the
vent screw and disconnect the
hose.
Remove the test flange.
Slacken off the muffler mounting
screws.
Pull out the sealing plate and
tighten down the screws to
8.5 Nm (6.3 lbf.ft).
Install carburetor - see 8.2.1 or
8.2.2.
Oil seals tend to fail when sub-
jected to a vacuum, i.e. the sealing
lip lifts away from the crankshaft
during the piston’s induction stroke
because there is no internal
counterpressure.
An additional test can be carried
out with the vacuum pump to
detect this kind of fault.
Carry out preparations -
see 4.2.1.
•Connect the suction hose of
vacuum pump 0000 850 3501
to test flange nipple.
•Close vent screw (1) on
pump cylinder.
•Operate lever (2) until the gauge
(3) indicates a vacuum of 0.5 bar
(7.25 psi).
250RA016 VA
250RA017 VA
143RA046 VA
1
250RA016 VA
2
50RA018
1
2
3
VA
4.2.2 Pressure Test 4.2.3 Vacuum Test
)6)5 

Note: If the vacuum reading
remains constant, or rises to no
more than 0.3 bar (4.25 psi) within
20 seconds, it can be assumed
that the oil seals are in good
condition.
However, if the pressure continues
to rise (reduced vacuum in the
crankcase), the oil seals must be
replaced.
After finishing the test, open the
vent screw and disconnect the
hose.
Remove the test flange.
Sacken off the muffler screws.
Remove the sealing plate tighten
screws to 8.5 Nm (6.3 lbf.ft).
Install carburetor - see 8.2.1 and
8.2.2.
It is not necessary to disassemble
the complete engine to replace the
oil seals.
The FS 200 engine is shown in the
illustrations.
Starter side:
Remove the flywheel - see 5.4.
Tap the oil seal with a suitable
piece of pipe or a punch to
release it from its seat.
•Apply the puller (1)
5910 890 4400 (with No. 3.1
jaws 0000 893 3706).
Tension the arms.
Pull out the oil seal.
Important: Take care not to
damage crankshaft stub.
Clean sealing surface with a
standard solvent-based degreas-
ant containing no chlorinated or
halogenated hydrocarbons - see
13.2.
Lubricate sealing lips of oil seal
with grease - see 13.2.
Slide the oil seal, open side
facing the crankcase, over the
end of the crankshaft.
•Use the press sleeve (1)
4112 893 2401 to press it fully
home.
Install flywheel - see 5.4.
Clutch side:
Remove carrier - see 3.2.
Tap the oil seal with a suitable
piece of pipe or a punch to
release it from its seat.
•Apply the puller (1)
5910 890 4400 (with No. 3.1
jaws 0000 893 3706).
Tension the arms.
Pull out the oil seal.
Important: Take care not to dam-
age crankshaft stub.
Clean sealing surface with a
standard solvent-based degreas-
ant containing no chlorinated or
halogenated hydrocarbons - see
13.2.
Lubricate sealing lips of oil seal
with grease - see 13.2.
250RA019
1
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4.3 Oil Seals
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•Slip installing sleeve (1) 4112
893 2400 over the end of the
crankshaft.
Push the oil seal, open side
facing the crankcase, over the
installing sleeve and press it
home with the press sleeve.
•Press home with press sleeve
(1) 1118 893 2401.
Remove the installing sleeve.
Install carrier - see 3.2.
Always check and, if necessary,
repair the fuel system, carburetor,
air filter and ignition system before
looking for faults on the engine.
Troubleshooting chart - see
"Standard Repairs, Trouble-
shooting" handbook.
Remove the muffler - see 4.1.
Remove the carburetor - see
8.2.1 and 8.2.2.
•Take out screws (1).
•Pull away the carburetor housing
(2).
FS 400/450, FR 450
•Disconnect hose from fuel pump
and pull it out of the guide.
•Take out screws (1).
•Pull away the carburetor hous-
ing (2), ease grommet out of
carburetor housing and pull the
extended throttle cable out of the
housing opening.
Assemble in the reverse
sequence.
•Fit stub (1) on carburetor hous-
ing in the sealing ring (2) and
throttle cable (3) in the retainer
(4).
Tighten down screws to 6 Nm
(4.4 lbf.ft).
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4.4 Exposing the Cylinder
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FS 400/450, FR 450
•Fit throttle cable (1) and grom-
met (2) in opening in carburetor
housing.
•Insert stub (3) in the sealing
ring (4).
Secure lug of extended throttle
cable between the raised marks
and tighten down the screws
to 6 Nm (4.4 lbf.ft).
Preparations - see 4.4.
Remove clutch housing -
see 9.1 and 11.2.
Pull off the spark plug boot.
On FS 120...350, FR 350: Take
ignition lead out of the retainers
on the throttle cable holder.
Unscrew the spark plug.
Unscrew the decompression
valve, if fitted.
FS 400/450, FR 450
•Take cable retainer out of
cylinder.
All models:
Illustrations show the
FS 200 engine.
•Pull out the sealing ring.
•Release and unscrew the
four cylinder base screws.
Pull the cylinder off the piston.
Inspect the cylinder and replace
it if necessary.
If a new cylinder has to be
installed, always fit the matching
piston. New cylinders are only
available with piston.
Before removing the piston,
decide whether or not the crank-
shaft has to be removed as well.
To remove the clutch and carrier,
block the crankshaft by sliding
the wooden assembly block
between the piston and crank-
case.
Remove the cylinder gasket.
•Ease the hookless snap rings
out of the grooves in the piston
bosses.
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4.5 Cylinder and Piston
4.5.1 Removal
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•Now use the assembly drift (2)
1110 893 4700 to push the pis-
ton pin (1) out of the piston.
Note: If the piston pin is stuck, tap
the end of the drift lightly with a
hammer if necessary. Hold the
piston steady during this process
to ensure that no jolts are trans-
mitted to the connecting rod.
Remove piston and take the
needle cage out of the connect-
ing rod.
•Inspect piston rings and replace
if necessary - see 4.6.
•Thoroughly clean the gasket
seating surface (1).
•Check that adapter sleeves (2)
are in place. Fit them if necess-
ary.
•Lubricate the needle cage (3)
with oil and fit it in the connecting
rod.
•To simplify assembly, heat the
piston and slip it over the con-
necting rod.
•Installed position of piston:
1 = Marking
2 = Flywheel
•Push the assembly drift, small
diameter first, through the piston
and small end (needle cage) and
line up the piston.
•Fit the piston pin (1) on the
assembly drift (2) and slide it
into the piston (the pin slides
home easily if the piston is hot).
•Modify sleeve of installing tool
5910 890 2210 as shown in
drawing.
a = 30 degrees
b = Ø 10 mm
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4.5.2 Installation
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•Use installing tool (1)
5910 890 2208 to fit the snap
rings.
Note: For instructions on how to
use the installing tool see
"Standard Repairs, Trouble-
shooting" handbook.
•Fit new cylinder gasket on the
crankcase.
•Lubricate piston and piston rings
with oil. Rest piston (1) on
wooden assembly block (2)
1108 893 4800.
•Position the piston rings so that
the radii at the ring gap meet at
the fixing pin in the piston groove
when the rings are compressed.
•Use the clamping strap (1)
0000 893 2600 to compress the
piston rings around the piston
and check that the piston rings
are correctly positioned.
Lubricate the inside of the
cylinder with oil and line it up so
that it is positioned as it will be in
the installed condition. It is im-
portant to observe this point as
the piston rings might otherwise
break.
•Slide the cylinder over the piston
- the clamping strap is pushed
downward as the piston rings
slip into the cylinder.
Remove the clamping strap
and wooden assembly block.
Line up the cylinder and gasket.
•Use socket (1) 0812 542 2104
to tighten down cylinder base
screws to 8.5 Nm (6.3 lbf.ft).
Assemble all other parts in the
reverse sequence.
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Remove the piston - see 4.5.1.
Note: The piston must be re-
moved to make sure that no
residue can fall into the crankcase
when installing the piston rings
and cleaning their grooves.
Illustrations show piston
in model FS 200.
Remove rings from piston.
•Use a piece of old piston to
scrape the grooves clean.
•Install the new piston rings in the
grooves so that the radii (1) face
the fixing pin (2).
Install the piston - see 4.5.2.
Remove the ignition module -
see 5.3.2 and 5.3.3.
Remove the fuel tank - see 8.5.
Remove the cylinder - see 4.5.1.
All models
•Take out screw (1).
•Remove top of cable guide (2).
FS 120...350, FR 350
•Take throttle cable (1) out of
base of guide (2).
•Take short circuit wire (3) out of
base of guide and remove it from
the retainers (4).
FS 400/450, FR 450
•Remove short circuit wire from
the retainers.
•Ease the grommets out of the
housing and pull out the short
circuit wire.
All models
•Pull the base of the guide
off the housing.
Remove the carrier - see 3.2.
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4.6 Piston Rings 4.7 Crankcase
4.7.1 Removing Crankshaft
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Remove the flywheel - see 5.4.
Remove the piston - see 4.5.1.
•Take out the screws.
•Place extension (1) 4116 894
1000 on crankshaft stub at clutch
side of crankcase.
•Back off spindle (left-hand
thread) of ZS installing tool (1)
5910 890 2220 a little.
•Hold ZS installing tool against
clutch side of crankcase so that
the notch marked "16" is at the
bottom.
•Insert M6x20 screws (2) in holes
marked "17" and tighten them
down against the drilled plate.
Note: ZS installing tools without
holes "16", "17" and "18" and
notches "16" and "17" can be
modified as shown in the
illustration.
Holes "16" and "18" are needed at
the starter side of the crankcase.
The illustration shows the under-
side of the drilled plate.
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41.25
33.85
9.7
26.85
2.25
250RA219
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33.3 38.0
33.6
20.6
32.25
22.5
41.6
25.5
33.7
20.1
17.65 12.6
24.75
17
19.9
18
16
18
16 16
17
18
16
18
17
16
1
2.5
15.5
16 + 18 = 5,5
17 = 6,5
VA
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•Rotate spindle (1) counterclock-
wise until the crankshaft comes
out of the ball bearing. The two
halves of the crankcase are
separated in this process.
•Puller (1) 4119 890 4600 can be
used in place of the ZS installing
tool. It is mounted to the clutch
side of the crankcase wit M6x20
screws (2).
•Turn thrust bolt (3) clockwise
until the crankshaft is released
from the ball bearing.
FS 120...350, FR 350
Back off spindle (left-hand
thread) of ZS installing tool
5910 890 2220 a little.
•Place extension (1) 4116 894
1000 on crankshat stub and
sleeve (2) 1123 851 8300 on
bores at starter side of crank-
case.
•Hold ZS installing tool (1)
5910 890 2220 against starter
side of crankcase so that the
notch marked "16" is at the
bottom.
•Insert screws (1) 9022 341 1190
(from ZS installing tool kit) in
holes marked "16", fit washers at
other side and screw on nuts.
FS 400/450, FR 450
Hold ZS installing tool against
starter side of crankcase so that
the notch marked "17" is at the
bottom.
Insert M5x60 screws in holes
marked "18", fit washers at other
side and screw on nuts.
All models
•Rotate spindle (1) counterclock-
wise until the crankshaft comes
out of the ball bearing.
•The crankshaft (1), connecting
rod (2) and needle bearing form
an inseparable unit. It must
always be replaced as a com-
plete unit.
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