Stihl 4141 Series User manual

1Series 4141 Powerhead
© 2000 Andreas Stihl AG & Co., Waiblingen
1 Introduction 2
2 Safety Precautions 3
3 Specifications 4
3.1 Engine 4
3.2 Ignition System 4
3.3 Fuel System 4
3.4 Tightening Torques 5
4Cutch 7
4.1 Removing 7
4.2 Installing 8
4.3 Replacing the
Clutch Drum 8
4.3.1 Replacing Bearings 9
4.4 Clutch Spring 10
5Engine 10
5.1 Removing Shroud 10
5.2 Exhaust Muffler/Spark
Arresting Screen 11
5.3 Leakage Test 12
5.3.1 Pressure Test 12
5.3.2 Vacuum Test 13
5.4 Replacing the Oil
Seals 14
5.5 Replacing/Sealing
Components of Mixture
Supply System 16
5.6 Cylinder and Piston 17
5.6.1 Removing 17
5.6.2 Installing 18
5.7 Piston Rings 20
5.8 Crankcase 20
5.8.1 Removing the
Crankshaft 20
5.8.2 Replacing the Main
Bearings 21
5.8.3 Installing the
Crankshaft 23
6 Ignition System 24
6.1 Spark Plug Boot 24
6.2 Ignition Module 25
6.2.1 Ignition Timing 25
6.2.2 Removing and
Installing 26
6.3 Flywheel 26
7 Rewind Starter 27
7.1 General 27
7.2 Removing and
Installing the Rewind
Starter 28
7.3 Starter Cup 28
7.4 Rewind Spring 28
7.4.1 Replacing 28
7.4.2 Tensioning 30
7.5 Starter Rope 30
8 Throttle Control 31
8.1 Throttle Trigger/
Interlock Lever 31
8.2 Replacing the
Throttle Cable 32
8.3 Adjusting the
Throttle Cable 32
9 Fuel System 33
9.1 Air Filter 33
9.2 Carburetor 34
9.2.1 Leakage Test 34
9.3 Removing and
Installing the
Carburetor 35
9.4 Servicing the
Carburetor 35
9.5 Adjusting the
Carburetor 37
9.6 Tank Vent 38
9.7 Pickup Body 38
9.8 Fuel Tank/Fuel Hoses 39
9.8.1 Fuel Tank 39
9.8.2 Fuel Hoses 39
10 Special Servicing
Tools 40
11 Servicing Aids 41
12 Special Accessories 41
CONTENTS

2Series 4141 Powerhead
This service manual contains
detailed descriptions of all repair
andservicingproceduresspecificto
this powerhead.
There are separate handbooks for
servicing procedures on
standardized parts and assemblies
that are installed in several STIHL
power tool models. Reference is
made to these handbooks in the
appropriate chapters of this
manuals.
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 or any replacement parts.
Parts lists on microfiche and CD-
ROM are always more up to date
than printed lists.
A fault on the machine may have
several causes. To help locate the
fault, consult the troubleshooting
charts for all assemblies in the
"Standard Repairs, Trouble-
shooting" handbook.
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 a
revised edition is issued.
The special servicing tools
mentioned 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.
Symbolsareincludedinthetextand
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 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)
59108903100 with theaidof clamp
(1) 5910 890 8800. Remove the
shroud and muffler first.
The powerhead can then be
swivelled to the best position for the
VA
232RA001
2
1
ongoing repair. This leaves both
hands free.
Always use original STIHL
replacement parts.
They can be identified by the STIHL
part number, the logo
and the STIHL parts symbol .
This symbol may appear alone on
small parts.
1 Introduction

3Series 4141 Powerhead
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 owner’s manual.
Gasoline isan extremely flammable
fuel and can be explosive in certain
conditions.
Improper handling may result in
burns or other serious injuries.
Warning!
Do not smoke or bring any fire,
flame or other source of heat near
the fuel. All work with fuel must be
performed outdoors only. Spilled
fuel must be wiped away
immediately.
2 Safety Precautions

4Series 4141 Powerhead
3 Specifications
3.1 Engine STIHL single cylinder two-stroke engine
Displacement:
Bore:
Stroke:
Engine power to ISO 8893:
at 9,250 rpm
Max. permissible engine speed
without cutting tool
- without cut-off
- with cut-off in ignition module
Idle speed:
Bearings:
Piston pin diameter:
Clutch:
Clutch engages at:
Crankcase leakage test
at gauge pressure:
under vacuum:
25.4 cm3(1.55 cu.in)
34 mm (1.34 in)
28 mm (1.10 in)
0.9 kW (1.2 bhp)
12,900 ± 800 rpm
10,500 ± 500 rpm
3,000 rpm
Crankshaft supported inheavy-duty
deep-groove ball bearings, needle
cages on small and big ends
8 mm (0.315 in)
Centrifugal clutch with linings
4,100 ± 200 rpm
0.5 bar (7.25 psi)
0.5 bar (7.25 psi)
3.2 Ignition System Type:
Air gap:
Spark plug:
Electrode gap:
Transistorized magneto ignition
(breakerless) with integral
trigger unit
0.25 mm (0.010 in)
NGK CMR 7A
0.5 mm (0.020 in)
3.3 Fuel System Carburetor:
Idle setting:
Carburetor leakage test:
at gauge pressure
Fuel tank capacity:
Octane number:
Fuel mixture:
Mix ratio:
Air filter
Rotary valve carburetor
Open about 6 turns
(standard setting)
0.8 bar (11.6 psi)
700 cm3(23.7 fl.oz)
min. 90 RON (USA/CAN: pump
octane min. 87 unleaded)
Regular brand-name gasoline
and brand-name two-stroke engine
oil
50:1 with STIHL two-stroke engine
oil
Foam element and prefilter (wire
mesh)

5Series 4141 Powerhead
3.4 Tightening Torques
DG and P (Plastoform) screws are used in polymer and lightmetal 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
lbf.ft Nm
Spline screw IS-M5x10 Heat shield/cylinder 3 4
Spline screw IS-M5x16 Rewind starter/crankcase 3 4
Spline screw IS-M5x30 Control handle (bike handle) 1.5 2 with washer
Plastoform screw IS-P4x16 Control handle/handle halves
(bike handle) 0.75 1
Plastoform screw IS-P4x16 Control handle/handle halves
(loop handle) 0.75 1
Spline screw IS-M5x12 Control handle clamps/drive tube
(loop handle) 2.6 3.5
Spline screw IS-M5x60 Filter housing/carburetor/spacer flange 2.6 3.5
Spline screw IS-DG5x24 Gear housing/drive tube 6.6 9
Spline screw IS-M5x16 Shroud/rewind starter/crankcase 3 4
Spline screw IS-M5x16 Shroud/clutch housing/crankcase 3 4
Spline screw IS-M5x8 Sleeve (setscrew) 3 4
Spline screw IS-M5x30 Sleeve (tube clamp) 4.4 6
Spline screw IS-M6x35 Clamp molding/clamp (bike handle) 3.3 4.5
Collar screw M6x22 Clutch/flywheel 7.5 10 with washer
Spline screw IS-M5x16 Clutch housing/crankcase 4.4 6
Spline screw IS-M5x30 Crankcase 7.5 10
Spline screw IS-M5x25 Clampi/loop handle (loop handle) 3.3 4.5
Spline screw IS-M4x8 Diaphragm carrier 2.6 3.5
Plastoform screw P3.5x10.6 Detent spring/slide control
(control handle) 0.8 1.1
Spline screw IS-M5x50 Muffler/cylinder 5.9 8
Spline screw IS-M5x10 Guard/crankcase 3 4
Nut M8x1 Flywheel/crankshaft 14 19
M8 Starter cup/crankshaft 14 19
Spline screw IS-M3x8 Guard plate/diaphragm carrier 1.1 1.5 micro-
encapsulated
Spline screw IS-M5x16 Tank housing/crankcase 4.4 6
Spline screw IS-M5x20 Spacer flange/cylinder 4.4 6
Spline screw IS-M5x22 Cylinder/crankcase 6.6 9
M10x1 Spark plug 11 15
Spline screw IS-M4x16 Ignition module/cylinder 3.7 5

6Series 4141 Powerhead
Use the following procedure when refitting a DG or P screw in an existing thread:
–Place the 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
and weaken the assembly.
Note:
Power screwdriver settings for polymer:
–Plastoform screws max. 600 rpm
–DG screws max. 500 rpm

7Series 4141 Powerhead
Troubleshooting chart - see
"Standard Repairs, Trouble-
shooting" handbook.
–Remove shroud - see 5.1.
–Remove throttle and plug
connectors from the control
handle - see 8.2.
Remove screws from clutch
housing.
–Pull off the clutch housing with
drive tube and put them to one
side.
VA
380RA004
Inspect the clutch drum. There
should be no scores or signs of
excessive wear.
VA
380RA005
Important:
If there are signs of serious wear on
the inside diameter, check the
remaining wall thickness. If it is less
than about 80% of the original
thickness, fit a new clutch drum -
see 4.3.
VA
145RA006
80%
100%
!
Remove the spark plug. Fit the
locking screw (1) 4170 893 1200
in the spark plug hole. Turn the
crankshaftcounterclockwiseuntil
the piston butts against the
locking screw.
VA
380RA006
1
Take out the screws (1) and
remove the clutch. Remove the
spacer washers from between
the clutch and flywheel.
VA
380RA007
2
1
Note:
Do not disconnect clutch spring.
Check thickness of clutch linings
(2).
Lining thickness must be at least
1.5 mm / 0.06 in (new 3.0 mm /
0.12 in).
Note:
Damaged or oily linings must be
VA
380RA007
2
1
replaced.
4Cutch
4.1 Removing

8Series 4141 Powerhead
–Fit spacer washers.
Note:
Note installed position of clutch.
Arrowsonclutchshoespointtoward
clutch housing (see arrows in
illustration).
VA
380RA008
1
–Turn crankshaft clockwise until
the piston butts against the
locking screw 4170 893 1200.
Fit the clutch and tighten the
screws (1) to 10 Nm (7.5 lbf.ft).
–Remove locking screw
4170893 1200,fitsparkplugand
torque down to 15 Nm (11 lbf.ft).
Position engine against clutch
housing, making sure the pegs
(1) engage the holes (2) in the
crankcase.
VA
380RA009
2
1
Insert screws in crankcase and
tighten down to 6 Nm (4.4 lbf.ft).
–Install the shroud (check that
electrical wires are properly
routed) and fit the spark plug
boot.
VA
380RA004
–Fit throttle cable, connect
electrical wires in control handle.
–Remove clutch drum with
housing - see 4.1.
Release and remove screws.
VA
380RA066
Pull out the lower sleeve (3).
Then pull out the second sleeve
(with centering lug, (2)).
Take out the rubber grommet (1).
VA
380RA067
1
2
3
Use circlip pliers to remove the
circlip from the clutch housing.
VA
380RA068
4.2 Installing 4.3 Replacing the
Clutch Drum

9Series 4141 Powerhead
Use press sleeve (1)
1127 851 8300 to remove clutch
drum.
VA
380RA069
1
Usecirclip plierstoremove circlip
from clutch housing.
VA
380RA070
Use press arbor (1)
4119 893 7200 to remove the
clutch drum ball bearing from the
outside inwards.
Note:
Take care not to damage guide
pegs on clutch housing during
VA
380RA071
1
removal process.
Use press arbor (1)
4116 893 7205 to install the new
bearing.
–Secure bearing in position with
circlip.
VA
380RA072
1
Press home the clutch
drum (2) with assembly drift (1)
1110 893 4700.
–Install the circlip.
Reassemble in the reverse
sequence.
VA
380RA073
1
2
4.3.1 Replacing Bearings

10 Series 4141 Powerhead
–Remove shroud - see 5.1.
–Remove clutch housing and
clutch - see 4.1.
Removing the spring
Twist the clutch shoes in the
VA
380RA074
direction of the arrows. This
relaxes the spring so that it can
be unhooked and removed.
Fitting the spring
Engage spring in holes and slide
clutch shoes together in the
direction of the arrows.
VA
380RA075
Important:
Check installed position of spring.
Thearrowsontheclutchshoesface
upwards.
Install the clutch shoes and clutch
housing - see 4.2.
Remove screws (1 and 2) from
rewind starter.
VA
380RA001
2
1
Pull off the spark plug boot.
VA
380RA002
Take out screw (1) on clutch
housing.
Lift away the shroud and slip the
spark plug boot through the
shroud at the same time.
VA
380RA003
1
4.4 Clutch Spring 5 Engine
5.1 Removing Shroud

11Series 4141 Powerhead
–Remove wiring from the guide in
the shroud.
Install in the reverse sequence.
Troubleshooting chart - see
"Standard Repairs, Trouble-
shooting" handbook.
Warning!
To reduce the risk of burn injury, do
not touch hot parts of exhaust
system.
Allow exhaust system to cool down
first.
Spark arresting screen
–Remove shroud - see 5.1.
Usescrewdrivertoprystuboutof
muffler outlet. Remove the stub.
–Clean the spark arresting screen
VA
380RA010
or fit a new stub (with screen) if
necessary.
Exhaust muffler
–Remove shroud - see 5.1.
Remove screws (arrows) from
mufler (1).
Remove exhaust gasket (2) and
VA
380RA011
1
2
fit a new one.
Reassemble in the reverse
sequence.
–Tighten down muffler screws to
8 Nm (5.9 lbf.ft).
–Fit the shroud.
5.2 Exhaust Muffler/
Spark Arresting Screen

12 Series 4141 Powerhead
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 thus upset the fuel-air
mixture.
This makes adjustment of the
prescribed engine 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 carbu-
retor and crankcase tester and the
vacuum pump.
–Remove shroud - see 5.1.
–Make sure the spark plug is
properly tightened down.
–Remove the air filter and
carburetor - see 9.1 and 9.3.
–Set the piston to top dead center
(T.D.C.). This can be checked
through the intake port.
Mount test flange (1)
4141 850 4200 to spacer flange
with M5 x 40 screws (2).
VA
380RA012
2
1
Releasemufflermountingscrews
(2) and back them off half-way.
Slide the sealing plate (1)
0000 855 8106 between the
gasketandcylinderandretighten
the mounting screws moderately.
VA
380RA015
2
1
Note:
The sealing plate must completely
fill the space between the two
screws.
Connect pressure hose (2) of
tester1106 8502905 tonippleon
test flange (1).
VA
380RA014
2
1
Close the vent screw (1) on the
rubber bulb.
–Use rubber bulb to pump air into
the crankcase until the gauge
indicates a pressure of 0.5 bar
(7.25 psi). If this pressure
remains constant for at least
VA
143RA046
1
20 seconds, the crankcase is
airtight.
–If the pressure drops, the leak
must be located and the faulty
part replaced. Repeat the
pressure test in such a case.
Note:
To find the leak, coat the suspect
area with oil and pressurize the
crankcase again. Bubbles will
appear if a leak exists.
–Open the vent screw and
disconnect the hose.
–Thepressuretestmustalwaysbe
followed by a vacuum test.
5.3 Leakage Test 5.3.1 Pressure Test

13Series 4141 Powerhead
Oilseals tendto failwhen subjected
to a vacuum, i.e. the sealing lip lifts
awayfrom thecrankshaftduring the
piston’s induction stroke because
there is no internal counter-
pressure.
A test with the vacuum pump
0000 850 3501 is carried out to
detect this kind of fault.
Connect suction hose of the
vacuumpump (2)0000850 3501
to the nipple on the test flange
(1).
VA
380RA014
2
1
Close vent screw (1) on pump
cylinder.
Operate lever (2) until the gauge
(3) indicates a vacuum of 0.5 bar
(7.25 psi).
VA
232RA037
1
2
3
Note:
If the vacuum reading remains
constant, or rises to no more than
0.3bar(4.25psi)within20seconds,
it can be assumed that the oil seals
are in good condition.
However, if the pressure
continues to rise (reduced
vacuum), replace the oil seals,
impulse hoses (1) and/or the
diaphragm carriers (2) on the
right and left of the cylinder.
VA
380RA103
1 21
In order to exclude the influence
of the impulse hoses on the
leakage test, use hose (2)
4203 708 9506 to connect the
two diaphragm carriers (1)
together.Repeatthetestwiththis
setup.
VA
380RA013
1
2
If a leak is still indicated, check for
damage in the area of the cylinder/
oil seals.
If the leak no longer exists, look for
defect in the area of the diaphragm
carriers/impulse hoses.
–Checkimpulsehosesfordamage
or porosity and replace if
necessary.
–Repeat the leakage tests after
finishing repairs.
–Remove the test flange.
–Install impulse hoses, paying
attention to the markings on the
hoses:
F = flywheel side
S = starter side
–Install the carburetor and air filter.
–Loosen muffler mounting screws
and remove the sealing plate.
Tighten the screws to 8 Nm
(5.9 lbf.ft).
Reassemble in the reverse
sequence.
5.3.2 Vacuum Test

14 Series 4141 Powerhead
Note:
It is not necessary to disassemble
the complete engine to replace the
oil seals.
Flywheel side
–Remove shroud - see 5.1.
VA
380RA006
1
–Remove the complete clutch -
see 4.1.
Remove the spark plug. Fit the
locking screw (1) 4170893 1200
in the spark plug hole. Turn the
crankshaftcounterclockwiseuntil
the piston butts against the
locking screw.
Release and unscrew nut (2)
from flywheel (1).
VA
380RA017
2
1
Use clutch screws to secure
puller (1) 4112 890 4502 to
flywheel.
–Tighten down center screw to
remove the flywheel.
–Remove the Woodruff key from
VA
380RA018
1
the crankshaft stub.
Important:
Takecare notto damagecrankshaft
stub.
Apply puller (1) 5910 890 4400
with jaws 6 (2) and tension the
puller arms.
Pull out the oil seal.
VA
380RA019
2
1
Installing oil seal at flywheel side
–Inspect crankshaft running face
for scores.
–Clean sealing face in the
crankcase and lubricate lip of oil
seal with grease - see 11.
VA
380RA020
1
2
3
Fit installing sleeve(2)
1129 898 4600 over the
crankshaft.
Slip the oil seal (3) over the
crankshaft and against the
crankcase.
Important:
Note installed position: Closed side
of oil seal faces the flywheel.
Use the press sleeve (1)
4112893 2401topresshomethe
oil seal until it is flush with the
crankcase.
Important:
Clean crankshaft stub and hole in
flywheel with a standard solvent-
based degreasant containing no
chlorinated or halogenated
hydrocarbons - see 11.
–Fit Woodruff key in crankshaft,
mount the flywheel and tighten
down the nut to 19 Nm (14 lbf.ft).
–Remove the locking screw
4170 893 1200, install the spark
plug and tighten down to 15 Nm
(11 lbf.ft).
–Check air gap between magnets
on flywheel and ignition module -
see 6.2.2.
–Install the clutch - see 4.2.
5.4 Replacing the Oil Seals

15Series 4141 Powerhead
–Fit the shroud - see 5.1.
Starter side
–Remove shroud - see 5.1.
–Remove the rewind starter - see
7.2.
Remove the spark plug. Fit the
locking screw (1) 4170 893 1200
in the spark plug hole. Turn the
crankshaftcounterclockwiseuntil
the piston butts against the
locking screw.
VA
380RA006
1
Usewrench (2)41418931300 to
remove starter cup (1) from the
crankshaft.
VA
380RA021
2
1
Apply puller (1) 5910 890 4400
with jaws 6 (2) and tension the
puller arms.
Pull out the oil seal (3).
Important:
Take care not to damage the
VA
380RA022
2
3
1
crankshaft stub.
–Inspect crankshaft running face
for scores.
–Clean sealing face in the
crankcase and lubricate lip of oil
seal with grease - see 11.
Installing oil seal at starter side
Fit installing sleeve (2)
1129 898 4600 over the
crankshaft.
Slip the oil seal (3) over the
crankshaft and against the
crankcase.
VA
380RA023
1
3
2
Important:
Note installed position: Closed side
of oil seal (3) faces the rewind
starter.
Use press sleeve (1)
4119893 2400topresshomethe
oil seal (3) until it is flush with the
VA
380RA023
1
3
2
crankcase.
Remove the installing sleeve (2)
and press sleeve (1).
–Fit starter cup on the crankshaft
and tighten to 19 Nm (14 lbf.ft).
–Remove the locking screw
41708931200, fitsparkplugand
tighten down to 15 Nm (11 lbf.ft).
–Install the rewind starter - see
7.2.
–Fit the shroud - see 5.1.

16 Series 4141 Powerhead
Always check and 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 shroud - see 5.1.
–Remove the air filter - see 9.1.
–Remove throttle cable and plugs
from control handle - see 8.2.
–Removetheignitionmodule-see
6.2.2.
–Remove the carburetor - see 9.3.
Sealing the spacer flange
Remove mounting screws (3)
from spacer flange (4) lösen.
Disconnect impulse hoses (1)
from the diaphragm carriers on
the right and left of the cylinder.
VA
380RA024
2
4
3
1
Take the spacer flange off the
cylinder, fit a new gasket (2).
Checkimpulsehoses(1),replace
porous or torn hoses.
VA
380RA024
2
4
3
1
Replacing gaskets on intake
stubs
Note:
The cylinder has to be
disassembled to remove the
diaphragm carriers.
Take out the cylinder mounting
screws (2).
Raisethe cylinder (1)slightly and
slide the wooden assembly block
(3) 1108 893 4800 under the
piston.
–Lift away the cylinder.
VA
380RA025
1
2
3
Take out the screws (1) and
remove the diaphragm carrier
(2). Fit a new gasket.
VA
380RA026
1
2
Inspect diaphragm with support
plate (1) for signs of damage.
To remove the diaphragm, take
out the screw (2) on the support
plate.
VA
380RA027
1
2
Checking diaphragm function
–Check function of diaphragm by
blowing through or applying
suction to the connecting stub.
Suction: diaphragm closed
Blowing: diaphragm opens
If the diaphragm does not close
tight, install a new one.
5.5 Replacing/Sealing Components
of Mixture Supply System

17Series 4141 Powerhead
Installing Components
of Mixture Supply System
Fit diaphragm carriers on the right
and leftof the cylinder, tighten
screws to 3.5 Nm (2.6 lbf.ft).
Note:
Install a new cylinder gasket; the
word "FAN" must face upwards and
towards the flywheel.
–Refit the cylinder - see 5.6.2.
–Install the impulse hoses, paying
attention to the markings on the
hoses:
F = flywheel side
S = starter side
Install all other parts in the reverse
sequence.
Note:
Install new gaskets.
Always check and 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 shroud - see 5.1.
–Remove the muffler - see 5.2.
–Use combination wrench
4141 890 3400 to take out the
spark plug. Remove the ignition
module - see 6.2.2.
–Remove air filter, carburetor and
components of mixture supply
system - see 9.1, 9.2 and 5.5.
Take out the cylinder mounting
screws (3) and raise the cylinder
(2) slightly. Slide the wooden
assembly block (5)
1108 893 4800 under the piston.
Lift away the cylinder (2).
VA
380RA030
2
3
5 4
1
If a new cylinder has to be
installed, always fit the matching
piston. New cylinders are only
availablewithpiston.Transferthe
heat shield (1), the diaphragm
carriers(4)andignitionmoduleto
the new cylinder.
–Before removing the piston,
decide whether or not the
crankshaft has to be removed as
well. To remove the clutch and
starter cup, block the piston with
the wooden assembly block.
Disassemble thecrankcase- see
5.8.
Easethe hooklesssnap ringsout
of the grooves.
VA
380RA031
5.6 Cylinder and Piston
5.6.1 Removing

18 Series 4141 Powerhead
Use the assembly drift (2)
1108 893 4700 to pushthe piston
pin (1) out of the piston.
Note:
If the piston pin is stuck, tap the end
of the drift lightly with a hammer.
Hold the piston steady during this
VA
380RA032
1 2
process to ensure that no jolts are
transmitted to the connecting rod.
Pull the piston (1) off the
connecting rod (3), collect the
cover washers (2).
–Push needle bearing out of
connecting rod.
VA
380RA033
2
3
1
–Inspect piston rings and ring
grooves - see 5.7.
–Clean the gasket seating surface
on the crankcase so that it looks
bright.
Fit cylinder gasket (4) (the word
"FAN" faces up, arrow points to
flywheel).
VA
380RA035
32
1
4
–Set connecting rod to top dead
center.
Lubricate the needle bearing (3)
with oil and fit it in the small end.
Fit cover washers (1) on either
sideofsmallend,flatsidesfacing
outwards to piston.
Place the wooden assembly
block (2) 1108 893 4800 in
position.
–Heat the piston until it ishand hot.
Slip the piston over the
connecting rod, paying attention
to cover washers on needle
bearing.
Note installed position of piston:
Arrow on piston crown points to
exhaust port
VA
380RA036
21
5.6.2 Installing

19Series 4141 Powerhead
Use the assembly drift (2)
1108 893 4700 to center the
small end and piston. Then push
the piston pin (1) into position by
hand (the pin slides home easily
if the piston is hot).
–Fitthe snapringson therightand
left so that the ring gaps face
either up or down on the piston’s
vertical axis.
Install diaphragm carriers (2) on
the right and left of the cylinder
and tighten down to 3.5 Nm
(2.6 lbf.ft).
Note:
Install new gaskets.
VA
2
1
380RA037
Fit heat shield (1) on cylinder and
tighten mounting screws to 4 Nm
(3 lbf.ft).
Note installed position:
Cutout for ignition lead (see arrow)
is at exhaust side.
Position the piston rings (1) so
that the radii at the ring gap meet
at the fixing pin in the piston
groove - see 5.7.
Lubricate piston and piston rings
with oil and rest the piston on the
wooden assembly block (2)
VA
380RA028
2
1
1108 893 4800.
Note:
Lubricate the inside of the cylinder
with oil and line it up so that it is
positioned as it will be in the
installed condition. It is important to
observe this point as the piston
rings might otherwise break.
Use clamping strap (1)
0000 893 2600 to compress the
piston rings around the piston.
VA
380RA029
1
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.
VA
380RA029
1
–Line up the cylinder and gasket.
–Insert cylinder mounting screws
and tighten down to 9 Nm
(6.6 lbf.ft).
Assemble all other parts in the
reverse sequence.
Note:
Install new gaskets.
Set air gap between flywheel and
ignition module - see 6.2.2.