Stihl 28 User manual

F
SERVICE MANUAL 028/038
FOREWORD
This Service Manual covers model
028 chain saws up to machine
number
5561640 as well as later
machines unless technical infor-
mation bulletins have been issued
in the meantime with updated
repair procedures.
Models 038 have substantially the
same constructional features as
model 028 chain saws" This Serv-
ice Manual can therefore be used
for the 038 chain saws as well.
In the event of faults it is quite pos-,
siblethat asingle malfunction may
have several causes. It is, there-
fore, advisable to consult the
"troubleshooting charts" when
tracing faults"
We also recommend
that you make use of the exploded
views in the illustrated parts lists
while carrying out repair work.
This service manual and all techni-
cal information bulletins are in-
tended exclusively for the use of
STIHL servicing staff and dealers
and must not be passed on tothird
parties.
STI H L® Andreas Stihl
Postfach 1760
Repair work is made considerably
easier if the chain saw is mounted
on assembly stand 59108503100.
The saw is easily attached to the
stand by means
of the two stud
boltsand collar nuts for barmount-
ing"
While on the assembly stand, the
chain sawcan be swivelled intoany
required position to suit the repair
in question" This not only has the
advantage of keeping the compo-
nent
in the best position for the re-
pair, but also leaves both hands
free for the work, and
thus repre-
sents a considerable time-saving.
0-7050 Waiblingen
SPECIAL TOOL
MANUAL
1
Our special tool manual illustrates
and lists the part numbers of all
available machine-related tools as
well as general purposetoolsforall
machines.
The special tool manual isavailable
in various languages and can be
ordered
by quoting theappropriate
part number listed hereunder.
German
English
French
Spanish
Yugoslav
Swedish
Italian
Portuguese
0455
901 0023
04559010123
0455 901 0223
0455
901 0323
0455
901 0423
0455901 0523
0455
901 0723
0455
901 1223

p
2
CONTENTS
1. Specifications 4 4 ..
Ignition System 26 4 .. 5 .. 1 Checking on breaker-
4.1
Construction 26 controlled ignition
45
4 .. 2 Operation 26 4.5.2 Adjustment on breaker-
2 ..
Clutch, Chain Drive 4. .2 .. 1 General information 26 controlled ignition
45
and Chain Brake 7 4.2.2
Breaker-controlled 4 .. 5 .. 3 Checking on electronic
2.1
Construction magneto ignition 27 ignition
47
and operation 7 4. .2 .. 3 Bosch transistor-controlled 4.6 Magneto edge gap
48
2 .. 1.1 Clutch and chain sprocket 7 magneto ignition 28
2
.. 1.2 Chain brake 8 4.2.4 SEM
thyristor-controlled
2.2 Troubleshooting chart 8 magneto ignition 29
2.3 Disassembly and repair 9 4
.. 2.4..1 Charging the storage 5 ..
Rewind Starter
49
2 .. 3.1 Clutch 9
capacitor
29 5
.. 1 Construction
2.3.
.2
Chain brake 12 4.2 .. 4.2Triggering the thyristor 29 and operation
49
2.4
Assembly 13 4..2.4..3 Ignition 30 5.2 Troubleshooting chart
49
2.4.1 Chain brake 13 4
.. 3 Troubleshooting chart 31 5.3 Disassembly 50
2.4.
.2
Clutch
14
4.3.1 Breaker-controlled
5.4 Replacing the starter
ignition system
31 rope
50
4 .. 3. .2
Electronic ignition 5.5 Replacing the rewind
3
.. Engine 15 system 32 spring 51
3.1 Construction 15 4.4 Function and repair 5 .. 6 Tensioning the rewind
3.2 Troubleshooting chart
15 of components 33 spring 51
3 .. 3 Exposing the cylinder
16
4.4..1 Spark plug 33 5.7 Replacing starter rope
3.4 Disassembly of cylinder 4.4..2 Ignition lead 34 guide bush 52
and piston 16 4
.. 4.3 Short-circuit wire/ground
5 .. 8 Routine maintenance 52
3.5
Assembly of piston wire 35
and
cylinder 17
4.4.4 Short-circuit contact 36
3
.. 6 Disassembly of crankcase 4.4.5 Flywheel 37
-removal
of crankshaft 19 4 .. 4.6 Armature (Bosch)/ignition 6 ..
AV Handle System 53
3.
.7 Installing the Crankshaft module (SEM) 39 6 .. 1 Construction
-
assembly of crankcase21 4.4..6 .. 1Resistance test on and operation 53
3.8 Leakage testing primary winding 39 6.
.2 Repair 53
the
crankcase 23 4.4..6.2Resistance test on
3
.. 8.1 Pressure test 23 secondary winding 39
3..8.2 Vacuum
test
25 4.4..6
.. 3Ignition coil tester
40
3.8 .. 3 Replacing the oil seals 25 4.4..6.4Disassembly 7
..
Master Control 55
and
assembly
40
7.1
Construction
4.4.7 Condenser 41
and operation 55
4.4.8 Contact
set
42 7.
.2 Disassembly
4.4..9 Trigger plate 44 and assembly 55
4
.. 5 Ignition timing 44

8"
Electric Handle Heating
System
56
8,,1
Construction
and operation
56
8.2 Troubleshooting
56
8,,3
Disassembly
and assembly
58
8.3.1 Switch
58
8,,3,,2
Heating element
in pistol grip
58
8.3.3 Handlebar
58
8,,3..4 Generator
59
9"
Chain Lubrication
60
9.1 Construction and
operation of oil pump
60
9,,2
Troubleshooting chart
61
9,,3
Oil tank/tank vent
62
9..4
Repair of pickup body
and valve
62
9.5
Disassembly and repair
of oil pump
63
1O"
Fuel System
64
1 0,,1
Construction and
operation
of carburetor
64
10"1,,1 Operation of fuel pump
64
10.1,.2 Operation of carburetor
64
10,,2
10,,3
10..4
10.5
10,,6
10,,6,,1
Troubleshooting chart
66
Leakage test
on carburetor
68
Disassembly
of carburetor
68
Repair of carburetor 69
Carburetor adjustment 71
Notes for fine adjustment
of carburetor 71
3
10.7
Fuel line and tank vent
71
10.8
Air filter and choke
72

4
1. SPECIFICATIONS
1.1
Engine
1.2 Fuel System
STIHL single cylinder, two-stroke engine with special impregnated
cylinder bore
Displacement:
Bore:.
Stroke:
Compression
ratio::
Max. torque:
Max. permissable engine speed:
Mean idle speed:
Crankshaft:
Crankshaft bearings:
Crankpin:
Big-end bearing:
Piston pin:
Small-end bearing:
Rewind starter:
Starter rope:
Clutch:
Clutch engages at:
Crankcase leakage test:
with overpressure::
with vacuu
m:
Carburetor:
Adjustment:
high-speed adjustment screw
H:
low-speed adjustment screw L:
Carburetor leakage test
with overpressure:
Fuel capacity:
47 cm3 (2 .. 87 tu. in)
44 mm (1.73 in)
31 mm (1.22 in)
9.5:1
2 .. 65 Nm (1..95 Ibf. ft) at 6000 rpm
12000 rpm
2200 rpm
Two-part, drop-forged
2 deep-groove ball bearings
14..4 mm (0.57 in) dia.
Needle cage
10 .. 0 mm (0 .. 39 in) dia.
Needle cage
Pawl engagement with automatic
starter rope rewind mechanism
3.5 mm (0 .. 14 in) dia.,
1060 mm (41.8 in) long
Centrifugal clutch without linings,
76 mm (3 in) dia.
Approx. 3100 rpm
po = 0 .. 5 bar (7 .. 1 Ibf/in2)
pu = 0.5 bar (7.1 Ibflin2)
All-position diaphragm
carburetor with integral
fuel pump
Open approx. 11/4 turns
Open approx .. 1114 turns
(basic setting with screws initially
hard against their seats)
po = 0.4 bar (5 .. 7 Ibflin2)
0.52 L (1..1 U.S.pt)

1.3 Ignition System
Fuel mixture:
Air filter::
028 AV and 028 AVQ
Type:
Magneto edge gap:
Air gap:
Ignition timing:
Ignition advance angle:
Breaker point gap::
Condenser:
Armature:
028 AVE
Type:
Air gap:
Ignition timing::
Ignition advance angle:
Armature:
028 AVEQ
Type:
Air gap:
Ignition timing:
All Models
Spark plug (suppressed):
Spark plug thread:
Fuel mix 1:40 with
STIHL two-cycle engine oil;
1:25 for other branded
two-cycle engine oils
Flat wire mesh filter
Breaker-controlled magneto
ignition system
4
.. "8 mm (0,,16 . " . 0.31 in)
0,,2 ... 0.3 mm (0.008" ". 0.012 in)
2.2
.. ,,2,,3 mm (0.087" , ,,0.091 in)
before
T..D"C.
27"".28°
5
0.35 ... 0.4 mm (0.014. ,.0.016 in)
Capacitance 0.15" ".
0.19 IlF
Coil resistors
Primary
0..7 ... 1,,00 Secondary
7..7 ... 10.3 kQ
Transistor-controlled (breaker-
less) magneto ignition system
0.2. ". 0,,3 mm (0,,008,. , 0.012 in)
2.6
mm (0,,1 in) before T.D.C"
at 8000 rpm
30° at 8000 rpm
as 028 AV/028
AVQ
Thyristor-controlled (breaker-
less) magneto ignition system
0,,2 ... 0.3 mm (0.008 ... 0,,012 in)
2.6
mm (0,,1 in) before T.D.C"
at 8000 rpm
Bosch
WSR 6 F or
Champion RCJ 6 Y
Heat range: 200
Electrode
gap:: 0.5 mm (0,,02 in)
M 14x1..25; 9.5
mm (0.37 in) long

6
1.4 Tightening Torques Crankshaft nut
(ignition side) M 8 x
1:
30 Nm (22 Ibf. ft)
Hub/spider (output side):, 50
Nm (37 Ibf. ft)
M 5 socket head screws: 8 Nm (6
Ibf.. ft)
M 5 cheese-head screws: 5 Nm
(3,,7 Ibf. ft)
M 4 cheese-head screws:, 2.5
Nm (1.8 Ibf.. ft)
M 5 nuts: 5 Nm (3.7
Ibf.. ft)
Spark plug: 25
Nm (18,,4 Ibf.. ft)
Important: The M 5 x 12 screws on the front handguard and the
M 4 x 8 screws on the spider are fitted with LOCTITE.
1.5 Cutting Attachment Guide
bars:,
STIHL Duromatic guide bars
with stellite-tipped bar nose;
STIHL Rollomatic guide bars
with sprocket nose. Both types
with corrosion resistant finish
and induction hardened track
Bar lengths: Duromatic
40 and 45 cm
(16 and 18 in)
Rollomatic 32, 37, 40 and 45 cm
(13,14.6,16 and 18 in)
Chain:, 0.325" (8,,25
mm) pitch
Chain sprocket:: 7-tooth for 0.325" chain
Chain speed:, 16.4
m/s (53.8ft/sec) at 8500 rpm
Chain lubrication:, Speed-controlled oil pump
with lift plunger, operative
only when chairi is running
Oil delivery rate: 8 cm3/min
(0,,49 cu. in/min)
at
6000 rpm
Oil tank capacity:, 0.3 L
(0,,63 U"S"pt)
1.6 Weights Model:
AV/AVE
AVQ/AVEQ
Dry weight with 32 cm
bar and chain:,
6,,5 kg (14.3 Ib)
6,,6 kg (14.5 Ib)
1,,7
Special Accessories STIHL rescue kit
028
11189005000
Gasket set 028
11180071050

2. CLUTCH,
CHAIN DRIVE AND
CHAIN BRAKE
2 .. 1 Construction and
Operation
2 .. 1 .. 1 Clutch and Chain Sprocket
The transmission of
power from the
engine to the
saw chain is effected
via a centrifugal clutch
.. O~ "Quick-
stop" models, the centrifugal clutch
incorporates an isolating clutch
which
isactuated bythechainbrake.
On the Quickstop version the hub
screwed to the crankshaft is the
clutch element which absorbs the
torque and acceleration of the
crankshaft.. It is essential that the
hub is always tightened down to the
specified torque
.. The clutch spider
is supported on the hub by a needle
sleeve and located axially with a
circlip
.. The driving plate is located
on
thethree lugs ofthe clutch spider
and can move axially while remai-
ning in
constant mesh with the
spider
.. The flat spring between the
spider and driving plate pressesthe
driving plate against the release
plate; this means
that the internal
teeth ofthe driving plate are always
in mesh with the teeth of the hub
when the chain brake is released,
and thus provides positive
trans-
mission of engine torque to the
clutch
spider .. When thechain brake
is actuated, the release plate
dis-
engages the driving plate from the
hUb .. The clutch spider and hub can
then rotate independently.
On the standard version the clutch
spider assumes the function of the
hub and must therefore always be
tightened to the specified torque
..
Chain brake engaged
The centrifugal clutch has three
clutch shoes
without linings .. The
clutch drum and chain sprocket are
separate components. The
spur
gear which drives the oil pump is a
ring-gear,
positively mountedto the
hub of the clutch drum
.. The chain
sprockethastwointegrallycastlugs
which engage in corresponding re-
cesses on the drum hub
.. As the lugs
have odd sizes, the chain sprocket
can only be fitted in one position
..
When the engine is running at idle
speed the clutch shoes are also in
the idle position, because the
ten-
sion of the clutch spring is greater
thanthecentrifugalforce .. Asengine
speed increases, centrifugal force
presses the clutch shoes outwards
against the clutch drum and thus
transmit engine torque
positively
via the chain sprocket to the saw
chain
..
The preload and strength of the
clutch spring are designed so
that
7
Chain brake released
the clutch shoes begin to make con-
tact with the clutch drum at an en-
gine speed of approx
.. 3100 rpm
(engagement speed)
.. The clutch
engagesfullyabovethisspeed
.. The
correct idle setting on the
carbure-
tor is therefore essential in order to
insure that the clutch engagement
speed is not reached when
the en-
gine is idling
..

8
2,,1,,2 Chain Brake
The chain brake is a
spring-loaded
band brake without linings" Its main
components are the brake band,
tension spring, handguard and re-
lease plate -which operates the
isolating clutch"
The chain brake is actuated by
means of the handguard which can
be used to release and engage the
brake"
2.2 Troubleshooting Chart
Fault
Saw chain turns at idle speed
The chain brake is released (reset)
by pulling the handguard back
against the handlebar"
This move-
ment is transmitted via a lever
system which preloads the tension
spring and
disengages the brake
band. At the same time the release
plate moves back and allows the
driving plate to engage in the teeth
ofthe hub"
The brake lever, which is
connected to the tension spring,
brake band and release plate, is
locked in the idle position by the
relay lever.
Cause
Engine idle speed too high
Clutch spring stretched or fatigued,
spring hooks broken
Excessive chain
sprocket wear Incorrect chain tension
Chain stops in mid-cut even with Isolating clutch worn
engine at maximum speed -
Isolating clutch disengages Flat spring broken
during cutting
Isolating clutch does not re-engage Engine idle speed too high
after releasing chain brake Flat spring broken
Saw chain does not stop imme- Tension spring broken
diately when chain brake is engaged
Thechain brake is actuated by
mo-
ving the handguard towards the bar
nose" This movementunlatches the
brake lever and causes the brake
band to be clamped around
the
clutch drum by the force of the pre-
loaded brake spring" The release
plate simultaneously
disengages
the driving plate from the hub and
interruptstheflowof powerbetween
the crankshaft and the centrifugal
clutch" Clutch drum and
saw chain
are brought to a standstill within a
fraction of a second even if the
en-
gine continues running at high
speed"
Remedy
Readjust at idle speed
adjustment
screw
Renew clutch spring
Tension saw chain properly
Renew hub and driving plate
Renew flat spring
Readjust at idle speed adjustment
screw
Renew flat spring
Renew tension spring

2,,3 Disassembly and Repair
2,,3,,1 Clutch
Top:
Chain brake released
Bottom:
Pressing out the retaining washer
First remove chain sprocket cover
and cutting attachment..
The chain brake
must be released
beforeremovingthechain
sprocket
Use a screwdriver, about 5 mm
wide, to press the retaining
washer
out of the annular groove in the
crankshaft.
The thrust washer,
chain sprocket and needle sleeve
can now be pulled off the
cranks-
haft
Top:
Removing the side plate
Center:
Releasing the cover
Bottom:
Ring-gear removed
9
Top:
Removing the spur gear
Bottom:
Clutch drum and needle sleeve removed
Remove the inner side plate - se-
cured with a single M4 x 12 cheese-
head screw" Unscrew the five
M 4 x 12
cheese-head screws and
take offthe cover" Now remove ring
gear from clutch drum hub and the
spur gear (with worm) from the oil
pump shaft by turning it clockwise.
Pull clutch drum and needle sleeve
off the crankshaft

10
Top:
Removing the circlip
Bottom:
Clutch, flat spring and needle sleeve
removed
Disassembly differs on the Quick-
stopand standardversionsfromthis
stage onwards.
On the Quickstop version, first re-
move
the circlip which locates the
clutch spider on the hub .. The clutch
with flat spring and needle sleeve
can now be pulled off the hub .. If the
hub hasto be removed, first remove
the driving plate and block the
crankshaft.. To do this, unscrew
Top:
Driving
plate removed
Center:
Locking screw 11071911200
Bottom:
Locking screw inserted
Top:
Special socket 11188931300
Bottom:
Unscrewing the hub
spark plug and fit locking screw
11071911200 in the spark plug hole
and tighten down by hand .. Use spe-
cial socket11188931300to unscrew
the hub. Remove washer from
behind hub
..

Unscrewing the clutch spider
The crankshaft must also be blo-
cked with locking screw11071911200
in
order to remove the clutch spider
on the standard version, Use' a
19 mm cranked ring wrench to un-
screwthe clutch
spider and then re-
move the dished cover plate"
Caution:Thehuband clutchspider
have left-hand threads -unscrew
them clockwise.
Wash all parts of the clutch, inclu-
ding the needle cages, in clean
gasoline and
blowout with com-
pressed
air if available" Also clean
crankshaft stub"
Always replace damaged or worn
parts,
Top:
Removing cover plate
Bottom:
Clutch spring in spring recess
Use the following procedure to re-
placetheclutch spring, clutch shoes
or spider:
First unscrew the
cover plate from
the
spider (Quickstoponly) andthen
remove the clutch shoes"
Toassembletheclutch, firstposition
theclutch spring in thespringrecess
ofoneclutch shoe, so
thatthe spring
11
Pressing clutch spring into position
hooks are in the center ofthe clutch
shoe" Nowfit the three olutch shoes
on the arms of
the spider so that the
spring recesses face away from the
triangular plate on the spider" Grip
the clutch spring with both
thumbs
and push it into the spring recesses
of the other two clutch shoes.
Refit the cover plate on the
Quick-
stop clutch" The three M 4 x 8
cheese-head screws must be secu-
red with LOCTITE"

12
2.3,,2 Chain Brake
Detaching the tension spring
The clutch drum must be removed
before the brake band can be disas-
sembled" To do this, engage the
chain brake and detach the tension
spring" Remove retaining washer
from brake
lever's pivot pin and
carefully withdraw the brake lever"
Collect the washers and helical
spring on thebrake band's pivotpin"
Theotherend ofthe brake band can
now be prised out
of its seat in the
crankcase"
Take outthe clutch before removing
the release plate" Remove the re-
taining washers, washers and heli-
cal springs from the guide pins and
take the release plate out of the
crankcase"
Unscrew the handguard (the chee-
se-head screws will be difficult to
remove becausethey are fitted with
LOCTITE) and then take out the
actuating lever, relay lever and tor-
sion spring"
Top:
Removing retaining
washer
Center and Bottom:
Unscrewing the handguard The spring guide pins in the crank-
case must be replaced if they are
damaged"
These screw pins
must be bonded
in position to prevent them loose-
ning in operation" To do this, use a
suitable solution (trichlorethlene,
diluted nitro or similar) to
complete-
lydegreasethethreads in thecrank-
case and on the pins themselves,
Then coat the threads of the screw
pinswith a little adhesive -
101, part
number 0786
111 1101, (LOCTITE
242) -and screw them into the
crankcase, Tightentoatorqueof
4,,9
Nm (0.5 kpm).
It is essential to use a suitable
screwdriver with a tip which fits
snugly in the slot of the pin in order
to avoid damaging the pin materiaL
A 1x 6.5 screwdriver in accordance
with DIN 5265 is recommended for
this purpose"

2..4 Assembly
24..1 Chain brake
Top:
Torsion
spring and relay lever in position
Bottom:
Actuating lever fitted
First fit the relay lever, actuating
lever and handguard. The ends of
the torsion spring must engage in
the hole in the crankcase and the
actuatinglever
.. The M5x12 cheese-
head screws must be secured with
LOCTITE.
Now fit release plate in crankcase
so
that its slots locate overthe guide
pins
.. Fit washer, helical spring, wa-
sher and retaining washer on the
guide pins in
that order .. Locate bent
Seat for brake band
end of brake band in its seat in the
crankcase and insert pivot pin of
brake lever in the loop of the brake
band
.. Fit washer, helical spring and
washer on the pivot pin
of the brake
lever .. Push lever onto pivot pin and
locate pin in slot of release plate at
the same time. Now secure brake
lever with retaining washer and at-
tach the tension spring using the
special assembly tool.
Top:
Brake band and brake lever in position
Center:
Special assembly tool
11178900900
Bottom:
Attaching the tension spring
13

14
2..4.2 Clutch
Top:
Tightening the hub with a torque wrench
First degrease the threads on the
crankshaft and hub (Quickstop)
or
clutch spider (standard) with a suit-
able solution (trichlorethlene, dilu-
ted nitro or similar)"
The initial assembly operations are
differenton the
Quickstop and stan-
dard versions
..
On the Quickstop version, fit the
flange washer on the crankshaft,
screw hub counter-clockwise onto
the crankshaft and tighten to a
tor-
que of 49.0 Nm (5 .. 0 kpm) using the
special socket 11188931300 and a
torque wrench"
Itisessential to observe the speci-
fied torque as the hub may other-
wise loosen during operation.
Engagethedrivingplateon theteeth
ofthe hub" The chain brake
must be
in the released condition during this
operation, Fit flat spring on lugs
of
clutch spider; the raised springtabs
Bottom:
Flat spring fitted on spider lugs
mustfaceawayfromtheclutch. Now
push clutch
together with greased
needle sleeve ontothe hub and turn
backwards and forwards until the
clutch spider lugs engage in the dri-
ving plate.. Fit circlip to secure
clutch.
On the standard version, fit cover
plate on the crankshaft so that the
raised outer
diameter faces away
from the crankcase"
Screw spider of
clutch assembly counter-clockwise
onto the crankshaft and tighten to a
torque
of 49.0 Nm (5.0 kpm) using
atorquewrenchwitha
19 mm socket.
It is essential to observethe speci-
fiedtorqueasthespidermayother-
wise loosen
in operation.
The assembly procedure is nowthe
same for both versions"
Lubricate needle sleeve of clutch
drum with antifriction grease and fit
it on the crankshaft..
Push clutch drum onto crankshaft
and needle sleeve and then fit spur
gear onto oil pump shaft. Slip ring
gear onto hub of clutch drum.
Finish
off by fitting cover and chain
sprocket; removethelocking screw,
fit and tighten down the
spark plug"

3" ENGINE
3 .. 1 Construction
Series 028 chain saws are powered
by an air-cooled, single cylinder
two-stroke engine ..
The crankcase is a two-part pres-
sure die-casting made of a special
magnesium alloy.. The two-part
drop-forgedcrankshaftissupported
in two
deep-groove ball bearings ..
Two oil seals, in thecrankcase atthe
ignition side and in the ball bearing
3.2 Troubleshooting Chart
Fault
Engine does not start easily,
stalls at idle speed, but operates
normally at full throttle
Engine does not deliver full power
or runs erratically
Engine overheating
at the other side, hermetically seal
the crank chamber.
The connecting rod, also
drop-for-
ged, is supported on needle cages
both on the crankpin and the piston
pin. Once the needle cage and the
connecting rod have been fitted, the
two halves of the crankshaft are
pressed together to form a torsio-
nally rigid assembly and then
First check fuel supply, carburetor,
air filter and ignition system before
looking for faults on the engine ..
Cause
Oil seals in crankcase
leaking
Elbow connector leaking
Crankcase damaged (cracks)
Secondary
air seepage into engine
through poorly mounted
or
faulty elbow connector
Piston rings leaking or broken
Insufficient cylinder cooling ..
Air inlet opening in fan housing
blocked or cooling fins
on cylinder plugged
15
machine finished .. For this reason a
replacement crankshaft can only
be supplied completewith connec-
ting rod and needle sleeve.
Cylinder and piston are made of a
special aluminum alloy" The cylin-
derbore is impregnated in a special
process ..
Remedy
Replace oil seals
Seal
or replace elbow connector
Replace crankshaft
Mount elbow connector correctly
or replace
Replace piston rings
Thoroughly clean all cooling air
openings

16
3,,3
Exposing the Cylinder
Top:
Removing the shroud
Bottom:
Unscrewing the muffler
First remove carburetor box cover,
unscrew spark plug and take offthe
shroud and
two-part muffler"
The cooling fins of the cylinder are
now easily accessible and can be
cleaned thoroughly" Check for da-
mage (cracks, broken cooling fins,
etc),
3.4
Disassembly of Cylinder
and Piston
Removing the cylinder base screws
Drain fuel and oil tanks, Removethe
carburetor (see 10.4) and unscrew
thefourcylinderbasescrews" Care-
fully pull the cylinder off the piston
and press the elbow connector for-
wards and ,out of the tank housing"
Before removing the piston it must
be decided
whether or not the
crankshaft is to be removed, Le. the
wooden block used to lock the
crankshaft -to facilitate removal of
the flywheel and hub (Quickstop)
or
clutch spider (standard) -must be
fitted be1ween the crankcase and
the piston"
To remove the piston, first take out
the two wire retainers and press the
piston pin out
of the piston and nee-
dle cage by means of drift
11108934700.
If the piston pin is stuck as a result
of carbonization, tap it out lightly
with a hammer and the drift. It is
Top:
Removing the wire retainers
Bottom:
Pushing out the piston pin
essential to counterhold the piston
to insurethatno joltsaretransmitted
to the connecting
rod" Remove the
piston"

3..5 Reassembly of Piston
and Cylinder
Arrow and" A" point towards exhaust
port
Ifthe cylinder hasto be replaced the
new
cylinder must always be instal-
ledwith a matching piston" Replace-
ment cylinders are only supplied
complete with piston"
If only the piston is to be renewed,
every replacement piston (marked
"B") can be used with any cylinder"
Before installing the piston, lubri-
cate the needle cage with oil and
insert it in the connec!ing
rod" Posi-
tion piston on connecting rod
sothat
thestamped markings (arrowand A)
point
towards the cylinder exhaust
port (towards tip of guide bar)" Now
fit piston pin in piston and
connec-
ting rod (needle cage)" To do this,
push
assembly drift through piston
bore and connecting rod to align
both bores concentrically" Fitpiston
pin on spigot of assembly drift and
slideintopiston" Gentlymovepiston
to and fro to ease insertion
of piston
pin,
Fitting the piston pin
The piston pin must movefreely in
its bore. Never use force during
assembly.
Insert the two wire retainers and
make sure
that they are properly
seated,
Mounting of the cylinder is best
car-
ried out using the wooden assembly
block and the ring compressor
1113 893 4900 or clamping strap
00008932600"
The elbow connector must be fitted
if a new cylinder is used"
To insure
a perfect seal, coat the inside
of the
elbow
connector's neck with sea-
ling paste 0783 810 1101" Fit elbow
connector on the intake stub so that
it faces upwards (towards
cylinder
head) and the moulding seam is
vertical (parallelwith
cylindercenter
line)" Then secure elbow connector
17
Top:
Wooden
assembly block, ring compressor
and clamping strap
Bottom:
Elbow connector in position
with hose clamp, making sure that
the clamp is correctly seated and
doesnot
distortthe elbow connector
when tightened down.

a
18
Top:
Piston on wooden assembly block
Bottom:
Piston rings correctly positioned
Fitnew cylinder gasket on the crank-
case. Lubricate piston and piston
rings with oil. Place wooden block
on the crankcase so that piston is
resting on
it..
Position each piston ring so that the
radii at
the ring gaps locate against
their respective fixing pins in the
piston grooves.
Fitting the cylinder
Insert the four M 5 x 16 socket head
screws in the cylinder mounting
holes .. Using the ring compressor or
clampingstrap, compress thepiston
rings while making sure
they are
correctly positioned.. Fit cylinder
over the piston with the exhaustport
facing in the direction of the
guide
bar tip .. During this process make
sure
that the cylinder is properly
aligned, Le. the
outer edges of the
cooling fins must be exactlyparallel
with the outeredge ofthe crankcase
atthe sprocketside .. Ifthis alignment
is not carried out, the piston rings
may break .. The ring compressor is
pushed downwards as the piston
rings move into the cylinder
.. Re-
move wooden
assembly block and
ring compressor.. Push flange of
elbow connector through the bore
in the
tank housing (do not use a
sharptool
forthis purpose)and align
the cylinder gasket and cylinder ..
Tighten down the four cylinder base
screws to a
torque of 7 .. 8 Nm
(0. .8 kpm) in a diagonal pattern..
Tightening cylinder base screws with
torque wrench
Insert sleeve in elbow connector
and then refit carburetor (see1004),
muffler, shroud, spark plug and car-
buretor box cover ..

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