Stihl 020 T User manual

STIHL 020 T 1
Service Manual
020 T Chain Saws
This manual contains detailed
descriptions of all repair and
servicing procedures for 020 T
chain saws.
You should make use of the
illustrated parts list while carrying
out repair work. It shows the
installed positions of the individual
components and assemblies.
Microfilmed parts lists are always
more up to date than printed lists.
A fault on the machine may have
several causes. Consult the
"Troubleshooting Charts" when
tracing faults.
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 re-
vised 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.
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.
Always use original STIHL
replacement parts.
They can be identified by
the STIHL part number, the
STIHl logo
and the STIHL parts symbol (
The symbol may appear alone on
small parts.
STIH
l
© 1999, Andreas Stihl AG & Co., Waiblingen
Servicing and repairs are made
considerably easier if the machine
is mounted on the assembly stand
(1). This enables the machine to be
swivelled to the best position for the
ongoing repair and leaves both hands
free.
The machine is secured to the stand
by means of the guide bar mounting
nut (after removing the sprocket
cover).

STIHL 020 T 2
CONTENTS
1. Specifications 3
1.1 Engine 3
1.2 Fuel System 3
1.3 Ignition System 4
1.4 Cutting Attachment 4
1.5 Special Accessories 4
1.5.1 For User 4
1.5.2 For Service 4
1.6 Tightening Torques 5
2. Troubleshooting
Charts 6
2.1 Clutch, Chain Drive,
Chain Brake and
Chain Tensioner 6
2.2 Engine 7
2.3 Ignition System 8
2.4 Rewind Starter 9
2.5 Chain Lubrication 9
2.6 Fuel System 10
3. Clutch, Chain Drive,
Chain Brake and
Chain Tensioner 12
3.1 Disassembling Clutch 12
3.2 Assembling Clutch 12
3.3 Chain Sprocket 13
3.4 Disassembling
Chain Brake 13
3.5 Assembling
Chain Brake 14
3.6 Chain Tensioner 15
4. Engine 16
4.1 Exhaust Muffler 16
4.2 Leakage Test 16
4.2.1 Preparations 17
4.2.2 Pressure Test 17
4.2.3 Vacuum Test 18
4.3 Oil Seals 19
4.4 Cylinder and Piston 20
4.4.1 Removal 20
4.4.2 Installation 21
4.5 Piston Rings 23
4.6 Crankcase 23
4.6.1 Removing the
Crankshaft 23
4.6.2 Installing the
Crankshaft 26
5. Ignition System 29
5.1 Spark Plug 29
5.2 Spark Plug Terminal 31
5.3 Ignition Lead 31
5.4 Ignition Module 32
5.4.1 Ignition Timing 32
5.4.2 Removing and
Installing 33
5.5 Flywheel 33
5.6 Ground Wire/
Short Circuit Wire 34
6. Rewind Starter 35
6.1 Routine Maintenance 35
6.2 Rope Rotor 35
6.3 Replacing the
Starter Rope 36
6.4 Replacing the
Rewind Spring 36
6.5 Tensioning the
Rewind Spring 37
6.6 Pawl 38
6.7 Starter Rope
Guide Bush 38
7. AV Handle System 39
8. Master Control/
Handle System 40
8.1 Master Control Lever 40
8.2 Choke/Throttle
Rods 40
8.3 Interlock Lever/
Throttle Trigger 41
8.4 Switch Shaft 41
8.5 Contact Springs 41
8.6 Double Lever
(Choke/Throttle) 42
8.7 Front Handle 42
8.8 Handle Housing 43
9. Chain Lubrication 44
9.1 Suction Hose/
Pickup Body 44
9.2 Vent Valve 45
9.3 Oil Pump 46
9.3.1 Removing and
Installing 46
9.3.2 Servicing 46
10. Fuel System 47
10.1 Air Filter 47
10.2 Carburetor 47
10.2.1 Removing and
Installing 47
10.2.2 Leakage Testing 48
10.2.3 Servicing 48
10.3 Carburetor
Adjustment 53
10.4 Pickup Body/
Fuel Hose 54
10.5 Tank Vent 55
10.6 Tank Housing 55
11. Special Servicing
Tools and Aids 57
11.1 Special Servicing
Tools 57
11.2 Servicing Aids 58

STIHL 020 T 3
1.2 Fuel System Carburetor:
Standard setting
High speed adjusting screw H:
Low speed adjusting screw L:
Carburetor leakage test
at gauge pressure:
Fuel tank capacity:
Octane number:
Fuel mixture:
Mix ratio:
Air filter:
Diaphragm carburetor
Back off approx. 1 turn
Back off approx. 1 turn
0.4 bar (5.8 psi)
0.37 I (0.8 US pt)
mind. 90 RON (USA/CAN: pump
octane min. 87 unleaded)
Regular brand-name gasoline
and two-stroke engine oil
50:1 with Stihl two-stroke
engine oil
25:1 with other brand-name
two-stroke, air-cooled
engine oils
Dual-ply synthetic fabric
or flocked wire mesh element
and foam element
35.2 cm
3
(2.15 cu.in)
40 mm (1.57 in)
28 mm (1.10 in)
7.41:1
1.6 kW (2.2 bhp)
1.8 Nm (1.3 Ib.ft)
at 7,500 r.p.m.
14,000 r.p.m.
2,800 r.p.m.
Crankshaft supported in heavy-
duty roller bearings, needle
cages on small and big ends
9 mm (0.35 in)
49 mm (1.93 in)
Pawl system
min. 1/2 turn
3.0 mm (0.12 in) dia., 800 mm
(31.5 in) long
Centrifugal clutch without linings
66 mm (2.60 in)
3,900 r.p.m.
0.5 bar (7.25 psi)
0.5 bar (7.25 psi)
STIHL single-cylinder two-stroke engine with special
impregnated cylinder bore
Displacement:
Bore:
Stroke:
Compression ratio:
Power output:
Max. torque:
Max. permissible engine
speed with bar and chain:
Mean idle speed:
Bearings:
Piston pin diameter:
Connecting rod length:
Rewind starter:
Reserve pull on rope rotor:
Starter rope:
Clutch:
Diameter:
Clutch engages at:
Crankcase leakage
test
at gauge pressure:
under vacuum:
1. SPECIFICATIONS
1.1 Engine

STIHL 020 T 4
1.3 Ignition System
1.4 Cutting Attachment
1.5 Special Accessories
1.5.1 For User
1.5.2 For Service Shop
Type:
Air gap:
Ignition timing:
Advance angle:
Spark plug (suppressed):
Electrode gap:
Spark plug thread:
Length of thread:
Heat range:
Guide bars:
Bar tail:
Bar lengths:
Oilomatic chain:
Chain sprockets:
Chain speed:
Chain lubrication:
Oil feed rate (adjustable):
Oil tank capacity:
STIHL repair kit
7-tooth 3/8" P spur sprocket
8-tooth 1/4" spur sprocket
Elastostart
Air filter (flocked)
Carburetor parts kit
Gasket kit
Spur gear/tensioning screw kit
Electronic magneto ignition
(breakerless) with integral
trigger unit
0.25 mm (0.010 in)
2.0 - 2.8 mm B.T.D.C.
at 8,000 r.p.m.
24.7 -32.5° B.T.D.C.
at 8,000 r.p.m.
Bosch WSR 6 F or NGK BPMR 7 A
0.5 mm (0.020 in)
M14x1.25
9.5 mm (0.37 in)
200
Rollomatic
3005
30, 35, 40 and 45 cm
(12, 14, 16 and 18 in)
3/8" (9.32 mm) Picco-Micro
Optional:
1/4" (6.35 mm) Rapid-Micro
6-tooth spur sprocket for 3/8" Picco
Optional:
7-tooth for 3/8" Picco
8-tooth for 1/4"
18.6 m/s (61 ft/sec) at 10,000 r.p.m.
(with 6-tooth 3/8" P sprocket)
Speed-controlled reciprocating
oil pump, no oil feed at
idle speed. Additional manual
oil flow adjustment
4.0 - 10.5 cm3/min
0.14 -0.36 fl.oz/min) at 10,000 r.p.m.
0.24 I (0.5 US pt)
1129 900 5000
1129 640 2050
1129 640 2051
1128 190 3400
1129 120 1606
1129 007 1060
1129 007 1050
1129 007 1000

STIHL 020 T 5
Torque
Nm Ibf.ft
1.7 1.25
3.2 2.4
1.6 1.2
4.0 3.0
7.0 5.2
11.5 8.5
3.2 2.4
3.5 2.6
6.0 4.4
7.0 5.2
4.0 3.0
4.0 3.0
3.2 2.4
2.4 1.8
3.0 2.2
5.5 4.0
5.3 3.9
6.5 4.8
7.0 5.2
11.5 8.5
3.3 2.5
25.0 18.5
32.5 24.0
25.0 18.5
4.0 3.0
5.5 4.0
1.7 1.25
5.5 4.0
1.3 0.95
1.6 Tightening Torques
Plastoform screws are used for polymer components and "DG" screws for 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 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
Spline screw
Spline screw
Spline screw
Spline screw
Spline screw
Spline screw
Spline screw
Spline screw
Spline screw
Spline screw
Spline screw
Spline screw
Spline screw
Spline screw
Spline screw
Spline screw
Spline screw
Spline screw
Spline screw
Spline screw
Nut
Collar nut
Collar nut
Screw assembly
Spline screw
Spline screw
Screw
Screw
Thread size
IS-P 4x14
IS-P 4x14
IS-P 4x14
IS-DG 4x15
IS-M 5x12
IS-M 5x20
IS-DG 4x15
IS-M 4x12
IS-M 5x12
IS-P 6x19
IS-P 5x20
IS-M 4x16
IS-P 4x10
IS-M 4x12
IS-M 4x12
IS-M 4x16
IS-M 4x16
IS-M 4x20
IS-M 5x12
IS-M 5x16
M 5
M 8x1
M 8x1 L
M 14x1.25
IS-P 5
IS-M 4x16
IS-P 4x14
IS-P 6x21.5
IS-P 4x10
For component
Chain catcher
Insert, chain brake
Handle molding
Muffler
Spiked bumper/crankcase
Muffler to cylinder
Insert
Oil pump
Annular buffer/front handle
Ring on housing
Fan cover/tank housing
Fan cover/crankcase
Segment/fan cover
Cover/chain tensioner
Cover/oil pump
Crankcase
Tank housing
Ignition module
Bar mounting flange/crankcase
Cylinder
Carburetor
Flywheel
Clutch
Spark plug
Annular buffer/handle housing
Annular buffer, front
Annular buffer, rear
Front handle/handle housing
Control lever/switch shaft
Remarks
1)
1)
1)
2)
1)
1)
1)
2) 3)
2)
1)
1)
1)
1)
Use the following procedure when refitting a P or DG 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.
1) Torque may be reduced by approx. 1 Nm (0.7 Ibf.ft) when refitting a screw in an existing thread
2) Screw must be secured with adhesive 0786 111 1101 (Loctite 243).
3) A washer must be fitted under the screw head.
Note: Screws secured with adhesive are easier to release if the adhesive is heated first with a hot air blower (hair dryer).
Exercise caution on polymer components.

STIHL 020 T 6
2. TROUBLESHOOTING CHARTS
2.1 Clutch, Chain Drive, Chain Brake and Chain Tensioner
Condition
Saw chain turns at idle speed
Loud noises
Chain sprocket wears rapidly
Chain wears rapidly
Chain does not stop immediately
when brake is activated
Cause
Engine speed too high
Spring hooks broken
Clutch springs stretched or
fatigued
Needle cage damaged
Clutch shoe retainer broken
Clutch shoes and carrier
worn
Chain not properly tensioned
Chain not properly tensioned
Poor chain lubrication
Worn chain sprocket
Brake spring broken
Brake band stretched or
broken
Remedy
Readjust at idle speed
adjusting screw
(counterclockwise)
Fit new springs
Replace all clutch springs
Fit new needle cage
Fit new retainer
Fit new clutch
Tension chain as specified
Tension chain as specified
Check chain lubrication and
rectify problem
Fit new sprocket
Fit new brake spring
Fit new brake band

STIHL 020 T 7
2.2 Engine
Always check and, if necessary, repair the following parts before looking for faults on the engine:
- Air filter
- Fuel system
- Carburetor
- Ignition system
Condition
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
Cause
Oil seals in crankcase
damaged
Manifold leaking
Cylinder base gasket leaking
Crankcase damaged (cracks)
Secondary air seepage through
poorly mounted or faulty manifold
Piston rings leaking or
broken
Muffler carbonized
Insufficient cylinder cooling.
Air inlets in fan housing
blocked or cooling fins on
cylinder very dirty
Remedy
Replace oil seals
Seal or replace manifold
Replace gasket
Replace crankcase
Mount manifold correctly or
replace
Fit new piston rings
Clean muffler (inlet and
exhaust), replace spark
arresting screen (if fitted)
Thoroughly clean all cooling air
openings and cylinder fins

STIHL 020 T 8
2.3 Ignition System
Warning: Exercise extreme caution while carrying out maintenance and repair work on the ignition system.
The high voltages which occur can cause serious or fatal accidents!
Ignition system in order.
Look for fault in fuel system and
carburetor.
yes
Replace ignition module. Does engine
now run after positive spark test?
Fit new flywheel.
Is spark test positive?
Use ohmmeter to check ignition lead
for break. If break is detected, replace
ignition lead. Does spark test now
produce sparkover?
Does flywheel appear to
be in good condition?
Fit new spark plug.Is air gap correct?
Adjust air gap (0.25 mm/0.010 in).
Is spark test positive?
Insert screwdriver in place of spark plug in spark plug
terminal and hold about 4 mm (1/8") away from
ground. Sparkover?
Replace faulty ignition lead of short
circuit wire. Repair contact spring.
Faulty insulation on ignition
lead or short circuit wire?
Clean spark plug and reset electrode gap.
Does spark test produce powerful spark?
Press terminal firmly onto spark
plug and fit spring if necessary.
Spark plug terminal firmly seated on spark plug?
Remove spark plug.
Is it in good condition?
no
no
no
no
no
yes
no
no yes
yes no
no
no
no
yes
yes

STIHL 020 T 9
2.4 Rewind Starter
Condition
Starter rope broken
Rewind spring broken
Starter rope can be pulled out
almost without resistance
(crankshaft does not turn)
Starter rope is difficult to pull
and rewinds very slowly
Cause
Rope pulled out too vigorously
as far as stop or over edge –
i.e. not vertically
Normal wear
Spring overtensioned –
no reserve when rope is
fully extended
Very dirty or corroded
Guide peg on pawl or pawl
itself is worn
Spring clip fatigued
Starter mechanism is very
dirty (dusty conditions)
Lubricating oil on rewind
spring becomes viscous
at very low outside tem-
peratures (spring windings
stick together)
Remedy
Fit new starter rope
Fit new starter rope
Fit new rewind spring
Fit new rewind spring
Fit new pawl
Fit new spring clip
Thoroughly clean complete
starter mechanism
Apply a few drops of kerosine
(paraffin) to spring, then pull rope
carefully several times until normal
action is restored
Remedy
Fill up with oil
Clean oil inlet hole
Wash intake hose and pickup body
(strainer) in white spirit and blow out
with compressed air; replace if
necessary
Clean or replace valve
Fit new pump piston and/or
new worm
Cause
Oil tank empty
Oil inlet hole in guide bar is
blocked
Intake hose or pickup body
(strainer) clogged or intake
hose ruptured
Valve in oil tank blocked
Teeth on pump piston and/or
worm worn
Condition
Chain receives no oil
2.5 Chain Lubrication
Important: In the event of trouble with chain lubrication system, always investigate the other possible sources of faults
before disassembling the oil pump.

STIHL 020 T 10
Condition
Machine losing chain oil
Oil pump delivers too
little oil
2.6 Fuel System
Condition
Carburetor floods;
engine stalls
Poor acceleration
Cause
Bore in pump housing
worn
Control screw and/or control
edge on pump piston worn
Bore in pump housing
Cause
Inlet needle not sealing.
Foreign matter in valve seat or
cone damaged
Inlet control lever sticking on
spindle
Helical spring not located on
nipple of inlet control lever
Perforated disc on diaphragm is
deformed and presses constantly
against inlet control lever Inlet
control lever too high (relative to
design position)
Idle jet "too lean"
Main jet "too lean"
Inlet control lever too low
(relative to design position)
Inlet needle sticking to valve
seat
Connecting bore to atmosphere
blocked
Remedy
Fit new pump housing
Fit new control screw and/or
pump piston
Fit new pump housing
worn
Remedy
Remove and clean or replace
inlet needle, clean fuel tank,
pickup body and fuel line if
necessary
Free off inlet control lever
Remove inlet control lever
and refit correctly
Fit new metering diaphragm
Set inlet control lever flush with
bottom of metering chamber
Back off low speed adjusting
screw slightly (see Carburetor
Adjustment)
Back off high speed adjusting
screw slightly (see Carburetor
Adjustment)
Set inlet control lever flush with
bottom of metering chamber
Remove inlet needle, clean and
refit
Clean bore

STIHL 020 T 11
Cause
Diaphragm gasket leaking
Metering diaphragm damaged or
shrunk
Throttle shutter opened too wide
Idle jet bores or ports
blocked
Idle jet "too rich"
Setting of idle speed
adjusting screw incorrect
- throttle shutter completely
closed
Small plastic plate in valve
jet does not close
Air filter dirty
Tank vent faulty
Leak in fuel line between tank
and fuel pump
Pump diaphragm damaged or
fatigued
Main jet bores or ports
blocked
Fuel pickup body dirty
Fuel strainers dirty
Remedy
Fit new diaphragm gasket
Fit new metering diaphragm
Reset idle speed adjusting screw
by idle speed adjusting screw
correctly
Clean jet bores and ports
with compressed air
Screw down low speed adjusting
screw slightly
(see Carburetor Adjustment)
Set idle speed adjusting
screw correctly
Clean or renew valve jet
Clean air filter
Clean or replace tank vent if
necessary
Seal or renew connections
and fuel line
Fit new pump diaphragm
Clean bores and ports
Clean pickup body, fit new
filter
Clean fuel strainers
Condition
Engine will not idle,
idle speed too high
Engine stalls at idle speed
Engine speed drops quickly under
load - low power
See also 2.2

STIHL 020 T 12
3. CLUTCH, CHAIN DRIVE, CHAIN BRAKE AND CHAIN TENSIONER
3.1 Disassembling Clutch 3.2
A
ssemblin
g
Clutch
Troubleshooting chart - see 2.1.
• Disengage the chain brake by
pulling the hand guard toward
the front handle.
• Unscrew collar nut (1) and
remove the sprocket cover.
• Unscrew the clutch from the
stub of the crankshaft.
Caution: Clutch has a left-hand
thread.
• Slip the retainers (1) onto the
clutch shoes (2) so that the
narrow side is next to the series
number, e.g. 1129 (3).
• Fit the clutch shoes over the arms
(1) of the clutch carrier so that the
series number is on the same side
as the larger hexagon (2).
• Use assembly hook (2) to remove
all the clutch springs (1).
• Pull the clutch shoes off the
carrier.
• Pull the retainers off the clutch
shoes.
• Clean all parts and stub of
crankshaft in white spirit.
Replace any damaged or worn
parts.
• Pull terminal (1) off the spark plug
(2). Unscrew the spark plug.
• Set piston to bottom dead center.
• Push the locking strip (1), thicker
end (2) first, into spark plug hole
and then rotate it 180°.
• Clamp the clutch, e.g. one shoe,
in a vise.

STIHL 020 T 13
3.3 Chain Sprocket 3.4 Disassembling
Chain Brake
• Attach one end of each spring
(1) to the clutch shoes.
• Use the assembly hook (2) to
attach the other ends of the
springs and press them firmly
into the clutch shoes with one
finger.
• Remove clutch - see 3.1.
• Pull chain sprocket off the cranks-
haft.
• Remove sprocket cover –
see 3.1.
• Engage brake band by pushing
the hand guard away from the
sprocket cover.
• Take out screws (1).
• Remove the segment (2).
• Take the needle cage out of the
sprocket.
• Clean stub of crankshaft.
Wash needle cage in clean white
spirit and lubricate with grease
- see 11.2. Replace damaged
needle cage.
• The chain sprocket must engage
the worm properly.
• Install clutch - see 3.2.
• Screw clutch onto crankshaft and
torque down to 32.5 Nm (24 Ibf.ft).
• Remove locking strip from
cylinder. Install spark plug and
torque down to 25 Nm (18.5 Ibf.ft).
Refit terminal.
• Fit sprocket cover so that pin (1)
engages hole (2).
• Fit the collar nut.
• Carefully pry the brake spring (1)
off the anchor pin and unhook it
from the bell crank (2).

STIHL 020 T 14
3.5 Assemblin
g
Chain Brake
• Take the brake band (1) out of the
sprocket cover and detach it from
the bell crank (2) at the same time.
• Fit lever with pivot pin and press it
home as far as stop.
• Slide bell crank into end of hand
guard. The long arm (1) of the
bell crank must point to the hole
(2)
• Locate the hand guard and bell
crank on the pivot pins.
• Now press the flat spring (1)
down and push the hand guard
and bell crank fully home.
• Fit flat spring (1) in position.
• Ease the hand guard (1) and bell
crank (2) off the pivot pins.
• Pull the bell crank out of the
hand guard and then take the
hand guard out of the sprocket
cover.
• Remove lever (1) with pivot pin
and flat spring (2).
• Inspect parts. Replace any worn
or damaged parts.
• Fit hand guard in the sprocket
cover.
• Attach brake band to the bell
crank.

STIHL 020 T 15
• Press the brake band into the
sprocket cover.
Important: Coat sliding and bear-
ing points of chain brake with Moly-
kote grease - see 11.2.
Do not lubricate the brake band.
• Pull the spur gear (1) out of the
cover (2).
• Remove chain sprocket cover –
see 3.1.
• Remove screw from cover.
3.6 Chain Tensione
r
• Use the assembly tool (2) to attach
the brake spring (1) to the anchor
pin.
• Fit the segment and tighten
screws to 3.2 Nm (2.4 Ibf.ft).
• Remove the thrust pad (1).
• Rotate the spur gear (2) to unscrew
the adjusting screw (3) fully from the
tensioner slide (4).
• Hook the brake spring onto the
bell crank.
• Take out the complete chain
tensioner.
• Pull off the tensioner slide (1).
• Remove the adjusting screw (2).
• Inspect the teeth on the spur gear
and adjusting screw. If the teeth are
damaged, replace both parts.
Reverse the above sequence to
install the chain tensioner.
Note: Coat teeth of adjusting
screw and spur gear with grease,
see 11.2, before refitting.

STIHL 020 T 16
4. ENGINE
4.1 Exhaust Muffle
r
4.2 Leakage Test
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 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.
• Take out the screws.
• Lift lower casing away from
upper casing.
Troubleshooting chart - see 2.2.
• Remove sprocket cover –
see 3.1.
• Take out the screw (1).
• Remove the cover (2).
• Take out the screw.
• Remove baffle from guide in
upper casing.
• Clean baffle or fit a new one.
Note: If baffle is equipped with
spark arresting screen, make sure
the spark arresting screen is refitted.
Reassemble in the reverse
sequence.
Note: Install a new gasket.
Tighten screws of upper casing to
4 Nm (3 Ibf.ft) and muffler mounting
screws to 11.5 Nm (8.5 Ibf.ft).
• Remove mounting screws from
underside of machine.
• Pull out the muffler.
• Remove the gasket.

STIHL 020 T 17
4.2.2 Pressure Test
4.2.1 Preparations
• Remove the muffler – 4.1.
• Set the piston to top dead center
(T.D.C.). This can be checked
through the exhaust port.
• Fit flange (1) with sleeves (2)
and screws (3) on cylinder
exhaust port. Do not tighten
down yet.
• Slide the sealing plate (4)
between the flange and cylinder
and tighten down the mounting
screws.
Note: The sealing plate must
completely fill the space between
the two mounting screws.
• Remove the carburetor –
see 10.2.1.
• Check that washer (1) and
sleeve (2) are in position.
• Connect tester's pressure hose to
nipple on test flange.
• Make sure the spark plug is
properly tightened down.
• Remove screw (1) from the test
flange (2).
• 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 20 seconds,
the crankcase is airtight.
• Fit the test flange on the
carburetor studs.
• Fit nuts (1) and tighten down
firmly.
If the flange has only three holes,
drill a fourth hole as shown in the
drawing.

STIHL 020 T 18
Note: When you release the pump
piston, the non-return valve auto-
matically seals the suction hose.
If the vacuum reading remains
constant, or rises to no more than
0.4 bar (5.8 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.
• Remove the test flange and refit
the carburetor - see 10.2.
• Remove the flange and sealing
plate.
• Install the muffler - see 4.1.
4.2.3
V
acuum Test
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.
The preparations for this test are
the same as for the pressure test –
see 4.2.1.
• However, if the indicated pressure
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.
• 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 and refit
the carburetor - see 10.2.
• Remove the flange and sealing
plate.
• Install the muffler - see 4.1.
• Pull out the pump piston several
times until the gauge indicates a
vacuum of 0.5 bar (7.25 psi).
• Connect the vacuum pump's suction
hose to test flange nipple.
• Make sure spark plug is tight.

STIHL 020 T 19
4.3 Oil Seals
It is not necessary to disassemble
the complete crankcase if only the oil
seals have to be replaced.
Clutch side:
• Remove the oil pump - see 9.3.1.
• Rotate the angled ends on the
hooks (1) of the puller (3) so that
they are in line with the arms (2).
• Apply the puller, rotate hooks 90°
(angled ends must locate under the
oil seal). Clamp the arms and pull
the oil seal out.
Important: Take special care not to
damage crankshaft stub.
• Clean sealing face on crankshaft
stub with standard commercial,
solvent-based degreasant con-
taining no chlorinated or halogen-
ated hydrocarbons - see 11.2.
• Pack cavity between sealing lip
and oil seal with grease –
see 11.2.
Ignition side:
• Remove the flywheel - see 5.5.
• Apply the puller as at the clutch
side and pull out the oil seal.
Important: Take special care not to
damage crankshaft stub.
• Clean sealing face on crankshaft
stub with standard commercial,
solvent-based degreasant contai-
ning no chlorinated or halogena-
ted hydrocarbons - see 11.2.
• Pack cavity between sealing lip
and oil seal with grease –
see 11.2.
• Push the oil seal over the installing
sleeve (closed side of seal facing
crankcase) and use press sleeve (1)
to press it home.
• Remove the installing sleeve.
• Fit the flywheel - see 5.5.
• Push the oil seal (closed side
facing crankcase) over the
crankshaft and use press sleeve
(1) to press it home.
• Install the oil pump - see 9.3.1.
• Slip the installing sleeve (1) over
the crankshaft. The slot must
locate on the Woodruff key (2).

STIHL 020 T 20
4.4 Cylinder and Piston
4.4.1 Removal
Always check and, if necessary, repair
the fuel system, carburetor, air filter
and ignition system before looking for
faults on the engine.
• Remove the tank housing -
see 10.6.
• Remove the spark plug.
• Now use the assembly drift (2) to
push the piston 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.
Important: Hold the piston steady
during this process to ensure that no
jolts are transmitted to the connecting
rod.
• Remove piston and take the
needle cage out of the connecting
rod.
• Release and unscrew the four
cylinder base screws through the
holes in the cylinder fins.
• Pull the cylinder off the piston.
• Remove the cylinder gasket. • Use a scriber or similar tool to
ease the hookless snap rings out
of the grooves in the piston
bosses.
• Inspect piston rings and replace if
necessary - see 4.5.
• Pull the manifold (1) off the
intake port.
• Inspect the cylinder and replace
it if necessary.
Note: If a new cylinder has to be
installed, always fit the matching
piston. Replacement cylinders are
only supplied complete with piston
for this reason.
Important: Before removing the
piston, decide whether or not the
crankshaft has to be removed as well.
To remove the flywheel, block the
crankshaft by sliding the wooden
assembly block between the piston
and crankcase.