Stihl 4144 Series User manual

STIH)
STIHL Series 4144 Powerhead 2008-01
FS 40, FS 50, FS 56
FC 56
KM 56

1Series 4144 Powerhead
q
© ANDREAS STIHL AG & Co. KG, 2008
RA_938_01_01_01
1. Introduction 2
2. Safety Precautions 3
3. Specifications 4
3.1 Engine 4
3.2 Ignition System 4
3.3 Tightening
Torquese 5
4. Troubleshooting 6
4.1 Clutch 6
4.2 Ignition System 7
4.3 Engine 9
5. Clutch 10
5.1 Clutch Drum 10
5.2 Clutch 11
6. Engine 13
6.1 Leakage Test 13
6.1.1 Preparations 13
6.1.2 Vacuum Test 14
6.1.3 Pressure Test 15
6.2 Oil seals 15
6.3 Removing and
Installing
the Engine 17
6.4 Removing and
Installing
the Cylinder 17
6.5 Crankshaft 21
6.5.1 Removing and
Installing 21
6.6 Bearings /
Crankshaft 23
6.7 Piston 24
6.7.1 Piston Ring 27
7. Ignition System 27
7.1 Ignition Module 28
7.1.1 Removing and
Installing 28
7.2 Ignition Timing 29
7.3 Testing
the Ignition Module 30
7.4 Spark Plug Boot 31
7.5 Flywheel 32
7.6 Ignition System
Troubleshooting 33
8. Special Servicing
Tools 36
9. Servicing Aids 38
Contents

2Series 4144 Powerhead
1. Introduction
This service manual contains
detailed descriptions of all the repair
and servicing procedures specific to
this power tool.
You should make use of the
illustrated parts lists while carrying
out repair work. They show the
installed positions of the individual
components and assemblies.
Refer to the latest edition of the
relevant parts list to check the part
numbers of any replacement parts.
A fault on the machine may have
several causes. To help locate the
fault, consult the troubleshooting
charts for all assemblies and
systems in this manual and the
"STIHL Service Training System".
Refer to the “Technical Information”
bulletins for engineering changes
which have been introduced since
publication of this service manual.
Technical information bulletins also
supplement the parts list until a
revised edition is issued.
The special tools mentioned in the
descriptions are listed in the chapter
on "Special Servicing Tools" in 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:
APointer
aDirection of movement
@4.2 = Reference to another
chapter, i.e. chapter 4.2
in this example
Service manuals and all technical
information bulletins are intended
exclusively for the use of properly
equipped repair shops. They must
not be passed to third parties.
Always use original STIHL
replacement parts.
They can be identified by the STIHL
part number,
the {
logo and the
STIHL parts symbol K
This symbol may appear alone on
small parts.
Storing and disposing of oils
and fuels
Collect fuel or lubricating oil in a
clean container and dispose of it
properly in accordance with local
environmental regulations.

3Series 4144 Powerhead
2. Safety Precautions
If the engine is started up in the
course of repairs or maintenance
work, observe all local and country-
specific safety regulations as well
as the safety precautions and
warnings in the instruction manual.
Gasoline is an extremely flammable
fuel and can be explosive in certain
conditions.
Always wear suitable protective
gloves for operations in which
components are heated for
assembly or disassembly.
Improper handling may result in
burns or other serious injuries.
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.
Always perform leakage test after
working on the fuel system and the
engine.

4Series 4144 Powerhead
3. Specifications
3.1 Engine
FS 40 FS 50, 56, FC 56, KM 56
Displacement: 27.2 cm327.2 cm3
Bore: 34 mm 34 mm
Stroke: 30 mm 30 mm
Engine power to ISO 8893: 0.7 kW (1.0 bhp)
at 8,500 rpm
0.8 kW (1.1 bhp)
at 8,500 rpm
Max. permissible speed
(with cutting attachment): 10,000 rpm 10,000 rpm
Idle speed: 2,800 rpm 2,800 rpm
Clutch: Centrifugal clutch without
linings
Centrifugal clutch without
linings
Clutch engages at: 4,200 rpm 4,200 rpm
Crankcase leakage test
at gauge pressure: 0.5 bar
under vacuum: 0.5 bar
3.2 Ignition System
Air gap between the ignition
module and flywheel: 0.30 mm
Spark plug (suppressed): NGK CMR 6 H
NGK 6 H
Electrode gap: 0.5 mm

5Series 4144 Powerhead
3.3 Tightening Torquese
DG and P (Plastoform) screws are used in polymer and light metal components. These screws form a
permanent thread when they are installed for the first time. They can be removed and installed as often as
necessary without impairing the strength of the screwed assembly, providing the specified tightening torque is
observed.
For this reason it is essential to use a torque wrench.
Fastener Thread size For component Torque
Nm
Remarks
Screw UNC 8-32 Clutch drum/crankshaft 3,5
Carrier 3/8“ -24 Carrier, clutch/crankshaft 20,0 5)
Carrier M 8x1 Carrier, starter side/crankshaft 17,0
Screw D 5x20 Muffler/cylinder 9,0
Screw D 5x20 Spacer flange/cylinder 6,0
Screw D 4x20 Ignition module/cylinder with washer 4,5
M 10x1 Spark plug 12,0
Screw D 5x60 Engine pan/crankcase/cylinder 9,0
Remarks:
1) Loctite 242 or 243, medium strength
2) Loctite 270, high strength
3) Loctite 649, high strength
4) Loctite 272, high strength up to 250°C
5) Degrease crankshaft/flywheel and mount oil-free
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.
Coat micro-encapsulated screws with medium strength Loctite 242 or 243 before reinstalling.
Power screwdriver setting for polymer: DG and P screws max. 500 rpm
Do not use an impact wrench for releasing or tightening screws.
Do not mix up screws with and without binding heads.

6Series 4144 Powerhead
4. Troubleshooting
4.1 Clutch
Condition Cause Remedy
Cutting attachment stops under
load at full throttle
Clutch shoes badly worn Install new clutch
Clutch drum badly worn Install new clutch drum
Cutting attachment runs at idle
speed
Engine idle speed too high Readjust idle speed screw LA
Clutch springs stretched or fatigued Replace the clutch springs or install
new clutch
Clutch spring hooks broken Replace the clutch springs
Loud noises Clutch springs stretched or fatigued Replace all clutch springs
Clutch shoe retainer broken Install new clutch
Clutch shoes and carrier worn Install new clutch

7Series 4144 Powerhead
4.2 Ignition System
Exercise extreme caution while
carrying out maintenance and
repair work on the ignition system.
The high voltages which occur can
cause serious or fatal accidents.
Condition Cause Remedy
Engine runs roughly, misfires,
temporary loss of power
Spark plug boot is loose Press boot firmly onto spark plug
and fit new spring if necessary
Spark plug sooted, smeared with oil Clean the spark plug or replace if
necessary.
If sooting keeps recurring, check air
filter
Fuel/oil mixture
– too much oil
Use correct mixture of fuel and oil
Incorrect air gap between ignition
module and flywheel
Set air gap correctly
Flywheel cracked or has other
damage or pole shoes have turned
blue
Install new flywheel
Ignition timing wrong, flywheel out
of adjustment, key on crankshaft
has sheared off
Locate flywheel properly or install
new flywheel
Weak magnetization in flywheel Install new flywheel
Irregular spark Check operation of switch shaft/
contact springs and ignition
module.
Faulty insulation or break in ignition
lead or short circuit wire. Check
ignition lead/ignition module and
replace ignition module if
necessary.
Check operation of spark plug.
Clean the spark plug or replace if
necessary.
Crankcase damaged (cracks) Install new crankcase

8Series 4144 Powerhead
Condition Cause Remedy
No spark Spark plug faulty Install new spark plug
Faulty insulation or short in short
circuit wire
Check short circuit wire for short
circuit to ground
Break in ignition lead or insulation
damaged
Check ignition lead, replace ignition
module if necessary
Ignition module faulty Install new ignition module

9Series 4144 Powerhead
4.3 Engine
Always check and, if necessary,
repair the following parts before
looking for faults on the engine:
- Air filter
- Fuel system
- Carburetor
- Ignition system
Condition Cause Remedy
Engine does not start easily, stalls
at idle speed, but operates normally
at full throttle
Oil seals in crankcase damaged Replace the oil seals
Crankcase leaking or damaged
(cracks)
Seal or replace the crankcase
Engine does not deliver full power
or runs erratically
Piston ring worn or broken Fit new piston ring
Muffler / spark arresting screen
carbonized
Clean the muffler (inlet and
exhaust), replace spark arresting
screen, replace muffler if necessary
Air filter dirty Replace air filter
Fuel hose kinked or torn Fit new hose or position it free from
kinks
Engine overheating Insufficient cylinder cooling. Air
inlets in rewind starter blocked or
cooling fins on cylinder very dirty
Thoroughly clean all cooling air
openings and the cylinder fins

10 Series 4144 Powerhead
5. Clutch
5.1 Clutch Drum
– Troubleshooting, b4.1
– Remove the engine – see service
manual for "Series 4144
Components – FS, FC, KM"
:Pull boot (1) off the spark plug.
:Unscrew the spark plug (1).
545RA008 TG
1
938RA093 TG
1
:Push the locking strip (1)
0000 893 5904 into the spark
plug hole until it butts against the
cylinder wall (arrow)
as shown.
:Insert screwdriver bit (1) 0812
540 1112 through the clutch drum
(arrow).
– Loosen the screw
– take care not to damage the
screw head.
– Pull off the clutch drum (2).
The mounting screw is inside the
clutch drum. If the screw is
damaged, the clutch drum must be
replaced.
545RA000 TG
1
938RA001 TG
1
2
!
80%
100%
165RA029 TG
1
– Inspect the clutch drum (1) for
signs of wear.
If there are signs of serious wear on
the inside diameter of the clutch
drum (1), check the remaining wall
thickness. If it is less than about
80% of the original thickness, install
a new clutch drum.
– Clean away old mounting paste.
:Coat crankshaft stub (1) with
mounting paste, a = about
10 mm, b9
a
938RA100 TG
1

11Series 4144 Powerhead
– Remove the clutch, b5.2
:Push clutch drum (1) onto
crankshaft stub (arrow) at ignition
side.
– Coat thread of mounting screw
with Loctite, b9
:Insert screwdriver bit (1) 0812
540 1112 through the clutch drum
(arrow).
– Insert and tighten down the screw
firmly – take care not to damage
the screw head.
– Reassemble all other parts in the
reverse sequence.
– Tightening torques, b3.3
938RA002 TG
1
938RA003 TG
1
5.2 Clutch
– Block the piston, b5.1
– Remove the clutch drum, b5.1
:Position the wrench (1) 4130 890
3600 on the crankshaft stub so
that its pins engage the recesses
(arrows).
:Unscrew the clutch (1).
The clutch has a right-hand thread.
938RA013 TG
1
938RA005 TG
1
:Remove the cup spring (1) and
washer (2).
– Check the individual parts and
replace if necessary.
If the clutch shoes are worn or
damaged, the entire clutch must be
replaced together with the cup
spring and washer – see parts list.
Always replace worn or damaged
clutch springs in pairs.
:Push the carrier (1) out of the
clutch shoes (2).
938RA006 TG
2
1
938RA007 TG
1
2

12 Series 4144 Powerhead
:Unhook the springs (1) from the
clutch shoes.
Position the clutch shoes so that the
markings (arrows) are visible.
– Fit new clutch springs.
– Position the carrier (1) so that the
word "OFF" faces up.
The clutch shoes (2) must be
connected by the springs (3)
– the springs (3) must be properly
engaged in the clutch shoes.
:Hold the carrier (1) against one
clutch shoe (2) and hold the other
clutch shoe at an angle against
the carrier (1), pull the shoes
slightly apart and push the carrier
into position.
– Push the carrier (1) into the clutch
shoes (2) as far as stop.
11
M
M
938RA008 TG938RA009 TG
1
3
2
Installing
:Push the washer (2) and cup
spring (1) onto the crankshaft
stub.
The cup spring (1) must be properly
seated in the carrier (arrow) and
must not slip out of position while
the clutch is being screwed home.
:Fit the clutch so that the word
"OFF" (arrow) faces up.
938RA010 TG
2
1
938RA011 TG
1
938RA012 TG
:Position the wrench (1)
4130 890 3600 on the crankshaft
stub so that its pins engage the
recesses (arrows).
:Check position of locking strip
(1).
:Tighten down the clutch (1)
firmly.
– Tightening torques, b3.3
– Remove the locking strip from the
cylinder.
– Reassemble all other parts in the
reverse sequence.
938RA013 TG
1
938RA014 TG
1
938RA096 TG
1

13Series 4144 Powerhead
6. Engine
Removal and installation of the
engine is described in the service
manual for "Series 4144
Components – FS, FC, KM".
6.1 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 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.
Always perform the vacuum test
first and then the pressure test.
The engine can be checked
thoroughly for leaks with the pump
0000 850 1300.
The engine does not need to be
removed for the leakage test.
6.1.1 Preparations
– Remove the fan housing – see
service manual for "Series 4144
Components – FS, FC, KM"
– Remove the spark plug boot with
cap.
:Unscrew the spark plug (1).
– Set the piston to top dead center.
This can be checked through the
spark plug hole.
– Fit the spark plug (1) and tighten
it down firmly.
– Tightening torques, b3.3
:Loosen the screws (arrows).
– Lift the muffler (1).
938RA093 TG
1
938RA015 TG
1
:Fit the sealing plate (1)
0000 855 8106 between the
cylinder exhaust port and muffler
and tighten down the screws
moderately.
The sealing plate must completely
fill the space between the two
screws.
– Remove the carburetor
– see service manual for
"Series 4144 Components – FS,
FC, KM"
Check that the gasket (1) is in
position.
938RA016 TG
1
938RA017 TG
1

14 Series 4144 Powerhead
The new flange 5910 850 4200
replaces the previous flange 1128
850 4200. The new flange has an
additional recess (arrow) in its
sealing face. The previous flange
1128 850 4200 can be modified
accordingly.
Modify the test flange
1128 850 4200 as shown.
:Fit the test flange (1)
5910 850 4200.
938RA097 TG
3
O 16
296RA009 TG938RA018 TG
1
:Fit the nuts (arrows) and tighten
them down firmly.
6.1.2 Vacuum Test
Oil seals tend to fail when subjected
to a vacuum, i.e. the sealing lip lifts
away from the crankshaft during the
piston's induction stroke because
there is no internal counterpressure.
A test can be carried out with pump
0000 850 1300 to detect this kind of
fault.
:Connect suction hose (1) of
pump 0000 850 1300 to
nipple (arrow).
938RA019 TG938RA020 TG
1
:Push ring (1) to the left.
:Operate the lever (2) until the
pressure gauge (arrow) indicates
a vacuum of 0.5 bar.
If the vacuum reading remains
constant, or rises to no more than
0.5 bar 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
engine), the oil seals must be
replaced, b6.2.
– After finishing the test, push the
ring to the right to vent the pump.
– Continue with pressure test,
b6.1.3
938RA021 TG
1
2

15Series 4144 Powerhead
6.1.3 Pressure Test
Carry out the same preparations as
for the vacuum test, b6.1.2
– Always carry out the vacuum test,
before the pressure test, b6.1.2
:Connect pressure hose (1) of
pump 0000 850 1300 to nipple
(arrow).
:Push ring (1) to the right.
:Operate the lever (2) until the
pressure gauge (arrow) indicates
a pressure of 0.5 bar. If this
pressure remains constant for at
least 20 seconds, the engine is
airtight.
– If the pressure drops below 0.5
bar within 20 seconds, the leak
must be located and the faulty
part replaced.
938RA020 TG
1
938RA022 TG
1
2
To find the leak, coat the suspect
area with oil and pressurize the
engine. Bubbles will appear if a leak
exists.
– After finishing the test, push the
ring to the left to vent the pump –
disconnect the hose.
– Remove the test flange.
– Install the carburetor
– see service manual for
"Series 4144 Components – FS,
FC, KM"
– Loosen the muffler and pull out
the sealing plate.
– Tighten down the muffler firmly.
– Reassemble all other parts in the
reverse sequence.
– Tightening torques, b3.3
6.2 Oil seals
It is not necessary to disassemble
the engine to replace the oil seals.
Ignition side
– Remove the engine – see service
manual for "Series 4144
Components – FS, FC, KM"
– Remove the flywheel, b7.5
– Free off the oil seal in its seat by
tapping it with a suitable tube or a
punch.
:Apply puller (1) 5910 890 4400
with No. 3.1 jaws 0000 893 3706.
– Clamp the puller arms.
– Pull out the oil seal.
Take care not to damage the
crankshaft stub.
– Clean the sealing face, b9
– Lubricate sealing lips of new oil
seal with grease, b9
938RA023 TG
1

16 Series 4144 Powerhead
– Apply a thin coating of sealant to
the outside diameter of the oil
seal, b9
– Carefully push the oil seal, open
side facing the engine, over the
crankshaft stub
– avoid touching the thread so as
not to damage the rubber lip.
:Use press sleeve (2)
1129 893 2400 to install the oil
seal (1).
The seating face must be flat and
free from burrs.
– Wait about one minute, then
rotate the crankshaft several
times.
– Degrease the crankshaft taper,
b9
– Reassemble all other parts in the
reverse sequence.
938RA024 TG
21
Carrier side
– Remove the engine – see service
manual for "Series 4144
Components – FS, FC, KM"
– Block the piston, b5.1
:Apply wrench to hexagon (arrow)
and unscrew the carrier (1).
– Free off the oil seal in its seat by
tapping it with a suitable tube or a
punch.
:Apply puller (1) 5910 890 4400
with No. 3.1 jaws 0000 893 3706.
– Clamp the puller arms.
– Pull out the oil seal.
1
938RA025 TG
1
938RA026 TG
Take care not to damage the
crankshaft stub.
– Clean the sealing face, b9
– Lubricate sealing lips of new oil
seal with grease, b9
:Fit the installing sleeve (1)
4119 893 4600.
– Apply a thin coating of sealant to
the outside diameter of the oil
seal, b9
– Slip the oil seal, closed side
facing outwards, over the
installing sleeve.
– Remove the installing sleeve (1).
1
938RA027 TG

17Series 4144 Powerhead
:Use press sleeve (1)
1121 893 2400 to install the oil
seal (2).
– Wait about one minute, then
rotate the crankshaft several
times.
– Install the engine – see service
manual for "Series 4144
Components – FS, FC, KM"
– Tightening torques, b3.3
6.3 Removing and Installing
the Engine
The complete engine has to be
removed for access to the piston,
cylinder and crankshaft.
See service manual for "Series
4144 Components – FS, FC, KM"
1
938RA028 TG
2
938RA029 TG
6.4 Removing and Installing
the Cylinder
Before removing the piston, decide
whether or not the crankshaft,
clutch or carrier have to be removed
as well.
Cylinder installed
To remove the clutch or carrier,
block the.crankshaft by inserting the
locking strip in the spark plug hole.
Cylinder removed
To remove the clutch or carrier,
block the crankshaft by resting the
piston on the wooden assembly
block 1108 893 4800.
– Remove the engine and pull off
the carburetor – see service
manual for "Series 4144
Components – FS, FC, KM"
938RA029 TG
:Take out the screws (arrows).
– Remove the muffler (1).
– Remove the ignition module (2),
b7.1.1
– Prepare the puller (1) 5910 890
4400.
:Fit the No. 2 jaws (2)
0000 893 3700.
:Screw the bushing (3)
1108 893 4500 onto the puller's
spindle.
938RA030 TG
2
1
296RA033 TG
2
3
1

18 Series 4144 Powerhead
:Apply the puller (1) 5910 890
4400 with the jaws under the
crankcase ribs (arrows) and line
up the spindle (2) so that the
bushing (3) is centered on the
engine pan.
:Turn the spindle (2) clockwise
until the puller sits tightly.
Do not overtighten the spindle
because the jaws may slip off or
damage the crankcase ribs.
:Take out the cylinder screws
(arrows).
1
2
3
938RA031 TG938RA032 TG
:Carefully lift the cylinder (1)
away.
Do not use pointed or sharp-edged
tools for this job.
– Check the cylinder and replace if
necessary.
:Remove the cylinder gasket (1).
– Inspect and clean the sealing
face (arrow), b9
The sealing face must be in perfect
condition. Always replace
components with damaged sealing
faces, b4.3.
938RA033 TG
1
938RA034 TG
1
938RA035 TG
Always use a new cylinder gasket
when re-installing the cylinder.
– Line up the cylinder gasket (1) so
that the tab and cutouts (arrows)
match the contours of the
crankcase.
:Place the cylinder gasket (1) in
position.
– Inspect the spacer flange (1) and
replace it if necessary – even
very minor damage can result in
engine running problems, b4.3
In a new cylinder is installed, the
spacer flange must be transferred
from the old cylinder.
938RA036 TG
1
938RA037 TG
1

19Series 4144 Powerhead
:Take out the screws (arrow)
together with the connector tag.
– Remove the spacer flange (1).
– Remove the gasket (1)
– always install a new gasket
:Inspect and clean the sealing
faces (arrows) and remove any
gasket residue, b9
– Check the sealing faces on the
cylinder intake and exhaust ports.
938RA038 TG
1
545RA207 TG
1
938RA039 TG
The sealing faces must be in perfect
condition. If the sealing faces are
damaged, install a new cylinder or
spacer flange.
– Inspect the piston and piston
rings and replace if necessary,
b6.7
:Slide the wooden assembly block
(1) 1108 893 4800 between the
piston and crankcase.
– Lubricate the piston, piston ring
and cylinder wall with oil, b9
:Use the clamping strap (1)
0000 893 2600 to compress the
ring around the piston.
938RA040 TG
1
938RA041 TG
1
– Check correct installed position
of ring, b6.7.1
Apply the clamping strap (1) so that
the piston ring does not project
beyond the cylinder wall.
:Align the cylinder so that the
recess in the cylinder engages
the projection on the crankcase
(arrows).
Take care not to damage the
cylinder gasket.
While sliding the cylinder over the
piston, hold the clamping strap
tightly around the piston so that the
ring does not project
– it might otherwise break.
:Slide the cylinder over the piston,
the clamping strap moves
downwards at the same time.
296RA046 TG938RA042 TG