Stihl MS 240 User manual

STIH)
STIHL MS 240, 260 2013-09

1MS 240, MS 260, MS 260 C
q
© ANDREAS STIHL AG & Co. KG, 2013
RA_165_00_01_05
1. Introduction 3
2. Safety Precautions 5
3. Specifications 6
3.1 Engine 6
3.2 Fuel System 6
3.3 Ignition System 6
3.4 Chain Lubrication 6
3.5 Tightening Torquese 7
4. Troubleshooting 9
4.1 Clutch 9
4.2 Chain Drive,
Chain Brake,
Chain Tensioner 10
4.3 Chain Lubrication 11
4.4 Rewind Starter 12
4.5 Ignition System 13
4.6 Carburetor 15
4.7 Engine 18
5. Cutting Attachment 19
5.1 Chain Catcher 19
6. Clutch 20
6.1 Clutch Drum 22
7. Chain Brake 23
7.1 Checking Operation 23
7.2 Removing and Installing
the Brake Band 23
7.3 Brake Lever 25
7.4 Cam Lever 26
7.5 Pins 27
7.6 Side Chain Tensioner 28
7.6.1 Front Chain Tensioner 29
7.6.2 Quick Chain
Tensioner 29
7.7 Bar Mounting Studs 30
8. Engine 31
8.1 Muffler / Spark
Arresting Screen 31
8.2 Leakage Test 32
8.2.1 Preparations 33
8.2.2 Vacuum Test 34
8.2.3 Pressure Test 34
8.3 Oil Seals 35
8.4 Removing and
Installing the Shroud 36
8.5 Cylinder 37
8.6 Crankshaft 40
8.6.1 Removing and
Installing 40
8.6.2 Bearings / Crankcase 45
8.7 Piston 47
8.7.1 Removal 47
8.7.2 Installing 48
8.8 Piston Rings 49
8.9 Decompression Valve 50
9. Ignition System 51
9.1 Ignition Timing 51
9.2 Ignition Module 51
9.2.1 Removing and
Installing 51
9.3 Testing the
Ignition Module 54
9.4 Spark Plug Boot /
Ignition Lead 55
9.5 Flywheel 56
9.6 Short Circuit Wire 57
9.6.1 Testing 57
9.6.2 Removing and
Installing 57
9.6.3 Ground Wire 60
9.7 Ignition System
Troubleshooting 61
10. Rewind Starter 64
10.1 General 64
10.2 Removing and
Installing 64
10.3 Pawl 64
10.4 Rope Rotor 65
10.5 Starter Rope / Grip 66
10.6 Tensioning the Rewind
Spring 67
10.7 Replacing the Rewind
Spring 68
11. Servicing the
AV System 70
11.1 Annular Buffer on
Chain Catcher 70
11.2 Annular Buffer at
Clutch Side 70
11.3 Annular Buffer at
Ignition Side 71
11.4 Stop Buffer 72
11.5 Handlebar 72
11.6 Handlebar with
Handle Heating 73
12. Control Levers 76
12.1 Switch Shaft 76
12.1.1 Removing and
Installing 76
12.2 Throttle Trigger/Interlock
Lever 77
13. Chain Lubrication 80
13.1 Pickup Body 80
13.2 Oil Suction Hose 80
13.3 Oil Delivery Hose 81
13.4 Non-Adjustable
Oil Pump 81
13.5 Adjustable Oil Pump 82
13.6 Valve 83
14. Fuel System 85
14.1 Air Filter 85
14.2 Removing and Installing
the Carburetor 85
14.3 Leakage Test 86
14.4 Servicing the
Carburetor 87
14.4.1 Inlet Needle 89
14.4.2 Fixed Jet 89
14.4.3 Pump Diaphragm 90
14.4.4 Choke Shaft /
Choke Shutter 91
14.4.5 Adjusting Screws 91
14.5 Adjusting the
Carburetor 92
14.5.1 Basic Setting 92
14.5.2 Standard Setting 93
Contents

2MS 240, MS 260, MS 260 C
Contents
14.6 Throttle Rod 94
14.6.1 Removing and Installing
the Intake Manifold 94
14.6.2 Impulse Hose 96
14.7 Tank Vent 96
14.7.1 Testing 96
14.7.2 Removing and
Installing 97
14.8 Fuel Intake 98
14.8.1 Pickup Body 98
14.8.2 Fuel Suction Hose 98
14.8.3 Removing and Installing
the Tank Housing 99
15. Heating System 100
15.1 Carburetor Heating 100
15.1.1 Testing the Complete
System 100
15.1.2 Testing the Heating
Element 100
15.1.3 Thermostatic Switch 101
15.2 Carburetor Heating
System Troubleshooting
Chart 103
15.3 Handle Heating
System 104
15.3.1 Troubleshooting 104
15.4 Removing and Installing
the Heater Switch 104
15.4.1 Heater Switch
Ground Wire 105
15.5 Removing and Installing
Heating Element in
Rear Handle 106
15.6 Removing and Installing
the Heating Element
in the Handlebar 108
15.7 Removing and Installing
the Generator 108
15.7.1 Handle Heating and
Generator Trouble-
shooting Chart 110
15.7.2 Test Connections and
Test Values 112
15.8 Wiring Harness 114
16. Special Servicing
Tools 116
17. Servicing Aids 118

3MS 240, MS 260, MS 260 C
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.
Servicing and repairs are made
considerably easier if the machine
is mounted to assembly stand (3)
5910 890 3100. To do this, secure
the mounting plate (2) 5910 850
1650 to the assembly stand with two
screws (1) and washers.
The screws must not project since
they, depending on the machine,
may damage housings when the
machine is clamped in position.
The above operation is not
necessary with the new assembly
stand 5910 890 3101 since the
mounting plate is already fitted.
1
2
3
219RA000 TG

4MS 240, MS 260, MS 260 C
Engage the bar mounting studs in
the outer bores in the mounting
plate and secure the saw in position
with the nuts (arrows).
The chain sprocket cover and
cutting attachment have to be
removed before mounting the saw
to the assembly stand – pull the
hand guard toward the handlebar.
165RA000 TG
Versions with Quick Chain
Tensioner
There is only one bar stud on these
versions. It is pushed through the
upper hole (arrow) in the mounting
plate and secured with the nut (1).
The machine is held in position on
the mounting plate by the screw
heads on the crankcase.
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.
165RA468 TG
1

5MS 240, MS 260, MS 260 C
2. Safety Precautions
If the power tool 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.

6MS 240, MS 260, MS 260 C
3. Specifications
3.1 Engine
MS 240 MS 260, MS 260 C
Displacement: 41.6 cm350.2 cm3
Bore: 42 mm 44.7 mm
Stroke: 30 mm 32 mm
Engine power to ISO 7293: 2.1 kW (2.85 bhp)
at 9500 rpm
2.6 kW (3.5 bhp)
at 9500 rpm
Maximum permissible engine speed
(with bar and chain): 13000 rpm 14000 rpm
Versions with catalytic converter
Maximum permissible engine speed
(with bar and chain):
13000 rpm
Idle speed: 2800 rpm 2800 rpm
Clutch: Centrifugal clutch without
linings
Centrifugal clutch without
linings
Clutch engages at: 3600 rpm 3600 rpm
Crankcase leakage test
at gauge pressure: 0.5 bar
under vacuum: 0.5 bar
3.2 Fuel System
Carburetor leakage test at
gauge pressure:
0.8 bar
Operation of tank vent at
gauge pressure:
0.5 bar
Fuel: as specified in instruction
manual
3.3 Ignition System
Air gap between ignition
module and fanwheel: 0.15...0.30 mm
Spark plug (suppressed): NGK BPMR 7 A
Electrode gap: 0.5 mm
3.4 Chain Lubrication
Speed-controlled oil pump with reciprocating piston and
manual flow control
Oil pump without adjustable
delivery rate:
7.5 (+/- 2.5) cm3/min at
10000 rpm
Oil pump with adjustable
delivery rate:
4.5...11.5 cm3/min at
10000 rpm

7MS 240, MS 260, MS 260 C
3.5 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
Letter
Countersunk screw P 4x12 Cover plate/sprocket cover (quick chain
tensioner)
2.5
Screw M 4x8 Cover plate/chain tensioner 3.0 4)
Collar screw M 8x21.5 Bar mounting 23.0 1)
Collar screw M10/M 8 Bar mounting/quick chain tensioner 30.0 1)
Screw M 4x12 Cover, chain brake/crankcase 3.0 4)
M 10x1 Decompression valve (MS 260) 14.0
Screw B 4.9x9.5 Spark arresting screen/muffler 2.0
Screw M 3.5x12 Generator/crankcase 2.0 1)
Screw P 6x32.5 Handlebar, top (polymer)/tank housing 5.0
Screw P 6x21.5 Handlebar, bottom (polymer)/tank housing 5.0
Screw P 6x19 Handlebar, top and bottom/tank housing
(version with handle heating)
7.0
Screw P 4x19 Handle molding 1.6
Screw M 5x12 Retaining plate/annular buffer 8.0 4)
Screw M 4x16 Hand guard/crankcase (micro-encapsulated) 4.0 4)
Nut M 5 Slotted nut, shroud/stud, cylinder 3.5
Screw P 6x19 Chain catcher/plug 2.8
Screw M 5x12 Spiked bumper
(with self-locking nut) 7.5
4)
Screw M 5x20 Crankcase 9.0
Collar nut M 5 Air filter/tank housing 2.0
Screw M 4x16 Fan housing 4.0 4)
M 12x1L Carrier (clutch) 50.0
Screw M 4x12 Oil pump/crankcase 3.0 4)
Screw P 6x26.5 Annular buffer, tank housing/crankcase
(ignition side)
5.0
Screw M 5x12 Annular buffer plate/crankcase (ignition side) 8.0 4)
Screw P 6x19 Annular buffer, tank housing/crankcase
(clutch side)
5.5
Screw M 5x16 Muffler/crankcase/cylinder
(version with catalytic converter and MS 260)
10.0 1), 4)

8MS 240, MS 260, MS 260 C
Fastener Thread size For component Torque
Nm
Remarks
Screw M 5x12 Muffler/crankcase/cylinder (MS 240) 10.0 1), 4)
Nut M 8x1 Flywheel 33.0 3)
Screw M 4x8 Side plate/crankcase 3.0 4)
Screw M 4x16 Side plate/crankcase (quick chain tensioner) 3.0
Screw M 3x20 Clamp/manifold 0.5
M 5x8.5 Stud/cylinder 1.4 2)
Nut M 5 Carburetor 3.5
Screw M 5x20 Cylinder/crankcase 11.0 2), 4)
M 14x1.25 Spark plug 25.0
Screw M 5x20 Ignition module/crankcase (micro-
encapsulated)
7.0 4)
Remarks:
1) Loctite 242 or 243, medium strength
2) Loctite 270, high strength
3) Degrease crankshaft/flywheel and mount oil-free
4) Screws with binding head
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.

9MS 240, MS 260, MS 260 C
4. Troubleshooting
4.1 Clutch
Condition Cause Remedy
Saw chain stops under load at full
throttle
Clutch shoes badly worn Install new clutch
Clutch drum badly worn Install new clutch drum
Saw chain rotates at idle speed Engine idle speed too high Readjust with idle speed screw LA
(counterclockwise)
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
Needle cage damaged Fit new needle cage
Clutch shoe retainer broken Fit new retainer
Clutch shoes and carrier worn Install new clutch

10 MS 240, MS 260, MS 260 C
4.2 Chain Drive, Chain Brake, Chain Tensioner
Condition Cause Remedy
Chain sprocket wears rapidly Chain not properly tensioned Tension chain as specified
Wrong chain pitch Fit chain of correct pitch
Insufficient chain lubrication Check chain lubrication
Chain sprocket worn Fit new chain sprocket
Saw chain stops under load at full
throttle
Clutch shoes badly worn Install new clutch
Clutch drum badly worn Install new clutch drum
Brake band blocked Check freedom of movement and
operation of brake band
Saw chain rotates at idle speed Engine idle speed too high Readjust with idle speed screw LA
(counterclockwise)
Clutch springs stretched or fatigued Replace the clutch springs or install
new clutch
Clutch spring hooks broken Replace the clutch springs
Saw chain does not stop
immediately when brake is
activated
Brake spring stretched or broken Fit new brake spring
Brake band stretched or worn Fit new brake band
Clutch drum worn Install new clutch drum

11MS 240, MS 260, MS 260 C
4.3 Chain Lubrication
In the event of trouble with the
chain lubrication system, check and
rectify other sources of faults
before disassembling the oil pump.
.
Condition Cause Remedy
Chain receives no oil Oil tank empty Fill up with oil and check setting of
oil pump if necessary
Oil inlet hole in guide bar is blocked Clean oil inlet hole
Intake hose or pickup body clogged
or intake hose ruptured
Fit new intake hose and pickup
body
Valve in oil tank blocked Clean or replace valve
Teeth on worm worn Install new worm
Oil pump damaged or worn Install new oil pump
Machine losing chain oil Oil pump body damaged Install new oil pump
Oil pump damaged or worn Install new oil pump
Oil suction hose connection
damaged
Install new oil intake hose
Oil pump delivers insufficient oil Oil pump worn Install new oil pump
Oil pump delivery rate set too low Adjust oil pump
(only on version with adjustable oil
pump)

12 MS 240, MS 260, MS 260 C
4.4 Rewind Starter
Condition Cause Remedy
Starter rope broken Rope pulled out too vigorously as
far as stop or over edge, i.e. not
vertically
Fit new starter rope
Normal wear Fit new starter rope
Starter rope does not rewind Very dirty or corroded Clean or replace rewind spring
Insufficient spring tension Check rewind spring and increase
tension
Rewind spring broken Fit new rewind spring
Starter rope cannot be pulled out
far enough
Spring overtensioned Check rewind spring and reduce
tension
Starter rope can be pulled out
almost without resistance
(crankshaft does not turn)
Guide peg on pawl or pawl itself is
worn
Fit new pawl
Spring clip on pawl fatigued Fit new spring clip
Starter rope is difficult to pull or
rewinds very slowly
Starter mechanism is very dirty Thoroughly clean complete starter
mechanism
Lubricating oil on rewind spring
becomes viscous at very low
outside temperatures (spring
windings stick together)
Coat rewind spring with a little
standard solvent-based degreasant
(containing no chlorinated or
halogenated hydrocarbons), then
pull rope carefully several times
until normal action is restored
Decompression valve is not open Open, check and replace
decompression valve if necessary

13MS 240, MS 260, MS 260 C
4.5 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
Ignition lead loose in ignition
module
Secure ignition lead properly
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 in flywheel has
sheared off
Fit key if necessary and secure
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

14 MS 240, MS 260, MS 260 C
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 and replace if
necessary
Ignition module faulty Install new ignition module

15MS 240, MS 260, MS 260 C
4.6 Carburetor
Condition Cause Remedy
Carburetor floods; engine stalls Inlet needle not sealing
– foreign matter in valve seat or
cone
Remove and clean the inlet needle,
clean the carburetor
Inlet control lever sticking on
spindle
Check inlet control lever, replace if
necessary
Helical spring not located on nipple
of inlet control lever
Remove the inlet control lever and
refit it correctly
Perforated disc on diaphragm is
deformed and presses constantly
against the inlet control lever
Fit a new metering diaphragm
Metered diaphragm deformed Fit a new metering diaphragm
Poor acceleration Setting of low speed screw too lean Check basic carburetor setting,
correct if necessary
Setting of high speed screw too
lean
Check basic carburetor setting,
correct if necessary
Inlet needle sticking to valve seat Remove inlet needle, clean and
refit
Diaphragm gasket leaking Fit new diaphragm gasket
Metering diaphragm damaged or
shrunk
Fit a new metering diaphragm
Impulse hose damaged or kinked Install new impulse hose
Tank vent faulty Replace tank vent
Leak on fuel hose from tank to
carburetor
Seal connections or install new fuel
hose

16 MS 240, MS 260, MS 260 C
Condition Cause Remedy
Engine will not idle, idle speed too
high
Throttle shutter opened too wide by
idle speed screw LA
Reset idle speed screw LA
correctly
Oil seals/crankcase leaking Seal or replace oil seals/crankcase
Engine stalls at idle speed Idle jet bores
or ports blocked
Clean the carburetor
Setting of low speed screw too rich
or too lean
Reset low speed screw Lcorrectly
Setting of idle speed screw LA
incorrect – throttle shutter
completely closed
Reset idle speed screw LA
correctly
Tank vent faulty Replace tank vent
Leak on fuel hose from tank to
carburetor
Seal connections or install new fuel
hose

17MS 240, MS 260, MS 260 C
Condition Cause Remedy
Engine speed drops quickly under
load – low power
Air filter dirty Clean air filter or replace if
necessary
Throttle shutter not opened fully Check throttle cable and rod
Tank vent faulty Replace tank vent
Fuel pickup body dirty Install new pickup body
Fuel strainer dirty Clean fuel strainer in carburetor,
replace if necessary
Leak on fuel hose from tank to
carburetor
Seal connections or install new fuel
hose
Setting of high speed screw H
too rich
Check basic carburetor setting,
correct if necessary
Main jet bores or ports blocked Clean the carburetor
Pump diaphragm damaged or
fatigued
Fit new pump diaphragm
Impulse hose damaged or kinked Install new impulse hose
Ignition timing wrong, flywheel out
of adjustment, key in flywheel is
missing or has sheared off
Fit key if necessary and secure
flywheel properly or install new
flywheel

18 MS 240, MS 260, MS 260 C
4.7 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 rings worn or broken Fit new piston rings
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/impulse hose severely kinked
or damaged
Fit new hoses or position them free
from kinks
Decompression valve is not closed Close, check and replace
decompression valve if necessary
Engine overheating Insufficient cylinder cooling. Air
inlets in fan housing blocked or
cooling fins on cylinder very dirty
Thoroughly clean all cooling air
openings and the cylinder fins

19MS 240, MS 260, MS 260 C
5. Cutting Attachment
Wear gloves to protect your hands
from injury.
:Unscrew the hex nuts (1).
:Remove the chain sprocket
cover (2).
:Remove the guide bar (3) with
chain.
– Reassemble in the reverse
sequence.
Versions with Quick Chain
Tensioner
Wear gloves to protect your hands
from injury.
:Swing the wing nut (1) upright
and loosen it counterclockwise.
:Remove the sprocket cover (2)
and tensioning gear (3) with
guide bar (4).
– Reassemble in the reverse
sequence.
1
2
3
165RA002 TG
2
1
4
165RA464 TG
3
:Carefully pry the wing nut (1) out
of the sprocket cover (arrow).
– Check the wing nut (1) and
replace if necessary
– Swing the wing nut (1) upright.
:Push the wing nut (1), thin side
first (see arrow), into the opening
and press it down until it snaps
into positon.
:Take out the screw (arrow).
– Remove the cover plate (1) and
adjusting wheel (2).
1
165RA469 TG
1
165RA007 TG
1
165RA455 TG
2
When installing the adjusting wheel,
make sure its teeth point
inboard.
– Reassemble in the reverse
sequence.
5.1 Chain Catcher
– Remove the sprocket cover and
cutting attachment, b5
:Take out the screw (arrow) and
remove the chain catcher (1).
– Reassemble in the reverse
sequence.
– Tightening torques, b3.5
165RA247 TG
1