Technical Information · issue 18 of 2010
New STIHL MS 261, MS 261 C Chain Saws
IssueTI 18/2010
Engine family 1141
Full text
Page 1 of 15
STIH) Technical Information 18.2010 New STIHL MS 261, MS 261 C Chain Saws – Series 1141 Contents 1. Technical Description 2. Specifications 3. Servicing Accessories and Special Tools 4. Service note TI_18_2010_30_01_01.fm englisch / English
Page 2 of 15
Page 2 Technical Information 18.2010
The new MS 261 provides the following features 1. Technical Description
through innovative technology.
– Modern low-emission engine with reduced fuel 1.1 Pre-separation
consumption.
– High torque over broad RPM range combined
with free-revving characteristics for limbing
operations.
– Longlife air filter system consisting of pre-
separation, HD2 air filter and compensator for a
much longer filter life.
– Professional anti-vibration system for low
vibrations and optimum control behavior.
– Other details: One-piece shroud with three
quick-release locks, captive nuts on chain
sprocket cover, air filter with bayonet lock and
stainless steel muffler.
The new STIHL MS 261 chain saw for thinning work
and harvesting small-sized timber or logging in
5902TI004 KN
medium stands as well as cutting firewood and
woodworking projects.
The following versions are available: Intake air is caused to rotate and deflected
– MS 261 horizontally by the ramp in front of the ignition
module. Larger and heavier airborne particles (black
– MS 261 C-Q with STIHL Quickstop® Plus chain arrows) are thrown upwards and outwards.
brake system Pre-cleaned air (gray arrows) flows via the pre-
separator channel to the air filter.
1.2 Longlife air filter system
The combination of pre-separator,
HD2 air filter and compensating carburetor achieves
a filter life up to five times longer than the previous
model.
The new filters feature a new radial seal. This
reduces the ingress of dirt into the air filter‘s clean
air chamber.
The air filter system can be adapted to suit different
operating conditions by installing different filters.
Changing a filter is accomplished quickly and
simply.
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Technical Information 18.2010 Page 3
1.2.1 HD2 air filter
5902TI006 KN
5902TI005 KN
. Rotate the air filter one quarter turn
– HD2 filter: counterclockwise and pull it away in direction of
Black filter frame, pleated filter material rear handle.
The new filter material is characterized by its oil and Always replace a damaged filter.
water repellent properties, a more than 70% better Cleaning the air filter
retention rate compared to conventional filter
. Knock out the filter or blow it clear with low psi
concepts and the fact that it is very easy to clean.
compressed air from the inside outwards.
The filter retains its properties even after countless
cleaning cycles. The HD2 filter's material is pleated In case of stubborn dirt or sticky filter fabric:
to achieve a large surface area. . Wash the filter in STIHL special cleaner (special
Suitability accessory) or clean, non-flammable solution
(e.g. warm soapy water) – rinse the filter from
For normal, dry or very dusty work areas.
the inside outwards under a jet of water – do not
use a pressure washer.
1.2.2 Fabric filter
Dry all parts of the filter – do not use extreme heat.
The fabric filter is particularly suitable for use in
extreme wintry conditions (e.g. in powdery or drifting
snow, frost).
The special structure of the filter ensures good filter
efficiency and life under these operating conditions.
1.2.3 Removing, cleaning and installing the
air filter
The filter can be removed from the filter base
without the need for tools.
Removing the air filter
. Remove the shroud and clean away loose dirt
from around the filter.
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Page 4 Technical Information 18.2010
Installing the air filter 1.4 Reduced emissions engine
Reduced emissions engine technology has been
implemented in the MS 261 without an additional
pure air port, without an air valve and without a
double manifold.
Previous chain saws with reduced emissions engine
(stratified scavenging) feature an additional pure air
1
2 port, air valve and double intake manifold.
Method of operation
5902TI007 KN
. Place the air filter in position.
. Push the air filter in the direction of the filter
housing and turn it clockwise at the same time
until it engages – the filter is correctly installed
when the name "STIHL" is horizontal.
. Fit the shroud.
1.3 Anti-vibration system
2
1
5902TI003 KN
3
6
In the MS 261 the baffle divides the intake air into
two streams. In the carburetor there are
partitions (1) between the choke and throttle
5902TI009 KN
shutters and in the direction of the manifold which
6 6 5 4 1 separate the fresh mixture and air paths at full
throttle.
The new anti-vibration system consists of spring (1),
The space required by the carburetor and intake
springs (2) and (3) with integral shearing element,
manifold is almost the same as for a conventional
the Cellasto AV element (4), the Cellasto stop
two-stroke engine without stratified scavenging.
buffer (5) and the stop buffers (6).
. This combination of elements results in very low
vibration levels and optimum control.
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Technical Information 18.2010 Page 5
1.5 Shroud 1.6 Chain sprocket cover with captive nuts
One-piece shroud with three quick-action locks for
quick and easy access to the air filter and cylinder.
5902TI010 KN
Nuts are permanently connected to the chain
sprocket cover and cannot be lost. The nuts are
always correctly positioned when fitting the sprocket
cover. Each nut can be tightened down independent
of the other. Fewer operations are necessary.
Note
This sprocket cover can only be used on the MS
261. Retrofitting other models is not possible. The
length and shape of the collar studs must be
matched to the sprocket cover with captive nuts.
5902TI008 KN
. Open the quick-action locks (1) by rotating
them a 1/4 turn counterclockwise with the
combination wrench.
. Remove the shroud (2).
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Page 6 Technical Information 18.2010
1.7 Tank caps Warning:This mode of activation of the chain brake
The toolless tank cap with hinged grip is designed is not designed to reduce the risks of injury from
for quick and simple handling. kickback. Rather, the trigger lockout activation
mode for the chain brake primarily serves as a
Large and easily accessible tank openings ensure convenience item for the operator.
trouble-free refueling.
The Quickstop® Plus is available only on STIHL
1.8 STIHL Quickstop® Plus chain brake MS 261 C-Q, MS 280 C-BQ,
system (MS 261 C-Q) MS 361 C-BQ, MS 362 C-Q and MS 441 C-Q.
The STIHL Quickstop® Plus chain brake system is a
unique convenience feature when: 2. Specifications
– Carrying a chain saw 2.1 Engine
– Handling a chain saw during short interruptions STIHL single cylinder two-stroke engine
in cutting
Displacement: 3.06 cu. in.
(50.2 cm3)
Function Bore: 4.47 cm (44.7 mm)
In this activation system the clutch drum is clamped Stroke 3.20 cm (32 mm)
by the hand brake, stopping movement of the chain, Engine power to ISO 7293: 3.8 bhp (2.8 kW)
when the right hand is completely removed from the at 9,500 rpm
throttle trigger and the trigger lockout is released. Idle speed: 2,800 rpm
The trigger lockout acts as the activating High speed setting when
mechanism for this mode of chain brake performing repairs (with bar
engagement. and chain): 14,000 rpm
The brake band releases the clutch drum when the
2.2 Weight
trigger lockout is pressed down again, allowing the
chain to move. Weight (dry, without bar and chain)
This means the chain brake on chain saws MS 261: 11.5 lbs. (5.2 kg)
equipped with the Quickstop® Plus activation
2.3 Ignition System
system can be activated in three different ways:
Ignition module: Electronically controlled
– Manually, either by the operator intentionally
with ignition timing
tripping the front hand guard by pushing it
forward or by the front hand guard tripping as a Spark plug NGK BPMR 7 A
result of contact with the operator´s hand during (resistor type): Bosch WSR 6 F
a rotational kickback reaction. This mode of Electrode gap: .020 in (0.5 mm)
activation is designed to stop the movement of
the chain in fractions of a second after activation
occurs.
– Inertially, by movement of the front hand guard
in reaction to the rotation of the chain saw. This
mode of activation also is designed to stop
movement of the chain in fractions of a second
after activation occurs. Note: activation requires
generation of sufficient inertial energy during the
kickback reaction.
– Manually, by release of the throttle trigger and
trigger lockout. This rear-handle activation of the
chain brake results in slower braking times-up to
a second or longer after activation depending on
the condition of the chain brake and activation
system.
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Technical Information 18.2010 Page 7
2.4 Fuel System 2.6 Cutting attachment
Carburetor
All position diaphragm carburetor 2.6.1 STIHL ROLLOMATIC® E and STIHL
ROLLOMATIC® ES guide bars
Standard setting with limiter cap on the Bar lengths (0.325" 16, 18, 20 in.
high speed screw: pitch): (40, 45, 50 cm)
Groove width: .063 in (1.6 mm)
Low speed screw L: Open 1 full turn
High speed screw H: Open 3/4 turn
2.6.2 STIHL OILOMATIC® chains
(no further than stop)
STIHL RAPID™ Micro™ Comfort 3 (RMC3)
Pitch: 0.325" (8.25 mm)
Drive link gauge: .063 in. or .050 in.
Basic setting without limiter cap on high speed (1.6 mm or 1.3 mm)
screw (in service shop)
Low speed screw L: Open 1 full turn
2.6.3 Chain sprocket
High speed screw H: Open 1 1/2 turns
7-tooth for 0.325"
Fuel mixture
See instruction manual.
Fuel tank capacity: 16.9 fl.oz (0.50 l)
2.5 Chain Lubrication
Oil pump: Speed-controlled pump.
Additional manual oil
flow control.
Oil tank capacity: 9.1 fl.oz (0.27 l)
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Page 8 Technical Information 18.2010
3. Servicing Accessories and
Special Tools
3.1 Special servicing tools
The following new special servicing tools are
required.
1 2 3
6
5
5902TI002 KN
Item Description Part No. Application
1 Press sleeve 1141 893 2400 Installing oil seal (ignition side)
2 Installing sleeve 1141 893 4600 Protecting the oil seal
3 Collar screw 5910 893 9600 Removing and installing collar nuts in sprocket cover
4 Screwdriver – 2mm 5910 890 2306 Adjusting carburetor (basic setting on high speed
hexagon tip screw with pre-assembled limiter cap)
5 Puller – 5910 890 4502 Pull off the limiter cap.
M3 left-hand thread
6 Puller 5910 890 4504 Removing flywheel
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Technical Information 18.2010 Page 9
Puller 5910 890 4504
The previous puller 1135 890 4500 has been
replaced with the new version 5910 890 4504.
The new puller features a longer base block, now
60 mm instead of 50 mm, with slots for the mounting
screws.
Only the new puller 5910 890 4504 will be available
from the factory in future.
3.2 Servicing Accessories
Description Part No. Application
Carburetor parts kit 1141 007 1006 Servicing the carburetor
Lubricating grease – 225 g 0781 120 1111 Oil seals, oil pump drive, sprocket bearing, chain tensioner
tube bearing and sliding points of throttle, brake and interlock
levers
3.3 Special Accessories for Users
Description Part No. Application
Cover plate kit 1141 007 1004 Prevents snow being sucked into machine in winter (used at
temperatures below –10°C, in powder and drifting snow)
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Page 10 Technical Information 18.2010
4. Service note
If the machine is started in the course of repairs, it is
essential to observe all country-specific safety
regulations and the safety precautions in the
instruction manual.
Run the chain saw only with the shroud mounted in
position – there is otherwise a risk of injury from the
fanwheel and a risk of engine damage due to
overheating.
5902TI012 KN
4.1 Chain sprocket cover with captive nuts
This sprocket cover can only be used on the . Clamp the hexagon of the special tool in a vise
MS 261. Retrofitting other models is not possible. so that the flange (arrow) of the collar nut is
The length and shape of the collar studs must be almost flush with the top of the sprocket cover.
matched to the sprocket cover with captive nuts.
. Drill away the flange (11 mm drill) – do not
Special tool 5910 893 9600 is available for replacing damage the shoulder in the sprocket cover.
the nuts in the service shop.
. Unscrew the old collar nuts from the special tool.
4.1.1 Drilling out the collar nut
4.1.2 Flaring the new collar nuts
. Remove the chain sprocket cover.
. Push the new collar nut (1) into position.
. Screw the long stud of the special tool into the
collar nut as far as stop.
1
5902TI011 KN
2
5902TI013 KN
. Screw the short stud of the special tool (1) into
the collar nut as far as stop.
. Clamp hexagon of special tool (2) in a vise – the
sprocket cover must not rest on the clamping
jaws.
. Tighten down the new collar nut firmly – this
flares the collar nut so it is captive in the
sprocket cover.
. Unscrew the special tool from the collar nut.
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Technical Information 18.2010 Page 11
4.2 Carburetor
On this carburetor the user can adjust the high
speed screw (H) within a range of about 3/4 turn.
1
4.2.1 New limiter caps
A new generation of limiter caps is being used for
the first time in the MS 261 to comply with different
national and international emission laws and
regulations. The new limiter cap features a zinc
5902TI015 KN
body and a polymer interior as a connecting element
with the adjusting screw.
The new puller has an M3 left-hand thread for
. Move the Master Control Lever™ to Stop 0.
removing the limiter cap.
. Insert a screwdriver in the recess (arrow) and
4.2.2 Removing the carburetor pry out the switch shaft (1).
. Remove the shroud and air filter. . Disconnect the short circuit wire.
. Set the Master Control Lever™ to choke
closed l.
3
1
5902TI016 KN
4
1
5902TI014 KN
. Unscrew the nuts (1) and remove the baffle (2).
. Swing the filter base (3) to the rear and out of
. Block the choke lever on the carburetor and the stud bolts.
push the Master Control Lever™ in the direction . Disconnect the filter base from the buffer (5) and
of Stop 0 – the rod (1) pops out of its seat. then swing it away to the left – buffer (4)
disconnects automatically.
. Pull off the carburetor.
The filter base hangs by the short circuit and ground
wires at the side of the machine during this
operation.
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Page 12 Technical Information 18.2010
4.2.3 Pull off the limiter cap. 4.2.4 Basic setting
The basic setting must be carried out on the
carburetor after servicing work or replacing the
3 adjusting screws.
2
. Check the air filter and clean or replace if
1 necessary.
. Check the spark arresting screen (not fitted in all
markets) in the muffler and clean or replace if
necessary.
5902TI017 KN
Use the following screwdrivers for the basic setting.
– Low speed screw L
Screwdriver 5910 890 2305 (for slotted screws)
. Screw the puller 5910 890 4502 (special tool)
about five turns counterclockwise (left-hand
– High speed screw H
thread) into the limiter cap.
Screwdriver 5910 890 2306 with 2mm hex tip
. Pull off the limiter cap.
. Use screwdriver (5910 890 2306) to unscrew . Carry out basic setting on the adjusting screws.
the high speed screw (H) with polymer segment. Starting with screws against their seats, adjust
counterclockwise.
Low speed screw L: Open 1 full turn
High speed screw H: Open 1 1/2 turns
Preassembling limiter cap on the high speed
screw
5902TI018 KN
. If the high speed screw (H) is re-used, remove
the polymer segment.
Do not re-install used limiter caps because they
are damaged during the removal process.
1
The service operations on the metering and pump
diaphragms, inlet needle, inlet control lever, gaskets
5902TI019 KN
and choke shutter are as before.
Do not disassemble the throttle shutter since the
factory setting will otherwise be upset and this may . Line up the new limiter cap (1) so that the
cause running problems. notch (arrow) points vertically upwards.
. Press the limiter cap (1) onto the high speed
screw (H) as far as first stop – almost flush with
the boss (arrow) – do not push fully home.
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Technical Information 18.2010 Page 13
. Install the carburetor. 4.2.5 Checking position of limiter cap
1 1
5902TI023 KN
5902TI022 KN
. Position the rod (1) in the opening. Push the . Notch (arrow) in limiter cap must point vertically
Master Control lever in direction of choke upwards.
closed l – the rod slips into its seat.
. Warm up the engine.
Adjustment
Adjust specified engine speeds within a tolerance 1
of +/- 200 rpm.
1. Adjust engine speed with idle speed screw
(LA) to 3,300 rpm
5902TI020 KN
2. Turn the low speed screw (L) clockwise or
counterclockwise to obtain the maximum
engine speed.
If the notch (arrow) in the limiter cap does not point
If this speed is higher than 3,700 rpm, abort the vertically upwards.
procedure and start again with step 1.
. Use a screwdriver to rotate the limiter cap (1)
counterclockwise as far as stop – the notch
3. Use the idle speed screw (LA) to set the (arrow) is now at the top.
engine speed again to 3,300 rpm
. Continue with "Securing limiter cap on the high
4. Set the engine speed to 2,800 rpm with the speed screw".
low speed screw (L).
5. Set the engine speed to 14,000 rpm with the
high speed screw (H).
If the setting is made too lean there is a risk of
engine damage as a result of lack of lubrication
and overheating.
6. Check position of limiter cap and secure the
limiter cap on the high speed screw.
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Page 14 Technical Information 18.2010
4.2.6 Securing limiter cap on the high speed 4.3 Fuel system – hose barb connectors
screw To guarantee the tightness of the fuel system:
. To avoid damaging hose barb connectors, pull
off and push on fuel hoses in line with the
connector by hand where possible – do not use
sharp-edged pliers, screwdrivers, etc. and do
not cut open fuel hoses with a knife or similar
tools.
. Do not re-use fuel hoses after removal. Always
replace with new hoses – fuel hoses may be
over-stretched during removal.
5902TI021 KN
. Fit new fuel hoses dry or with the aid of OH 723
press fluid – 0781 957 9000. Other press fluids
. Insert a drift (6mm diameter) through the are not approved and may result in damage to
opening (arrow) and use it to push the limiter the fuel hoses.
cap onto the adjusting screw as far as stop – the . Coat the ends of the hose and the connectors
limiter cap should be recessed about 0.08 in (2 with OH 723 press fluid and push the new hoses
mm) in the carburetor body when properly onto the hose barb connectors.
installed.
Note on OH 723 press fluid
4.2.7 Standard setting OH 723 press fluid produces a lubricating film which
simplifies assembly. The lubricant evaporates after
Use a standard carburetor screwdriver to carry out
a short period – the hose is then tight.
the standard setting with the limiter cap on the high
speed screw. Never use fuel, oil or grease as a lubricant for this
purpose. Fuel, oil and grease do not evaporate – the
. Shut off the engine.
hose may loosen or become detached.
. Check the air filter and clean or replace if
necessary.
. Check the spark arresting screen (not fitted in all
markets) in the muffler and clean or replace if
necessary.
. Turn the high speed screw (H) counterclockwise
as far as stop
(no more than 3/4 turn).
. Turn the low speed screw (L) slowly clockwise
as far as stop, then turn it back 1 full turn.
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Technical Information 18.2010 Page 15
4.4 Tightening torques
The tightening torques for the MS 261 are listed in Code Type of Repair MS 261
the STIHL MS 261 service manual. MS 261 C
1 Replace crankcase, crankcase 120
4.5 Service note gasket or re-seal crankcase.
Includes air leak test.
The STIHL MS 261 service manual is available for
servicing and repair procedures on the STIHL 3 Replace crankshaft main 110
MS 261. bearing(s). Includes air leak
test.
4.6 Serial number 4 Replace crankshaft seal(s). 50
Includes air leak test.
5 Perform engine air leak test. 30
6 Replace cylinder and/or piston. 60
Includes air leak test and repair
of components causing failure.
7 Replace ignition module or 30
flywheel. Includes stop circuit
test.
8 Replace fuel tank line, tank 25
0001TI007 KN
vent, or fuel pick-up body.
9 Replace intake manifold or 30
intake flange, including leak
The serial number is applied to the side of the test.
crankcase. 10 Repair or replace carburetor. 35
Includes fuel system testing.
4.7 Repair Times 11 Replace fuel tank housing. 25
The specified repair times assume that the work is 12 Replace oil pick-up/delivery 30
performed by trained personnel in a properly line. Includes oil output test.
equipped service workshop. 13 Replace oil pump and/or drive 30
Repair times are quoted in minutes. gear. Includes oil output test.
14 Replace rear handle frame or 25
handle housing.
15 Repair or replace rewind starte 20
16 Repair or replace clutch, clutch 20
shoes or clutch springs.
17 Repair chain break, including 35
check for proper function.
18 Replace muffler. 15
19 Replace air filter or filter 15
housing.
22 Repair or replace stop switch. 20
Includes circuit testing.
40 Miscellaneous repairs and 15
other repairs not listed.
45 Handling allowance only-no 10
labor.
50 No labor. 0
© ANDREAS STIHL AG & Co. KG, 2010 Technical Documentation
D1/MTK-bl
TI_18_2010_30_01_01.fm Extracted from the manufacturer's 2012 service catalogue. Most of these PDFs embed fonts with a shifted character map, so the text above was recovered rather than copied — read it as a faithful but imperfect transcription, and treat the page image above each block as the authority where the two disagree — the figures exist only there, because they are vector drawings that text extraction cannot keep.