STIHL MS 251 Manuel utilisateur

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STIHL MS 251

Instruction Manual

Notice d’emploi

G Instruction Manual

1 - 57

F Notice d’emploi

58 - 118

Original Instruction ManualPrinted on chlorine-free paper

Printing inks contain vegetable oils, paper can be recycled.

0458-737-8221-A. VA3.F13.

0000006313_004_GB

MS 251, MS 251 C

English

1

{

with electronic systems.

Contents

Dear Customer,

Thank you for choosing a quality

engineered STIHL product.

It has been built using modern

production techniques and

comprehensive quality assurance.

Every effort has been made to ensure

your satisfaction and troublefree use of

the product.

Please contact your dealer or our sales

company if you have any queries

concerning this product.

Your

Dr. Nikolas Stihl

Guide to Using this Manual 2

Safety Precautions and Working

Techniques 2

Cutting Attachment 14

Mounting the Bar and Chain (side

chain tensioner) 15

Mounting the Bar and Chain (quick

chain tensioner) 16

Tensioning the Saw Chain (side

chain tensioner) 18

Tensioning the Saw Chain (quick

chain tensioner) 18

Checking Chain Tension 18

Fuel 19

Fueling 20

Chain Lubricant 23

Filling Chain Oil Tank 23

Checking Chain Lubrication 24

Chain Brake 24

Winter Operation 25

Starting / Stopping the Engine 26

Operating Instructions 30

Taking Care of the Guide Bar 31

Shroud 32

Air Filter System 32

Cleaning the Air Filter 33

Engine Management 33

Adjusting the Carburetor 34

Spark Arresting Screen in Muffler 35

Spark Plug 35

Replacing the Starter Rope and

Rewind Spring 36

Storing the Machine 39

Checking and Replacing the Chain

Sprocket 40

Maintaining and Sharpening the

Saw Chain 41

Maintenance and Care 45

Main Parts 47

Specifications 49

Special Accessories 50

Ordering Spare Parts 50

Maintenance and Repairs 51

Disposal 51

Important Safety Instructions 51

Key to Symbols 53

STIHL Limited Emission Control

Warranty Statement 54

CSA Standard 56

MS 251, MS 251 C

English

2

Pictograms

Pictograms that appear on the machine

are explained in this Instruction Manual.

Depending on the machine and

equipment version, the following

pictograms may appear on the machine.

Symbols in text

WARNING

Warning where there is a risk of an

accident or personal injury or serious

damage to property.

NOTICE

Caution where there is a risk of

damaging the machine or its individual

components.

Engineering improvements

STIHL's philosophy is to continually

improve all of its products. For this

reason we may modify the design,

engineering and appearance of our

products periodically.

Therefore, some changes, modifications

and improvements may not be covered

in this manual.

Observe all application local safety

regulations, standards and ordinances.

If you have not used this type of power

tool before: Have your dealer or other

experienced user show you how to

operate your power tool or attend a

special course in its operation.

Minors should never be allowed to use a

power tool.

Keep bystanders, especially children,

and animals away from the work area.

When the power tool is not in use, shut it

off so that it does not endanger others.

Secure it against unauthorized use.

The user is responsible for avoiding

injury to third parties or damage to their

property.

Guide to Using this Manual

Fuel tank; fuel mixture of

gasoline and engine oil

Tank for chain oil; chain

oil

Engage and release

chain brake

Coasting brake

Direction of chain travel

Ematic; chain oil flow

adjustment

Tension saw chain

Intake air baffle: winter

operation

Intake air baffle: summer

operation

Handle heating

Actuate decompression

valve

Actuate manual fuel

pump

Safety Precautions and

Working Techniques

Because a chain saw is a

high-speed wood-cutting

tool with very sharp cut

-

ters, some special safety

precautions must be

observed in addition to

those that generally apply

when working with an axe

or hand saw.

It is important that you

read the instruction man

-

ual before first use and

keep it in a safe place for

future reference. Non-

observance of the

instruction manual may

result in serious or even

fatal injury.

MS 251, MS 251 C

English

3

Do not lend or rent your power tool

without the instruction manual. Be sure

that anyone using it understands the

information contained in this manual.

The use of noise emitting power tools

may be restricted to certain times by

national or local regulations.

To operate the power tool you must be

rested, in good physical condition and

mental health. If you have any condition

that might be aggravated by strenuous

work, check with your doctor before

operating a power tool.

Persons with pacemakers only: The

ignition system of your power tool

produces an electromagnetic field of a

very low intensity. This field may

interfere with some pacemakers. STIHL

recommends that persons with

pacemakers consult their physician and

the pacemaker manufacturer to reduce

any health risk.

Do not operate the power tool if you are

under the influence of any substance

(drugs, alcohol) which might impair

vision, dexterity or judgment.

To reduce the risk of accidents or injury,

put off the work in poor weather

conditions (rain, snow, ice, wind).

Only cut wood or wooden objects.

Do not use your power tool for any other

purpose because of the increased risk of

accidents.

Only use tools, guide bars, chains, chain

sprockets and accessories that are

explicitly approved for this power tool

model by STIHL or are technically

identical. If you have any questions in

this respect, consult a servicing dealer.

Use only high quality parts and

accessories in order to avoid the risk of

accidents and damage to the machine.

STIHL recommends the use of STIHL

original tools, guide bars, chains, chain

sprockets and accessories. They are

specifically designed to match the

product and meet your performance

requirements.

Never attempt to modify your power tool

in any way since this may increase the

risk of personal injury. STIHL excludes

all liability for personal injury and

damage to property caused while using

unauthorized attachments.

Do not use a pressure washer to clean

the unit. The solid jet of water may

damage parts of the unit.

Clothing and Equipment

Wear proper protective clothing and

equipment.

Avoid clothing that could get caught on

branches or brush or moving parts of the

machine. Do not wear a scarf, necktie or

jewelry. Tie up and confine long hair

(e.g. with a hair net, cap, hard hat, etc.).

Wear safety glasses or a face shield and

hearing protection e.g. earplugs or ear

muffs.

STIHL offers a comprehensive range of

personal protective clothing and

equipment.

Transporting the Chainsaw

Always engage the chain brake and fit

the chain guard (scabbard) – even when

you carry the saw for short distances.

Also stop the engine before carrying the

saw longer distances (more than

about 50 m).

Always carry the saw by the front handle

(handlebar) – with the hot muffler away

from your body – the guide bar must

point to the rear. To avoid serious burn

injuries, avoid touching hot parts of the

machine, especially the surface of the

muffler.

In vehicles: Properly secure your power

tool to prevent turnover, fuel spillage and

damage.

Clothing must be sturdy

but allow complete free

-

dom of movement. Wear

snug-fitting clothing with

cut retardant inserts – an

overall and jacket combi

-

nation, do not wear a

work coat.

Wear steel-toedsafety

boots with cut retardant

inserts and non-slip

soles.

Wear a safety hard hat

where there is a danger

of head injuries from fall

-

ing objects.

Wear heavy-duty gloves.

MS 251, MS 251 C

English

4

Fueling

Always shut off the engine before

refueling.

Do not fuel a hot engine – fuel may spill

and cause a fire.

Open the fuel cap carefully to allow any

pressure build-up in the tank to release

slowly and avoid fuel spillage.

Fuel your power tool only in well-

ventilated areas. If you spill fuel, wipe

the machine immediately – if fuel gets on

your clothing, change immediately.

Your power tool comes standard with

either a screw-type or bayonet-type fuel

cap.

This reduces the risk of unit vibrations

causing the fuel cap to loosen or come

off and spill quantities of fuel.

Before Starting

Check that your power tool is properly

assembled and in good condition – refer

to appropriate chapters in the instruction

manual.

– Check operation of chain brake,

front hand guard

– Correctly mounted guide bar

– Correctly tensioned chain

– Smooth action of throttle trigger and

throttle trigger lockout – throttle

trigger must return automatically to

idle position.

– Master Control lever / stop switch

must move easily to STOP or 0

– Check that the spark plug boot is

secure – a loose boot may cause

arcing that could ignite combustible

fumes and cause a fire.

– Never attempt to modify the controls

or safety devices in any way.

– Keep the handles dry and clean –

free from oil and pitch – for safe

control of the chain saw.

To reduce the risk of personal injury, do

not operate your saw if it is damaged or

not properly assembled.

Start the engine.

Start the engine at least 3 meters from

the fueling spot, outdoors only.

Place the unit on firm ground in an open

area. Make sure you have good balance

and secure footing. Hold the unit

securely. The cutting attachment must

be clear of the ground and all other

obstructions because it may begin to run

when the engine starts.

Your chain saw is designed to be

operated by one person only. Do not

allow other persons in the work area –

even when starting.

To reduce risk of chain rotation and

personal injury, lock the chain with the

chain brake before starting.

Do not drop start the power tool – start

the engine as described in the

instruction manual.

Do not attempt to start the saw when the

saw chain is in a cut.

Holding and Controlling the Power Tool

Always hold your saw firmly with both

hands: Right hand on the rear handle,

even if you are left-handed. To ensure

safe control, wrap your fingers tightly

around both handles.

Gasoline is an extremely

flammable fuel. Keep

clear of naked flames. Do

not spill any fuel – do not

smoke.

After fueling, tighten

down the screw-type fuel

cap as securely as

possible.

Insert the fuel cap with

hinged grip (bayonet-type

cap) correctly in the

opening, turn it clockwise

as far as stop and fold the

grip down.

Check for leakage. To

reduce the risk of serious

or fatal burn injuries, do

not start or run the engine

until leak is fixed.

001BA087 LÄ

MS 251, MS 251 C

English

5

During Operation

Make sure you always have good

balance and secure footing.

In the event of impending danger or in

an emergency, switch off the engine

immediately by moving the Master

Control lever / stop switch to STOP or 0.

Your power tool is designed to be

operated by one person only. Do not

allow other persons in the work area.

Never leave a running power tool

unattended.

When the engine is running: Note that

the chain continues to rotate for a short

period after you let go of the throttle

trigger (flywheel effect).

Take special care in slippery conditions

– damp, snow, ice, on slopes, uneven

ground and freshly debarked logs.

Watch out for obstacles such as tree

stumps, roots and ditches which could

cause you to trip or stumble.

Do not work alone – keep within calling

distance of others in case help is

needed.

Be particularly alert and cautious when

wearing hearing protection because

your ability to hear warnings (shouts,

alarms, etc.) is restricted.

To reduce the risk of accidents, take a

break in good time to avoid tiredness or

exhaustion

To reduce risk of fire, keep hot exhaust

gases and hot muffler away from easily

combustible materials (e.g. wood chips,

bark, dry grass, fuel). Mufflers with a

catalytic converter can become

particularly hot.

To reduce the risk of serious or fatal

injury from breathing toxic fumes,

ensure proper ventilation when working

in trenches, hollows or other confined

locations.

To reduce the risk of accidents, stop

work immediately in the event of

nausea, headache, visual disturbances

(e.g. reduced field of vision), problems

with hearing, dizziness, deterioration in

ability to concentrate. Apart from other

possibilities, these symptoms may be

caused by an excessively high

concentration of exhaust gases in the

work area.

The dusts (e.g. sawdust), vapor and

smoke produced during operation may

be dangerous to health. If dust levels are

very high, wear a suitable respirator.

Check the saw chain at regular short

intervals during operation or

immediately if there is a noticeable

change in cutting behavior:

– Shut off the engine and wait until the

chain comes to a complete

standstill.

– Check condition and proper

mounting.

– Check sharpness.

Do not touch the chain while the engine

is running. If the chain becomes jammed

by an obstruction, switch off the engine

immediately before attempting to

remove the obstruction – risk of injury.

To reduce the risk of injury, shut off the

engine before changing the saw chain.

To reduce the risk of fire, do not smoke

while operating or standing near your

power tool. Note that combustible fuel

vapor may escape from the fuel system.

If your power tool is subjected to

unusually high loads for which it was not

designed (e.g. heavy impact or a fall),

always check that it is in good condition

before continuing work – see also

"Before Starting". Check the fuel system

in particular for leaks and make sure the

safety devices are working properly. Do

not continue operating your power tool if

it is damaged. In case of doubt, have the

unit checked by your servicing dealer.

Make sure the idle speed setting is

correct. The chain must not run when

the engine is idling with the throttle

trigger released. Check and correct the

idle speed setting regularly. If the chain

continues to rotate when the engine is

idling, have your dealer make proper

adjustments or repairs.

Your power tool produces

toxic exhaust fumes as

soon as the engine is

running. These fumes

may be colorless and

odorless and contain

unburned hydrocarbons

and benzol. Never run

the engine indoors or in

poorly ventilated loca

-

tions, even if your model

is equipped with a cata

-

lytic converter.

MS 251, MS 251 C

English

6

Reactive Forces

The most common reactive forces that

occur during cutting are: kickback,

pushback and pull-in.

Dangers of kickback

Kickback occurs when the saw is

suddenly thrown up and back in an

uncontrolled arc towards the operator.

Kickback occurs, e.g.

– when the upper quadrant of the bar

nose unintentionally contacts wood

or another solid object, e.g. when

another limb is touched accidentally

during limbing.

– when the chain at the nose of the

guide bar is pinched in the cut.

QuickStop chain brake:

This device reduces the risk of injury in

certain situations – it cannot prevent

kickback. If activated, the brake stops

the saw chain within a fraction of a

second –

for a description of this device refer to

chapter on "Chain Brake" in this manual.

To reduce the risk of kickback

– Work cautiously and avoid

situations which could cause

kickback.

– Hold the saw firmly with both hands

and maintain a secure grip.

– Always cut at full throttle.

– Be aware of the location of the guide

bar nose at all times.

– Do not cut with the bar nose.

– Take special care with small, tough

limbs, they may catch the chain.

– Never cut several limbs at once.

– Do not overreach.

– Never cut above shoulder height.

– Use extreme caution when re-

entering a previous cut.

– Do not attempt plunge cuts if you

are not experienced in this cutting

technique.

– Be alert for shifting of the log or

other forces that may cause the cut

to close and pinch the chain.

– Always cut with a correctly

sharpened, properly tensioned

chain – the depth gauge setting

must not be too large.

– Use a low kickback chain and a

narrow radius guide bar.

Pull-in (A)

Pull-in occurs when the chain on the

bottom of the bar is suddenly pinched,

caught or encounters a foreign object in

the wood. The reaction of the chain pulls

the saw forward – always hold the

spiked bumper securely against the tree

or limb.

Kickback can result in

serious or fatal injury.

001BA036 KN

001BA257 KN

001BA037 KN

A

MS 251, MS 251 C

English

7

Pushback (B)

Pushback occurs when the chain on the

top of the bar is suddenly pinched,

caught or encounters a foreign object in

the wood. The reaction of the chain

drives the saw straight back toward the

operator. To avoid pushback:

– Be alert to situations that may cause

the top of the guide bar to be

pinched

– Do not twist the guide bar in the cut.

Exercise extreme caution

– with leaners

– with trees that have fallen

unfavorably between other trees

and are under strain

– when working in blowdown areas.

Do not work with the chainsaw in such

circumstances. Use block and tackle,

cable winch or tractor.

Pull out exposed and cleared logs.

Select clear area for cutting.

Deadwood (dry, decayed or rotted

wood) represents a considerable risk

that is difficult to assess. Identifying the

extent of the dangers is complicated, if

not impossible. Use aids such as a cable

winch or tractor in such cases.

When felling in the vicinity of roads,

railways, power lines, etc., take extra

precautions. If necessary, inform the

police, utility company or railway

authority.

Cutting

Do not operate your saw with the

starting throttle lock engaged. Engine

speed cannot be controlled with the

throttle trigger in this position.

Work calmly and carefully – in daylight

conditions and only when visibility is

good. Ensure you do not endanger

others – stay alert at all times.

Use the shortest possible guide bar: The

chain, guide bar and chain sprocket

must match each other and your saw.

Position the saw so that your body is

clear of the cutting attachment.

Always pull the saw out of the cut with

the chain running.

Use your chain saw for cutting only. It is

not designed for prying or shoveling

away limbs, roots or other objects.

Do not underbuck freely hanging limbs.

To reduce the risk of injury, take special

care when cutting shattered wood

because of the risk of injury from slivers

being caught and thrown in your

direction.

Make sure your saw does not touch any

foreign materials: Stones, nails, etc. may

be flung off, damage the saw chain or

cause the saw to kick back

unexpectedly.

If on a slope, stand on the uphill side of

the log. Watch out for rolling logs.

When working at heights:

– Always use a lift bucket

– Never work on a ladder or in a tree

– Never work on an insecure support

– Do not work above shoulder height

– Never operate your power tool with

one hand

001BA038 KN

B

001BA082 KN

001BA033 KN

MS 251, MS 251 C

English

8

Begin cutting with the saw at full throttle

and engage the spiked bumper firmly in

the wood, and then continue cutting.

Never work without the spiked bumper

because the saw may pull you forwards

and off balance. Always engage the

spiked bumper securely in the tree or

limb.

Note when reaching the end of a cut that

the saw is no longer supported in the

kerf. You have to take the full weight of

the unit since it might otherwise go out of

control.

Felling

Do not attempt felling unless you have

been trained in the necessary

techniques. To reduce the risk of

accidents and injury, do not attempt

felling or limbing if you are not an

experienced chain saw user.

Observe all country-specific regulations

on felling techniques.

Check that there are no other persons in

the felling area – other than helpers.

Make sure no-one is endangered by the

falling tree – the noise of your engine

may drown any warning calls.

Maintain a distance of at least 2 1/2 tree

lengths from the next felling site.

Determine direction of fall and escape

paths

Select gap in stand into which you want

the tree to fall.

Pay special attention to the following

points:

– The natural lean of the tree

– Any unusually heavy limb structure,

damage

– The wind direction and speed – do

not fell in high winds

– Sloping ground

– Neighboring trees

– Snow load

– Soundness of tree – take special

care if trunk is damaged or in case

of deadwood (dry, decayed or rotted

wood)

A Direction of fall

B Escape paths

– Establish paths of escape for

everyone concerned – opposite to

direction of fall at about 45°.

– Remove all obstacles from escape

paths.

– Place all tools and equipment a safe

distance away from the tree, but not

on the escape paths.

– Always keep to the side of the falling

tree and only walk away along the

preplanned escape path.

– On steep slopes, plan escape

routes parallel to the slope.

– When walking away along the

escape path, watch out for falling

limbs and watch the top of the tree.

Preparing work area at base of tree

– First clear the tree base and work

area from interfering limbs and

brush to provide a secure footing.

– Clean lower portion of tree base

(e.g. with an axe) – sand, stones

and other foreign objects will dull the

saw chain.

– Make the vertical cut first, then the

horizontal – but only if the wood is

sound

001BA088 LÄ

2

/

1

2

1 1

/

1

2

B

001BA040 KN

A

45°

B

001BA146 KN

MS 251, MS 251 C

English

9

Making felling notch

When making the felling notch, make

use of the gunning sight on the shroud

and fan housing to check the planned

direction of fall.

Position your saw so that the gunning

sight points in exactly the direction you

want the tree to fall.

There are several approved methods for

making the felling notch – observe

country-specific regulations on felling

techniques.

The felling notch (C) determines the

direction of fall.

STIHL recommends the following

method:

N Make the horizontal cut – check the

direction of fall with the gunning

sight.

N Make angle cut at about 45°.

N Check the felling notch and correct it

if necessary.

Important:

– Felling notch at a right angle to the

planned direction of fall.

– As close to the ground as possible.

– Cut to a depth of about 1/5 to 1/3 of

the trunk diameter.

Sapwood cuts

Sapwood cuts in long-fibered softwood

help prevent sapwood splintering when

the tree falls. Make cuts at both sides of

the trunk at same height as bottom of

felling notch to a depth of about 1/10 of

trunk diameter. On large diameter trees,

cut to no more than width of guide bar.

Do not make sapwood cuts if wood is

diseased.

001BA153 KN

001BA143 KN

C

001BA150 KN

MS 251, MS 251 C

English

10

Felling

Shout a warning before starting the

felling cut.

N Make the felling cut (D) slightly

higher than bottom of the felling

notch.

– Cut horizontally.

– Leave approx. 1/10 of the tree

diameter uncut between the felling

cut and the felling notch. This is the

hinge.

Drive wedges into the felling cut in good

time. Use only wooden, aluminum or

plastic wedges. Never steel, which can

damage the chain and cause kickback.

The hinge (E) helps control the falling

tree.

– To reduce the risk of accidents, do

not cut through the hinge – you

could lose control of the direction of

fall.

– Leave a broader hinge on rotten

trees.

Shout a second warning immediately

before the tree falls.

Small diameter trees: simple fan cut

N Engage the spiked bumper behind

the hinge – pivot the saw around this

point - only as far as the hinge. The

spiked bumper rolls against the

trunk.

001BA144 KN

D

001BA145 KN

E

001BA147 KN

MS 251, MS 251 C

English

11

Large diameter trees: sectioning method

If the diameter of the tree is greater than

the length of the guide bar, use the

sectioning method.

1. First cut

Nose of guide bar should enter

wood just behind the hinge – hold

the saw horizontally and swing it as

far as possible, using the bumper

spike as a pivot – avoid

repositioning the saw more than

necessary.

2. When repositioning the saw for the

next cut, keep the guide bar fully

engaged in the kerf to keep the

felling cut straight – engage the

spiked bumper again, and so on.

3. Insert a wedge (3) in the cut.

4. Last cut: Engage the spiked bumper

as for the simple fan cut – do not cut

through the hinge.

Special cutting techniques

Plunge cuts and heartwood cuts require

special training and experience.

Plunge cutting

– For felling leaners

– For relieving cuts during bucking

– For DIY projects

N Use a low kickback chain and

exercise particular caution

1. Begin cut by applying the lower

portion of the guide bar nose – do

not use upper portion because of –

risk of kickback. Cut until depth of

kerf is twice the width of the guide

bar.

2. Swing saw slowly into plunge-

cutting position – take care because

of the risk of kickback or pushback.

3. Make the plunge cut very carefully.

Danger of pushback.

Heartwood cut

– If tree diameter is more than twice

the length of the guide bar.

– If a large portion of heartwood

remains uncut on large diameter

trees.

001BA148 KN

1

4

2

1

2

3

001BA179 KN

MS 251, MS 251 C

English

12

– On trees that are difficult to fell (oak,

beech), to prevent heartwood

splintering and maintain planned

direction of fall.

– On soft deciduous trees to relieve

tension in lying log and prevent

slivers in the center of the hinge

being torn out of the log.

N Make the plunge cut in the center of

the felling notch – there is a danger

of pushback at this point – then

swing the bar in the direction of the

arrow.

Limbing

Do not attempt limbing unless you have

been trained in the necessary

techniques. To reduce the risk of

accidents and injury, do not attempt

felling or limbing if you are not an

experienced chain saw user.

– Use a low kickback chain.

– Work with the saw supported

wherever possible.

– Do not stand on the log while

limbing it.

– Do not cut with the bar nose.

– Watch for limbs which are under

tension.

– Never cut several limbs at once.

When cutting small logs

– Use a sturdy and stable support –

sawhorse.

– Never hold the log with your leg or

foot.

– Never allow another person to hold

the log or help in any other way.

Lying or standing logs under tension

Always make cuts in the correct

sequence (first at the compression

side (1), then at the tension side (2), the

saw may otherwise pinch or kick back –

risk of injury.

N Make relieving cut at the

compression side (1)

N Make bucking cut at the tension

side (2)

Be wary of pushback when making

bucking cut from the bottom upwards

(underbuck).

NOTICE

Do not cut a lying log at a point where it

is touching the ground because the saw

chain will otherwise be damaged.

Ripping cut

Cutting technique in which the spiked

bumper is not used – risk of pull-in – start

the cut with the guide bar at the

shallowest possible angle – take extra

care since there is an increased danger

of kickback.

1

001BA151 KN

2

1

001BA152 KN

2

001BA189 KN

MS 251, MS 251 C

English

13

Vibrations

Prolonged use of the power tool may

result in vibration-induced circulation

problems in the hands (whitefinger

disease).

No general recommendation can be

given for the length of usage because it

depends on several factors.

The period of usage is prolonged by:

– Hand protection (wearing warm

gloves)

– Work breaks

The period of usage is shortened by:

– Any personal tendency to suffer

from poor circulation (symptoms:

frequently cold fingers, tingling

sensations).

– Low outside temperatures.

– The force with which the handles

are held (a tight grip restricts

circulation).

Continual and regular users should

monitor closely the condition of their

hands and fingers. If any of the above

symptoms appear (e.g. tingling

sensation in fingers), seek medical

advice.

Maintenance and Repairs

Service the machine regularly. Do not

attempt any maintenance or repair work

not described in the instruction manual.

Have all other work performed by a

servicing dealer.

STIHL recommends that you have

servicing and repair work carried out

exclusively by an authorized STIHL

servicing dealer. STIHL dealers are

regularly given the opportunity to attend

training courses and are supplied with

the necessary technical information.

Only use high-quality replacement parts

in order to avoid the risk of accidents

and damage to the machine. If you have

any questions in this respect, consult a

servicing dealer.

STIHL recommends the use of genuine

STIHL replacement parts. They are

specifically designed to match your

model and meet your performance

requirements.

To reduce the risk of injury, always shut

off the engine before carrying out any

maintenance or repairs or cleaning the

machine. – Exception: Carburetor and

idle speed adjustments.

Do not turn the engine over on the

starter with the spark plug boot or spark

plug removed unless the slide control /

stop switch is on STOP or 0 since there

is otherwise a risk of fire from

uncontained sparking.

To reduce the risk of fire, do not service

or store your machine near open flames.

Check the fuel filler cap for leaks at

regular intervals.

Use only a spark plug of the type

approved by STIHL and make sure it is

in good condition – see "Specifications".

Inspect the ignition lead (insulation in

good condition, secure connection).

Check the condition of the muffler.

To reduce the risk of fire and damage to

hearing, do not operate your machine if

the muffler is damaged or missing. –

Do not touch a hot muffler since burn

injury will result.

Vibration behavior is influenced by the

condition of the AV elements – check the

AV elements at regular intervals.

Check the chain catcher and replace it if

damaged.

Stop the Engine

– before checking chain tension.

– before retensioning the chain.

– before replacing the chain.

– before rectifying problems.

Observe sharpening instructions – keep

the chain and guide bar in good

condition at all times for safe and correct

handling of the saw. The chain must be

properly sharpened, tensioned and well

lubricated.

Always change the chain, guide bar and

sprocket in good time.

Check condition of clutch drum

periodically.

Store fuel and chain lubricant in properly

labelled, safety-type canisters only.

When handling gasoline, avoid direct

contact with the skin and avoid inhaling

fuel vapour – health risk.

To reduce the risk of injury, shut off the

engine immediately if the chain brake

malfunctions – contact your servicing

dealer – do not use your power tool until

the problem has been rectified (see

"Chain Brake").

MS 251, MS 251 C

English

14

Maintenance, replacement, or repair of

the emission control devices and

systems may be performed by any

nonroad engine repair establishment or

individual. However, if you make a

warranty claim for a component which

has not been serviced or maintained

properly or if nonapproved replacement

parts were used, STIHL may deny

coverage.

For any maintenance please refer to the

maintenance chart and to the warranty

statement near the end of the instruction

manual.

STIHL is the only manufacturer in the

industry to produce its own chain saws,

guide bars, saw chains and chain

sprockets.

A cutting attachment consists of the saw

chain, guide bar and chain sprocket.

The cutting attachment that comes

standard is designed to exactly match

the chain saw.

– The pitch (t) of the saw chain (1),

chain sprocket and the nose

sprocket of the Rollomatic guide bar

must match.

– The drive link gauge (2) of the saw

chain (1) must match the groove

width of the guide bar (3).

If non-matching components are used,

the cutting attachment may be damaged

beyond repair after a short period of

operation.

Chain Scabbard

Your saw comes standard with a chain

scabbard that matches the cutting

attachment.

If guide bars of different lengths are

mounted to the saw, always use a chain

scabbard of the correct length which

covers the complete guide bar.

The length of the matching guide bars is

marked on the side of the chain

scabbard.

Cutting Attachment

001BA248 KN

1

2

3

a

001BA244 KN

MS 251, MS 251 C

English

15

Removing the chain sprocket cover

N Unscrew the nut and remove the

chain sprocket cover.

N Turn the screw (1)

counterclockwise until the tensioner

slide (2) butts against the left end of

the housing slot.

Disengage the chain brake.

N Pull the hand guard towards the

front handle until there is an audible

click – the chain brake is

disengaged.

Fitting the chain

WARNING

Wear work gloves to protect your hands

from the sharp cutters.

N Fit the chain – start at the bar nose.

N Fit the guide bar over the studs (1) –

the cutting edges on the top of the

bar must point to the right.

N Engage the peg of the tensioner

slide in the locating hole (2) –- place

the chain over the sprocket (3) at

the same time.

N Turn the tensioning screw (4)

clockwise until there is very little

chain sag on the underside of the

bar – and the drive link tangs are

engaged in the bar groove.

N Refit the sprocket cover and screw

on the nut only fingertight.

N Go to chapter on "Tensioning the

Saw Chain"

Mounting the Bar and Chain

(side chain tensioner)

533BA001 KN

1

2

001BA185 KN

001BA186 KN

143BA003 KN

3

1

2

4

001BA187 KN

MS 251, MS 251 C

English

16

Removing the chain sprocket cover

N Swing grip (1) into position (until it

engages)

N Turn the wing nut (2) to the left until

it hangs loosely in the chain

sprocket cover (3)

N Remove chain sprocket cover (3)

Mounting the tensioning gear

N Remove and reverse tensioning

gear (1)

N Remove screw (2)

N Position tensioning gear (1) and

guide bar (3) relative to one another

N Insert and tighten screw (2)

Releasing the chain brake

N Pull hand guard towards the front

handle until it engages audibly –

chain brake is released

Fitting the saw chain

WARNING

Put on protective gloves – risk of injury

by the sharp cutters.

Mounting the Bar and Chain

(quick chain tensioner)

1

2

3

2310BA013 KN

1

2310BA014 KN

2310BA015 KN

2

1

3

2310BA016 KN

2

2310BA017 KN

001BA186 KN

1

181BA012 KN

MS 251, MS 251 C

English

17

N Fit the saw chain – starting at the

nose of the guide bar – pay attention

to the position of the tensioning gear

and the cutting edges

N Turn tensioning gear (1) to the right

as far as possible

N Turn the guide bar so that the

tensioning gear faces the user

N Place the saw chain on the chain

sprocket (2)

N Slide the guide bar over the collar

screw (3); the head of the rear collar

screw must protrude into the oblong

hole

N Guide the drive link into the bar

groove (see arrow) and turn the

tensioning gear to the left as far as

possible

N Fit chain sprocket cover, sliding the

guide lugs into the engine housing

openings

When fitting the chain sprocket cover,

the teeth of the adjusting wheel and the

tensioning gear must mesh; if

necessary,

N turn the adjusting wheel (4) a little

until the chain sprocket cover can

be slid completely against the

engine housing

N Swing grip (5) into position (until it

engages)

N Fit wing nut and tighten lightly

N Next step: see "Tensioning the Saw

Chain"

2

3

181BA013 KN

135BA011 KN

4

5

2310BA018 KN

MS 251, MS 251 C

English

18

Retensioning during cutting work:

N Switch off the engine.

N Loosen the nut.

N Hold the bar nose up.

N Use a screwdriver to turn the

tensioning screw (1) clockwise until

the chain fits snugly against the

underside of the bar.

N While still holding the bar nose up,

tighten down the nut firmly.

N Go to "Checking Chain Tension".

A new chain has to be retensioned more

often than one that has been in use for

some time.

N Check chain tension frequently –

see chapter on "Operating

Instructions".

Retensioning during cutting work:

N Shut off the engine.

N Pull out the hinged clip and loosen

the wingnut.

N Turn the adjusting wheel (1)

clockwise as far as stop.

N Tighten down the wingnut (2) firmly

by hand.

N Fold down the hinged clip.

N Go to "Checking Chain Tension"

A new chain has to be retensioned more

often than one that has been in use for

some time.

N Check chain tension frequently –

see chapter on "Operating

Instructions".

N Shut off the engine.

N Wear work gloves to protect your

hands.

N The chain must fit snugly against

the underside of the bar and it must

still be possible to pull the chain

along the bar by hand when the

chain brake is released.

N If necessary, retension the chain.

A new chain has to be retensioned more

often than one that has been in use for

some time.

N Check chain tension frequently –

see chapter on "Operating

Instructions".

Tensioning the Saw Chain

(side chain tensioner)

1

142BA063 KN

Tensioning the Saw Chain

(quick chain tensioner)

1

2

001BA112 KN

Checking Chain Tension

142BA064 KN

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STIHL MS 251 Manuel utilisateur

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