STIHL MS 251
{
Instruction Manual
Notice d’emploi
G Instruction Manual
1 - 57
F Notice d’emploi
58 - 118
Contents
English
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
Original Instruction ManualPrinted on chlorine-free paper
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
Printing inks contain vegetable oils, paper can be recycled.
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
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
{
© ANDREAS STIHL AG & Co. KG, 2013
0458-737-8221-A. VA3.F13.
0000006313_004_GB
MS 251, MS 251 C
This instruction manual is protected by copyright. All rights reserved, especially the rights to reproduce, translate and process
with electronic systems.
1
English
Guide to Using this Manual
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.
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
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.
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. Nonobservance of the
instruction manual may
result in serious or even
fatal injury.
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.
-
-
2
MS 251, MS 251 C
English
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.
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.
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 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 safety glasses or a face shield and
hearing protection e.g. earplugs or ear
muffs.
Wear heavy-duty gloves.
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.
-
MS 251, MS 251 C
3
English
001BA087 LÄ
Fueling
Gasoline is an extremely
flammable fuel. Keep
clear of naked flames. Do
not spill any fuel – do not
smoke.
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 wellventilated 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.
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.
This reduces the risk of unit vibrations
causing the fuel cap to loosen or come
off and spill quantities of fuel.
Check for leakage. To
reduce the risk of serious
or fatal burn injuries, do
not start or run the engine
until leak is fixed.
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.
4
MS 251, MS 251 C
English
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.
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.
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.
MS 251, MS 251 C
5
English
001BA036 KN
001BA257 KN
001BA037 KN
A
Reactive Forces
The most common reactive forces that
occur during cutting are: kickback,
pushback and pull-in.
Dangers of kickback
Kickback can result in
serious or fatal injury.
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.
– 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)
Kickback occurs when the saw is
suddenly thrown up and back in an
uncontrolled arc towards the operator.
6
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 o f the lo cation 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.
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.
MS 251, MS 251 C
English
001BA038 KN
B
001BA082 KN
001BA033 KN
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, nai ls, 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
MS 251, MS 251 C
7
English
001BA088 LÄ
2
/
1
2
1 1
/
1
2
B
001BA040 KN
A
45°
45°
B
001BA146 KN
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.
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)
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.
Maintain a distance of at least 2 1/2 tree
lengths from the next felling site.
8
A Direction of fall
– Make the vertical cut first, then the
horizontal – but only if the wood is
sound
MS 251, MS 251 C
English
001BA153 KN
001BA143 KN
C
C
001BA150 KN
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.
MS 251, MS 251 C
9
English
001BA144 KN
D
D
001BA145 KN
E
E
001BA147 KN
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.
10
MS 251, MS 251 C
Large diameter trees: sectioning method
001BA148 KN
1
4
2
1
2
3
001BA179 KN
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
English
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 plungecutting 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.
MS 251, MS 251 C
11
English
1
001BA151 KN
2
1
001BA152 KN
2
001BA189 KN
– 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.
12
MS 251, MS 251 C
English
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
13
English
001BA248 KN
1
2
3
a
001BA244 KN
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.
Cutting Attachment
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.
14
MS 251, MS 251 C
English
533BA001 KN
1
2
001BA185 KN
001BA186 KN
143BA003 KN
3
1
1
2
4
001BA187 KN
Mounting the Bar and Chain
(side chain tensioner)
Removing the chain sprocket cover
N Unscrew the nut and remove the
chain sprocket cover.
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
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"
N Turn the screw (1)
counterclockwise until the tensioner
slide (2) butts against the left end of
the housing slot.
MS 251, MS 251 C
WARNING
Wear work gloves to protect your hands
from the sharp cutters.
N Fit the chain – start at the bar nose.
15
English
1
2
3
2310BA013 KN
1
2310BA014 KN
2310BA015 KN
2
1
3
2310BA016 KN
2
2310BA017 KN
001BA186 KN
1
181BA012 KN
Mounting the Bar and Chain
(quick chain tensioner)
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
Releasing the chain brake
N Remove screw (2)
N Pull hand guard towards the front
handle until it engages audibly –
chain brake is released
Fitting the saw chain
N Position tensioning gear (1) and
guide bar (3) relative to one another
N Remove and reverse tensioning
gear (1)
16
N Insert and tighten screw (2)
WARNING
Put on protective gloves – risk of injury
by the sharp cutters.
MS 251, MS 251 C
English
2
3
181BA013 KN
135BA011 KN
4
5
2310BA018 KN
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 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"
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
MS 251, MS 251 C
When fitting the chain sprocket cover,
the teeth of the adjusting wheel and the
tensioning gear must mesh; if
necessary,
17
English
1
142BA063 KN
1
2
001BA112 KN
142BA064 KN
Tensioning the Saw Chain
(side chain tensioner)
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".
Tensioning the Saw Chain
(quick chain tensioner)
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".
Checking Chain Tension
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".
18
MS 251, MS 251 C
English
Fuel
This engine is certified to operate on
unleaded gasoline and with the mix ratio
50:1.
Your engine requires a mixture of highquality premium gasoline and highquality two-stroke air-cooled engine oil.
Use premium branded unleaded
gasoline with a minimum octane rating
of 89 (R+M)/2.
Note: Models equipped with a catalytic
converter require unleaded gasoline. A
few tankfuls of leaded gasoline can
reduce the efficiency of the catalytic
converter by more than 50%.
Fuel with a lower octane rating may
result in preignition (causing "pinging")
which is accompanied by an increase in
engine temperature. This, in turn,
increases the risk of the piston seizure
and damage to the engine.
The chemical composition of the fuel is
also important. Some fuel additives not
only detrimentally affect elastomers
(carburetor diaphragms, oil seals, fuel
lines etc.), but magnesium castings as
well. This could cause running problems
or even damage the engine. For this
reason it is essential that you use only
high-quality fuels!
Fuels with different percentages of
ethanol are being offered. Ethanol can
affect the running behaviour of the
engine and increase the risk of lean
seizure.
Gasoline with an ethanol content of
more than 10% can cause running
problems and major damage in engines
with a manually adjustable carburetor
and should not be used in such engines.
Engines equipped with M-Tronic can be
run on gasoline with an ethanol content
of up to 25% (E25).
Use only STIHL two-stroke engine oil or
equivalent high-quality two-stroke aircooled engine oils for mixing.
We recommend STIHL 50:1 two-stroke
engine oil since it is specially formulated
for use in STIHL engines.
Do not use BIA or TCW (two-stroke
water cooled) mix oils!
Use only STIHL 50:1 heavy-duty engine
oil or an equivalent quality two-stroke
engine oil for the fuel mix in models
equipped with a catalytic converter.
Take care when handling gasoline.
Avoid direct contact with the skin and
avoid inhaling fuel vapour.
The canister should be kept tightly
closed in order to avoid any moisture
getting into the mixture.
The fuel tank and the canister in which
fuel mix is stored should be cleaned
from time to time.
Fuel mix ratio
Only mix sufficient fuel for a few days
work, not to exceed 3 months of storage.
Store in approved safety fuel-canisters
only. When mixing, pour oil into the
canister first, and then add gasoline.
Examples
Gasoline Oil (STIHL 50:1 or equiva
lent high-quality oils)
liters liters (ml)
1 0.02 (20)
5 0.10 (100)
10 0.20 (200)
15 0.30 (300)
20 0.40 (400)
25 0.50 (500)
Dispose of empty mixing-oil canisters
only at authorized disposal locations.
-
MS 251, MS 251 C
19
English
001BA229 KN
001BA240 KN
001BA218 KN
001BA219 KN
001BA224 KN
001BA220 KN
Fueling
Preparing the machine
N Before fueling, clean the cap and
the area around it to ensure that no
dirt falls into the fuel tank
N Always position the machine so that
the cap is facing upwards
Tank cap markings
Tank caps and fuel tanks may be
marked in different ways
Depending on the version, your machine
may be equipped with a tank cap and
fuel tank with or without symbols.
Left: Tank cap without symbols
Right: Tank cap with markings and
symbols on cap and tank
Tank cap without symbols
Opening
N Swing the grip to the upright
position.
N Remove the cap.
Filling up with fuel
Take care not to spill fuel while fueling
and do not overfill the tank.
STIHL recommends you use the STIHL
filler nozzle for fuel (special accessory).
N Fill up with fuel.
Closing
Grip must be vertical:
N Fit the cap – positioning marks on
tank cap and filler neck must be in
alignment.
N Press the cap down as far as stop.
20
N Rotate the tank cap about a quarter
turn counterclockwise.
MS 251, MS 251 C
English
001BA221 KN
001BA222 KN
001BA223 KN
001BA225 KN
001BA227 KN
001BA226 KN
001BA236 KN
N While holding the cap depressed,
turn it clockwise until it engages in
position.
N Fold the grip flush with the top of the
cap.
Checking security of cap
– The lug on the grip must fully
engage the recess (arrow).
N Grip the cap – it is properly locked if
it cannot be turned or removed.
If the cap can be turned or removed
Bottom of cap is twisted in relation to
top:
Left: Bottom of cap twisted
Right: Bottom of cap correctly
positioned
N Place the cap on the opening and
rotate it counterclockwise until it
engages the filler neck.
N Continue rotating the cap
counterclockwise (about a quarter
turn) – this causes the bottom of the
cap to be turned to the correct
position.
N Turn and lock the cap clockwise –
see sections on "Closing" and
"Checking security of cap".
Tank cap with markings and symbols
Opening
N Raise the grip until it is upright.
MS 251, MS 251 C
21
English
001BA232 KN
001BA234 KN
001BA237 KN
001BA234 KN
001BA233 KN
001BA231 KN
001BA235 KN
001BA241 KN
Closing
N Turn the cap counterclockwise
(about a quarter turn).
Marks on tank cap and fuel tank must
line up.
N Remove the cap.
Filling up with fuel
Take care not to spill fuel while fueling
and do not overfill the tank.
STIHL recommends you use the STIHL
filler nozzle for fuel (special accessory).
N Fill up with fuel.
Grip must be vertical:
N Fit the cap – marks on tank cap and
fuel tank must line up.
N Press the cap down as far as stop.
N While holding the cap depressed,
turn it clockwise until it engages in
position.
The marks on the tank cap and fuel tank
are then in alignment.
N Fold the grip down so that it is flush
with the top of the cap.
Tank cap is locked.
If the tank cap cannot be locked in the
fuel tank opening
Bottom of cap is twisted in relation to
top.
N Remove the cap from the fuel tank
and check it from above.
22
MS 251, MS 251 C
Left: Bottom of cap is twisted –
1
001BA238 KN
001BA239 KN
001BA158 KN
inner mark (1) in line with
outer mark.
Right: Bottom of cap in correct posi
tion – inner mark is under the
grip. It is not in line with the
outer mark.
N Place the cap on the opening and
rotate it counterclockwise until it
engages the filler neck.
N Continue rotating the cap
counterclockwise (about a quarter
turn) – this causes the bottom of the
cap to be turned to the correct
position.
N Turn the cap clockwise and lock it in
position – see section on "Closing".
Chain Lubricant Filling Chain Oil Tank
For automatic and reliable lubrication of
the chain and guide bar – use only an
environmentally compatible quality
chain and bar lubricant. Rapidly
biodegradable STIHL Bioplus is
recommended.
NOTICE
Biological chain oil must be resistant to
-
aging (e.g. STIHL Bioplus) since it will
otherwise quickly turn to resin. This
results in hard deposits that are difficult
to remove, especially in the area of the
chain drive and chain. It may even cause
the oil pump to seize.
The service life of the chain and guide
bar depends on the quality of the
lubricant. It is therefore essential to use
only a specially formulated chain
lubricant.
WARNING
Do not use waste oil. Renewed contact
with waste oil can cause skin cancer.
Moreover, waste oil is environmentally
harmful.
NOTICE
Waste oil does not have the necessary
lubricating properties and is unsuitable
for chain lubrication.
Preparations
N Thoroughly clean the oil filler cap
and the area around it to ensure that
no dirt falls into the tank.
N Position the machine so that the
filler cap is facing up.
N Open the filler cap.
Fill up with chain oil.
N Refill the chain oil tank every time
you refuel.
Take care not to spill chain oil while
refilling and do not overfill the tank.
STIHL recommends you use the STIHL
filler nozzle for chain oil (special
accessory).
N Close the filler cap.
There must still be a small amount of oil
in the oil tank when the fuel tank is
empty.
English
MS 251, MS 251 C
23
English
143BA024 KN
143BA011 KN
If the oil level in the tank does not go
down, the reason may be a fault in the oil
supply system: Check chain lubrication,
clean the oilways, contact your dealer
for assistance if necessary STIHL
recommends that you have servicing
and repair work carried out exclusively
by an authorized STIHL servicing
dealer.
Checking Chain Lubrication
The saw chain must always throw off a
small amount of oil.
NOTICE
Never operate your saw without chain
lubrication. If the chain runs dry, the
whole cutting attachment will be
irretrievably damaged within a very short
time. Always check chain lubrication and
the oil level in the tank before starting
work.
Every new chain has to be broken in for
about 2 to 3 minutes.
After breaking in the chain, check chain
tension and adjust if necessary – see
"Checking Chain Tension".
Chain Brake
Locking the chain
– in an emergency
– when starting
– at idling speed
The chain brake is activated by pushing
the hand guard toward the bar nose with
your left hand – or by inertia in certain
kickback situations: The chain is
stopped and locked.
24
MS 251, MS 251 C
English
143BA012 KN
2310BA000 KN
2310BA001 KN
Releasing the chain brake
N Pull the hand guard back toward the
front handle,
NOTICE
Always disengage chain brake before
accelerating the engine (except when
checking its operation) and before
starting cutting work.
High revs with the chain brake engaged
(chain locked) will quickly damage the
powerhead and chain drive (clutch,
chain brake).
The chain brake is also activated by the
inertia of the front hand guard if the
kickback force of the saw is high
enough: The hand guard is accelerated
toward the bar nose – even if your left
hand is not behind the hand guard, e.g.
during felling cut.
The chain brake will operate only if the
hand guard has not been modified in any
way.
Check operation of the chain brake
Before starting work: Run engine at idle
speed, engage the chain brake (push
hand guard toward bar nose) and open
the throttle wide for no more than
3 seconds – the chain must not rotate.
The hand guard must be free from dirt
and move freely.
Chain brake maintenance
The chain brake is subject to normal
wear. It is necessary to have it serviced
and maintained regularly by trained
personnel. STIHL recommends that you
have servicing and repair work carried
out exclusively by an authorized STIHL
servicing dealer. Maintain the following
servicing intervals:
Full-time usage: every 3
months
Part-time usage: every 6
months
Occasional usage: every 12
months
Winter Operation
Pre-heating carburetor
N Remove the shroud – see "Shroud"
At temperatures below +10 °C
N Using a screwdriver, pry the shutter
out of the s (summer operation)
position
N Place the shutter with the opening in
the direction of the chain saw in
the r position (winter operation) –
shutter must audibly snap into place
N Fit the shroud – see "Shroud"
MS 251, MS 251 C
25
English
STOP
0
001BA140 KN
Heated air is now drawn in from around
the cylinder and circulates around the
carburetor – this helps prevent
carburetor icing.
At temperatures above +20 °C
N Ensure that the shutter is always
returned to position s (summer
operation), otherwise the engine
may malfunction due to overheating
At temperatures below -10 °C
N if the chain saw is extremely cold
(frost formation) – after starting,
bring the engine up to operating
temperature at increased idle speed
(disengage chain brake!)
In case of erratic idling behavior or poor
acceleration
N Turn the low speed screw (L)
1/4 turn counterclockwise
Whenever the low speed screw (L) has
been adjusted, it is usually also
necessary to adjust the idle speed
adjusting screw (LA), see "Setting the
carburetor".
Air filter system
N Retrofit new air filter if necessary –
see "Air filter system"
Starting / Stopping the
Engine
Versions with Easy2Start
WARNING
This machine is extremely simple and
easy to start, even for children.
To reduce the risk of serious or fatal
injury:
– do not allow children or other
unauthorized persons to attempt to
start or otherwise use the machine
– never allow children or
unauthorized persons access to the
machine
– never leave the machine
unattended while working or during
work breaks
– after work, store in a safe, secure
location out of the reach of children
and other unauthorized persons
Positions of Master Control lever
Stop 0 – engine off – the ignition is
switched off
Normal run position (F) – engine runs or
can fire.
Starting throttle (n) – this position is
used to start a warm engine. The Master
Control lever moves to the normal run
position as soon as the throttle trigger is
squeezed.
Choke shutter closed (l) – this position
is used to start a cold engine.
Setting the Master Control Lever
26
To move the Master Control lever from
the normal run position (F) to choke
closed (l), press down the throttle
trigger lockout and squeeze the throttle
MS 251, MS 251 C
English
2310BA008 KN
trigger at the same time and hold them in
that position – now set the Master
Control lever.
To select the starting throttle
position (n), move the Master Control
lever to choke closed (l) first, then
push it into the starting throttle
position (n).
The Master Control lever must be in the
choke closed position (l) for the
changeover to the starting throttle
position (n).
The Master Control lever moves from
the starting throttle position (n) to the
run position (F) when you press down
the throttle trigger lockout and blip the
throttle trigger at the same time.
To switch off the engine, move the
Master Control lever to Stop (0).
Choke shutter closed (l)
– if the engine is cold
– If the engine stalls when you open
the throttle after starting.
– If the fuel tank was run until empty
(engine stopped).
Starting throttle position (n)
– If the engine is warm, i.e. if it has
been running for about one minute.
– when the engine begins to fire.
– after clearing a flooded combustion
chamber.
Fuel Pump
Press the fuel pump bulb several times –
even if the bulb is already filled with fuel:
– When starting for the first time.
– If the fuel tank was run until empty
(engine stopped).
Holding the Saw
There are two ways of holding the saw
when starting.
On the ground
N Place your saw on the ground.
Make sure you have a firm footing –
check that the chain is not touching
any object or the ground.
N Hold the saw firmly on the ground
with your left hand on the front
handle – your thumb should be
under the handle.
N Put your right foot into the rear
handle and press down.
MS 251, MS 251 C
27
English
2310BA009 KN
231BA010 KN
Between knees or thighs
N Hold the rear handle tightly between
your legs, just above the knees.
N Hold the front handle firmly with
your left hand – your thumb should
be under the handle.
Cranking
Standard versions
N Pull the starter grip slowly with your
right hand until you feel it engage –
and then give it a brisk strong pull
and push down the front handle at
the same time. Do not pull out the
starter rope to full length – it might
otherwise break. Do not let the
starter grip snap back. Guide it
slowly back into the housing so that
the starter rope can rewind properly.
Machines without additional manual fuel
pump: If the engine is new or after a long
out-of-service period, it may be
necessary to pull the starter rope several
times to prime the fuel system.
Versions with Easy2Start
The Easy2Start stores the energy
required to start the saw. For this reason
there may be a delay of a few seconds
between cranking the engine and it
actually starting.
There are two ways of starting machines
with Easy2Start:
N Hold the starter grip with your right
hand and pull it out slowly and
steadily – or – hold the starter grip
with your right hand and give it
several short pulls, using only a
short length of rope for each pull.
N Push down the handle while
cranking. Do not pull out the rope to
its full length – it might otherwise
break.
N Do not let the starter grip snap back.
Guide it slowly back into the housing
so that the starter rope can rewind
properly.
Starting the saw
WARNING
Bystanders must be well clear of the
general work area of the saw.
N Observe safety precautions.
28
MS 251, MS 251 C
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