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Stihl MS 251 C-Q

Stihl MS 251 C-Q
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STIHL MS 251 C-Q
Instruction Manual
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Stihl MS 251 C-Q Specifications

General IconGeneral
Chain Pitch3/8"
Vibration Levels Left/Right3.9/3.9 m/s²
Bar Length40 cm
Oil Capacity0.2 l (6.8 oz)
Chain Gauge0.050"
Bar Lengths Available40 cm
EmissionsEPA Phase II compliant
Engine Type2-stroke gasoline
Displacement45.6 cc (2.78 cu in)
Power Output2.2 kW (3.0 bhp)

Summary

QuickStop Super Chain Brake System

Guide to Using this Manual

Pictograms

Explains symbols used on the machine and in the manual.

Safety Precautions

General

General safety regulations, local ordinances, and user responsibilities.

Symbols in text

Explains the meaning of WARNING and NOTICE symbols in the text.

Clothing and Equipment

Transport

Intended use

Accessories

Refuelling

Before Starting Work

During operation

Reactive Forces

Dangers of kickback

Explains how kickback occurs and its fatal consequences.

Switch off the engine

After finishing work

QuickStop chain brake

Reducing the risk of kickback

Working Techniques

Cutting

Instructions on safe and efficient cutting procedures.

When cutting small logs

Limbing

Lying or standing logs under tension

Ripping cut

Preparations for Felling

Determine direction of fall and escape path

Planning the tree fall direction and safe escape routes.

Preparing work area at base of tree

Felling Notch

Preparing felling notch

Steps to prepare the felling notch for directional cutting.

Making Felling Notch

Positioning the saw and sequence for making the felling notch.

Check direction of fall

Sapwood cuts

Basic Information on Felling Cut

Stump dimensions

Explains dimensions of stump cuts for felling.

Plunge cutting

Technique for cutting into the trunk with the guide bar nose.

Choosing Right Felling Cut

Felling wedges

Felling Cut with Stabilizing Strap (Normal Tree)

A) Small diameter trees

Felling cut procedure for trees smaller than guide bar length.

Felling Cut with Stabilizing Strap (Normal Tree)

B) Large diameter trees

Felling cut procedure for trees larger than guide bar length.

Felling Cut with Holding Strap (Leaner)

A) Small diameter trees

Felling cut procedure for leaners, small diameter.

B) Large diameter trees

Felling cut procedure for leaners, large diameter.

Cutting Attachment

Chain Scabbard

Mounting the Bar and Chain (quick chain tensioner)

Removing the chain sprocket cover

Steps to remove the chain sprocket cover.

Mounting the tensioning gear

Steps to mount the tensioning gear.

Releasing the chain brake

Fitting the saw chain

Tensioning the Saw Chain (quick chain tensioner)

Retensioning during cutting work

How to retension the saw chain while cutting.

Checking Chain Tension

Fuel

STIHL MotoMix

STIHL's ready-to-use fuel mix for optimal engine performance.

Mixing Fuel

Guidelines for mixing gasoline and two-stroke engine oil.

Gasoline

Specifications for using high-quality brand-name gasoline.

Engine oil

Recommendations for using high-quality two-stroke engine oil.

Mix Ratio

Recommended mix ratio for STIHL 50:1 two-stroke engine oil.

Storing Fuel

Proper storage guidelines for fuel and fuel mix.

Fueling

Preparing the machine

Steps to prepare the machine before fueling.

Tank cap markings

Explains different markings on tank caps and fuel tanks.

Opening

How to open the fuel tank cap.

Filling up with fuel

Closing

Checking security of cap

Tank cap with markings and symbols

Opening

How to open fuel caps with markings and symbols.

Closing

How to close fuel caps with markings and symbols.

Chain Lubricant

If the tank cap cannot be locked in the fuel tank opening

Troubleshooting steps if the fuel tank cap cannot be locked.

Filling Chain Oil Tank

Preparations

Steps to prepare for filling the chain oil tank.

Fill up with chain oil.

Instructions for filling the chain oil tank.

Checking Chain Lubrication

Chain Brake

Disengaging the coasting brake

How to disengage the coasting brake function.

Disengaging the chain brake

How to disengage the standard chain brake.

Chain brake is activated

Explains how the chain brake is activated.

Chain brake is activated by inertia

Explains inertia activation of the chain brake.

Checking operation of the coasting brake

Checking operation of the chain brake

Chain brake maintenance

Winter Operation

Pre-heating carburetor

Adjusting the carburetor for winter conditions to prevent icing.

At temperatures above +20 C

Recommendations for operation in warm temperatures.

At temperatures below -10 C

Recommendations for operation in very cold temperatures.

Air filter system

Information on retrofitting or checking the air filter system.

Starting Stopping the Engine

Positions of Master Control Lever

Explains the different positions of the Master Control Lever.

Setting the Master Control Lever

How to set the Master Control Lever for starting and stopping.

Fuel pump

How to use the manual fuel pump.

Holding the Saw

Describes how to hold the saw when starting.

On the ground

Between knees or thighs

Cranking

Standard versions

How to start the engine on standard models.

Versions with ErgoStart

Starting the Saw

Versions with manual fuel pump

Starting procedure for models with a manual fuel pump.

All models

General starting procedure applicable to all models.

When engine begins to fire

As soon as the engine runs

At very low outside temperatures

Stopping the engine

If the engine does not start

Operating Instructions

During the break-in period

Guidelines for operating the new machine during its initial period.

During work

General operating instructions and precautions during use.

Check chain tension frequently

Importance and frequency of checking chain tension.

Chain cold

How to check chain tension when the chain is cold.

Chain at operating temperature

How to check chain tension when the chain is warm.

After a long period of full-throttle operation

Procedure after extended full-throttle operation.

After finishing work

Steps to take after completing work.

Taking Care of the Guide Bar

Flip the bar - after each sharpening and each time the chain is changed

Recommendation to flip the guide bar to ensure even wear.

Shroud

Remove shroud

Steps for removing the shroud.

Refitting the shroud

Steps for refitting the shroud.

Air Filter System

Fleece filter

Description of the fleece filter for normal conditions.

HD2 filter

Description of the HD2 filter for extreme conditions.

Cleaning the Air Filter

Installing the air filter

Steps for installing the air filter.

Adjusting the Carburetor

Basic information

General information about the carburetor settings.

Standard setting

Factory default carburetor settings.

Engine stops when idling

Troubleshooting steps when the engine stops during idling.

Saw chain rotates at idle speed

Troubleshooting steps if the saw chain rotates at idle.

Speed erratic when idling; poor acceleration

Adjusting the carburetor for erratic idling or poor acceleration.

Correcting the carburetor setting for use at high altitudes

Adjusting carburetor for performance at high altitudes.

Spark Arresting Screen in Muffler

Spark Plug

Checking the Spark Plug

How to check the spark plug's condition and gap.

Removing the spark plug

Steps to remove the spark plug.

Installing the spark plug

Storing the Machine

Checking and Replacing the Chain Sprocket

Maintaining and Sharpening the Saw Chain

Sawing effortlessly with a properly sharpened saw chain

Benefits of a sharp saw chain for efficient cutting.

Chain pitch

Sharpening and side plate angles

A Sharpening angle

Recommended sharpening angle for STIHL saw chains.

B Side plate angle

How the side plate angle is achieved with specific tools.

File holder

To check the angles

Proper sharpening

Select sharpening tools in accordance with chain pitch

Choosing the correct sharpening tools based on chain pitch.

Clamp guide bar if necessary

Instructions for clamping the guide bar during sharpening.

Block saw chain - push the hand guard forward

How to block the saw chain for safe sharpening.

Sharpen frequently, removing little material

Advice on frequent sharpening with minimal material removal.

Depth gauge setting

Explanation of depth gauge function and setting.

Lowering the depth gauges

Rework the depth gauge so that it is flush with the file gauge

Sharpening tools (special accessories)

Maintenance and Care

Complete machine

Maintenance schedule for the entire machine.

Chain brake

Maintenance and checks for the chain brake.

Manual fuel pump (if present)

Maintenance for the manual fuel pump.

Fuel pick-up body filter in fuel tank

Maintenance of the fuel pick-up body and filter.

Fuel tank

Cleaning the fuel tank.

Lubricating oil tank

Cleaning the lubricating oil tank.

Chain lubrication

Checking and maintaining chain lubrication.

Saw chain

Maintenance for the saw chain, including tension and sharpening.

Guide bar

Maintenance for the guide bar, including cleaning and deburring.

Chain sprocket

Checking and cleaning the chain sprocket.

Air filter

Maintenance and replacement of the air filter.

Anti-vibration elements

Air intake on fan housing

Cylinder fins

Carburetor

Spark plug

All accessible screws, nuts and bolts (not adjusting screws)

Spark arresting screen in muffler

Chain catcher

Exhaust bore

Safety information label

Main Parts

Specifications

Engine

Technical specifications for the engine.

Ignition System

Technical specifications for the ignition system.

Fuel System

Technical specifications for the fuel system.

Chain Lubrication

Technical specifications for chain lubrication.

Weight

Weight specifications of the machine.

Chain sprocket

Specifications for the chain sprocket.

Cutting attachment

Specifications for cutting attachments like guide bars and chains.

Noise and Vibration Data

Data on noise and vibration levels according to standards.

REACH

Ordering Spare Parts

Maintenance and Repairs

Disposal

EC Declaration of Conformity

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