Stihl 025 Chainsaw Service Manual

The Stihl 025 is a professional-grade gasoline chainsaw designed for demanding cutting tasks. This manual provides comprehensive instructions for safe operation, routine maintenance, troubleshooting, and repair procedures. It covers engine specifications, fuel system, ignition, chain and bar assembly, lubrication, and safety features to ensure optimal performance and longevity of your chainsaw.

1. Safety Information & Warnings 2. Specifications & Technical Data 3. Component Identification 4. Assembly & Initial Setup 5. Fuel & Lubrication System 6. Engine Maintenance 7. Chain & Guide Bar Service 8. Ignition System 9. Troubleshooting Guide 10. Parts List & Diagrams 11. Warranty & Support

Safety Information & Warnings

Operating a chainsaw involves significant risk. Always read and understand all safety instructions before use.

Hazard	Precaution
Kickback	Always grip saw firmly with both hands. Use a low-kickback chain and maintain proper chain tension.
Hearing Damage	Wear approved hearing protection during operation.
Eye Injury	Always wear safety glasses or a face shield.
Fire/Explosion	Refuel in a well-ventilated area with engine off and cool. Avoid sparks or flames.
Vibration	Take regular breaks to reduce risk of Hand-Arm Vibration Syndrome (HAVS).

Specifications & Technical Data

Engine Type: Single cylinder, 2-stroke, air-cooled.
Displacement: 45.4 cc (2.77 cu. in.)
Power Output: 2.2 kW (3.0 hp)
Fuel Tank Capacity: 0.55 L (18.6 fl. oz.)
Oil Tank Capacity: 0.26 L (8.8 fl. oz.)
Guide Bar Lengths: 40 cm (16"), 45 cm (18") recommended.
Chain Pitch: 3/8" PMM or .325"
Ignition System: Electronic, capacitor discharge (CDI).
Weight (Powerhead): 5.2 kg (11.5 lbs) without bar and chain.

Component Identification

Key components: Front Hand Guard, Chain Brake, Throttle Trigger, Throttle Trigger Lockout, Master Control Lever, Decompression Valve, Muffler, Spark Plug, Fuel Tank Cap, Oil Tank Cap, Chain Tensioner, Guide Bar, Saw Chain.

Master Control Lever Positions: (I) Start/Idle, (0) Stop, (⏼) Warm Start/Full Throttle.

Assembly & Initial Setup

Assembling your new Stihl 025 chainsaw.

Attach Guide Bar & Chain: Place bar on studs. Loop chain over sprocket and onto bar groove, ensuring cutting teeth face forward on top. Install bar nut and adjust tension.
Fill Fuel Tank: Use fresh, high-quality gasoline mixed with Stihl HP Ultra 2-stroke oil at a 50:1 ratio.
Fill Chain Oil Tank: Use Stihl chain oil or a quality substitute.
Check Chain Tension: Chain should be snug against bar but pull freely by hand. Re-tension after initial warm-up.

WARNING! Never operate the saw without proper chain lubrication. Ensure all fasteners are tight.

Fuel & Lubrication System

Proper fuel mix and lubrication are critical for engine life.

Fuel Mix: Use 89 octane (or higher) unleaded gasoline. Mix with Stihl HP Ultra oil at a 50:1 ratio (2.6 fl. oz. oil per 1 gallon gas). Shake container thoroughly.

Chain Lubrication: The automatic oiler feeds oil to the guide bar. Check oil level before each use. Adjust oil flow rate via screw near oil tank if equipped.

Cleaning Fuel Filter: Periodically remove and clean the in-tank fuel filter. Replace if damaged.

Engine Maintenance

Routine maintenance ensures reliable operation.

Air Filter: Clean weekly under dusty conditions. Remove, tap clean, or wash in soapy water. Dry completely before reinstalling.
Spark Plug: Check gap (0.5 mm / 0.020"). Clean electrodes or replace if worn. Use Champion RCJ7Y or equivalent.
Cylinder Fins & Muffler: Keep cooling fins and muffler area free of sawdust and debris to prevent overheating.
Carburetor Adjustment: Factory preset. Only adjust LA (idle) and H (high speed) screws if necessary using a tachometer.

Chain & Guide Bar Service

Proper chain care is essential for cutting performance and safety.

Sharpening: Use a round file matching chain pitch (typically 4.0mm or 4.8mm). Maintain correct filing angle (usually 30°). File all cutters to equal length.
Depth Gauge Setting: Regularly check and file down depth gauges (rakers) using a depth gauge tool to prevent kickback.
Bar Maintenance: Clean bar groove weekly. Flip bar monthly for even wear. Dress bar rails with a flat file if burred.
Sprocket: Inspect drive sprocket for wear. Replace if teeth are hooked or worn thin.

Ignition System

The electronic ignition requires minimal service.

Spark Plug Wire: Inspect for cracks or damage.
Stop Switch: Test for continuity. The switch must ground the ignition to stop the engine.
Ignition Module (CDI): If engine has no spark, check all connections first. Module replacement requires specific testing procedures.

CAUTION! Disconnect the spark plug boot before performing any maintenance to prevent accidental starting.

Troubleshooting Guide

Symptom	Possible Cause	Corrective Action
Engine will not start	No fuel, flooded, bad spark, switch off	Check fuel, dry plug, check spark, ensure switch is on (I).
Engine starts then dies	Clogged fuel filter, carburetor issues, vent blocked	Clean/replace fuel filter, check carburetor settings, clear tank vent.
Loss of power	Clogged air filter, muffler screen blocked, improper fuel mix	Clean air filter, clean spark arrestor screen, use fresh 50:1 mix.
Chain does not oil	Empty oil tank, clogged oil passage, faulty oil pump	Fill tank, clean bar oil holes and tank outlet, inspect pump.
Excessive vibration	Loose components, unbalanced chain, damaged AV mounts	Tighten all fasteners, sharpen chain evenly, inspect anti-vibration buffers.

Parts List & Diagrams

Refer to the official Stihl 025 IPL (Illustrated Parts List) for part numbers and exploded-view diagrams of the cylinder/piston group, carburetor assembly, clutch and oil pump, ignition system, and housing components. Always use genuine Stihl replacement parts.

Warranty & Support

Stihl offers a limited warranty for the 025 chainsaw. Proof of purchase from an authorized Stihl dealer is required. Warranty does not cover damage from misuse, improper fuel, or lack of maintenance.

For Service: Contact your local authorized Stihl servicing dealer. Do not attempt repairs beyond your skill level.

Support: www.stihlusa.com or call 1-800-467-8445.