Stihl 025 Chainsaw Repair Manual

The Stihl 025 is a professional-grade chainsaw known for its reliability and power. This repair manual provides comprehensive instructions for maintenance, troubleshooting, and repair of the Stihl 025 chainsaw, covering the engine, fuel system, ignition, chain brake, bar, chain, and other critical components. Below are key sections for safety, specifications, maintenance procedures, troubleshooting, and parts diagrams.

Safety Precautions

Before performing any repair or maintenance, ensure the chainsaw is turned off, the spark plug wire is disconnected, and all safety gear is worn.

Safety Item	Description
Personal Protective Equipment (PPE)	Wear safety glasses, gloves, hearing protection, and chainsaw chaps.
Work Area	Work in a well-ventilated, clean, and dry area away from sparks or open flames.
Fuel Safety	Drain fuel before repairs. Use approved fuel containers.
Chain Tension	Ensure chain is properly tensioned and sharpened before operation.
Spark Plug	Disconnect spark plug wire to prevent accidental starting.
Chain Brake	Test chain brake functionality regularly.
Bar & Chain	Inspect for wear, cracks, or damage before each use.
Fasteners	Check all nuts, bolts, and screws for tightness.
Exhaust	Ensure muffler is securely attached and not blocked.
Cleanliness	Keep the chainsaw clean of sawdust, oil, and debris.

Specifications & Technical Data

Key technical specifications for the Stihl 025 chainsaw.

• Engine Type: 2-stroke, single-cylinder, air-cooled.
• Displacement: 45.4 cc (2.77 cu. in.).
• Power Output: 2.4 kW (3.2 hp).
• Fuel Tank Capacity: 0.55 L (18.6 fl. oz.).
• Oil Tank Capacity: 0.26 L (8.8 fl. oz.).
• Ignition System: Electronic, capacitor discharge.
• Spark Plug: Bosch WSR6F or equivalent, gap 0.5 mm (0.020 in.).
• Idle Speed: 2,800 rpm.
• Maximum Power Speed: 9,500 rpm.
• Guide Bar Lengths: 40 cm (16 in.) to 50 cm (20 in.).
• Chain Pitch: 3/8" or .325".
• Weight (without bar & chain): 5.2 kg (11.5 lbs).

Maintenance Schedule

Regular maintenance ensures optimal performance and longevity.

1. Before Each Use: Check chain tension, sharpness, and lubrication. Inspect for loose fasteners.
2. After Each Use: Clean air filter, check spark plug, clean cooling fins.
3. Weekly (or 5 hours): Clean fuel filter, inspect fuel lines, check chain brake.
4. Monthly (or 20 hours): Replace spark plug, clean carburetor, check ignition system.
5. Annually (or 100 hours): Replace fuel filter, inspect piston and cylinder, check clutch and sprocket.

WARNING! Always use genuine Stihl parts and lubricants. Improper maintenance can lead to failure or injury.

Engine Repair

Procedures for diagnosing and repairing engine components.

Cylinder & Piston: Inspect for scoring or wear. Replace if compression is below 110 psi. Use piston ring compressor for installation.

Crankshaft & Bearings: Check for play or roughness. Replace bearings if damaged.

Muffler: Clean carbon deposits regularly. Ensure spark arrestor screen is intact.

Cooling System: Keep cooling fins clean to prevent overheating.

Decompression Valve: Test for proper sealing. Replace if engine is hard to start.

Fuel System

Maintenance and repair of fuel system components.

1. Fuel Tank: Inspect for cracks. Clean with compressed air.
2. Fuel Filter: Replace if clogged. Located inside fuel tank.
3. Fuel Lines: Check for cracks or leaks. Replace if hardened or brittle.
4. Carburetor: Clean jets and diaphragm. Adjust H and L screws per specifications.
5. Fuel Cap: Ensure vent is not blocked.

Tip: Use fresh, high-quality 2-stroke oil mixed at 50:1 ratio with unleaded gasoline.

Ignition System

Diagnosis and repair of ignition components.

1. Spark Plug: Check gap (0.5 mm). Replace if electrode is worn or fouled.
2. Ignition Module: Test with multimeter. Replace if no spark is present.
3. Stop Switch: Ensure wire is intact and switch functions properly.
4. Flywheel & Key: Inspect for sheared key or damage to magnets.

WARNING! Always disconnect spark plug wire before testing ignition system.

Chain & Bar Assembly

Proper maintenance of cutting components.

1. Chain Sharpening: Use round file matching chain pitch. Maintain correct filing angle (30°).
2. Bar Maintenance: Clean bar groove. Flip bar regularly for even wear.
3. Chain Tension: Adjust so chain snaps back when pulled from bar.
4. Sprocket: Inspect for wear. Replace if teeth are hooked or damaged.
5. Oil Pump: Ensure oil flow to bar and chain. Adjust if necessary.

CAUTION! Always wear gloves when handling chain. A dull chain increases kickback risk.

Chain Brake System

Inspection and repair of the chain brake.

Band & Spring: Inspect for wear or fatigue. Replace if band is stretched or spring is weak.

Activation: Test by striking front hand guard. Chain should stop immediately.

Lever & Linkage: Ensure lever moves freely and linkage is not bent.

Cleaning: Keep brake mechanism free of sawdust and debris.

Troubleshooting Guide

Symptom	Possible Cause	Corrective Action
Engine won't start	No spark, flooded, fuel issue	Check spark plug, ignition; dry plug; clean carburetor.
Engine runs poorly	Clogged air filter, carb adjustment	Clean/replace air filter; adjust H/L screws.
Chain doesn't turn	Clutch worn, sprocket damaged	Inspect clutch shoes; replace sprocket.
Excessive vibration	Loose components, unbalanced bar	Tighten all fasteners; check bar for straightness.
Chain oil not flowing	Clogged oil passages, pump failure	Clean oil ports; check pump drive.
Overheating	Dirty cooling fins, lean fuel mix	Clean fins; adjust carburetor; check fuel mix.
Chain brake not engaging	Worn band, weak spring	Replace band and/or spring.

Reset: For electronic ignition, disconnect battery (if equipped) for 30 seconds.

Parts Diagrams & Ordering

Refer to official Stihl parts diagrams for part numbers and assembly order. Common replacement parts include:

• Piston & Cylinder Kit
• Carburetor Repair Kit
• Clutch Assembly
• Chain Brake Band
• Ignition Module
• Fuel Lines & Filter
• Guide Bar & Chain

Ordering: Use part numbers from diagrams. Contact authorized Stihl dealer or visit www.stihlusa.com.

Warranty & Service

Stihl 025 chainsaws are covered by a limited warranty. For service, contact an authorized Stihl servicing dealer.

Warranty Period: Varies by region; typically 1 year for consumer use.

Service Network: Locate dealers via www.stihl.com or call 1-800-467-8445.

Safety Recalls: Check Stihl website for any safety notices or recalls.

Copyright © 2025 Stihl. All trademarks are property of Andreas Stihl AG & Co. KG.