Stihl MS 270 Service Manual

The Stihl MS 270 is a professional-grade chainsaw featuring a powerful engine, anti-vibration system, quick-stop chain brake, and easy-to-service components. This manual provides comprehensive instructions for maintenance, troubleshooting, repair, and safety procedures. Below are key sections covering specifications, safety, maintenance schedules, component service, and troubleshooting.

Features at a Glance

Key components: Engine, fuel system, ignition system, chain brake, anti-vibration handles, chain tensioner, air filter, and exhaust system.

Safety Information

Always wear appropriate PPE: safety glasses, hearing protection, gloves, chainsaw chaps, and steel-toed boots.

1. Work in a well-ventilated area away from sparks or open flames.
2. Disconnect spark plug wire before performing any service.
3. Use only STIHL-approved replacement parts and lubricants.
4. Ensure chainsaw is cool before servicing.
5. Follow local regulations for disposal of fuel, oil, and filters.

WARNING! Fuel is highly flammable. Do not smoke or work near ignition sources. Chain must be properly tensioned and sharpened to prevent kickback.

Maintenance Schedule

Regular maintenance ensures optimal performance and longevity.

1. Daily/Before Use: Check chain tension, sharpness, and lubrication; inspect for loose fasteners; clean air filter.
2. Every 10 Hours: Clean spark arrestor screen; check fuel filter.
3. Every 20 Hours: Replace air filter; inspect spark plug; clean cooling fins.
4. Every 50 Hours: Clean carburetor; replace fuel filter; check anti-vibration elements.
5. Every 100 Hours: Decarbonize exhaust port and muffler; inspect piston and cylinder through exhaust port.
6. Annually: Replace spark plug; inspect fuel lines and impulse line.

CAUTION! Always use genuine STIHL parts. Improper maintenance can void warranty and cause unsafe operation.

Specifications

• Engine: 2-stroke, 50.2 cc, bore 45.0 mm, stroke 31.6 mm.
• Powerhead Weight: 5.2 kg (11.5 lbs).
• Fuel/Oil Ratio: 50:1 (STIHL HP Ultra or equivalent ISO-L-EGD certified oil).
• Idle Speed: 2,800 RPM.
• Maximum Power Speed: 9,500 RPM.
• Ignition Air Gap: 0.3 mm (0.012 in).
• Spark Plug: Bosch WSR6F or equivalent, gap 0.5 mm (0.020 in).
• Chain Oil: STIHL HP Ultra or biodegradable chain oil.
• Sound Pressure Level: 106 dB(A).
• Vibration Level: Front handle 4.2 m/s², rear handle 2.8 m/s².

Component Identification

Major components: Cylinder, piston, crankshaft, carburetor, fuel tank, oil tank, chain brake, clutch, sprocket, guide bar, chain, air filter, muffler, spark plug, ignition module, anti-vibration springs.

Controls: Master Control Lever (combines choke, throttle lock, stop switch), throttle trigger, throttle lockout, chain brake lever, decompression valve (if equipped).

Fasteners: Use appropriate torque values: cylinder bolts 10 Nm, clutch 35 Nm, guide bar nuts 9-10 Nm.

Fuel System Service

Includes fuel tank, filter, lines, and carburetor.

1. Drain fuel tank before service.
2. Replace fuel filter: Disconnect fuel line, insert new filter, reconnect.
3. Inspect fuel lines for cracks or hardening; replace if necessary.
4. Clean fuel tank vent.
5. Carburetor service: Remove, disassemble, clean jets and diaphragms, reassemble with new gaskets if needed.

Tip: Use compressed air to blow out passages. Never use wire to clean jets.

Ignition System Service

Components: Spark plug, ignition module, flywheel, stop switch, wiring.

1. Check spark plug: Clean or replace if electrode is worn or fouled. Set gap to 0.5 mm.
2. Test ignition module with multimeter: Primary resistance approx. 1.0-1.2 Ω, secondary 12-14 kΩ.
3. Inspect flywheel key for shear; ensure tight mounting.
4. Check stop switch continuity; replace if faulty.
5. Set ignition air gap: 0.3 mm between flywheel magnets and ignition module poles.

WARNING! Always disconnect spark plug wire during testing to prevent accidental starting.

Chain & Bar Maintenance

Proper chain care is critical for safety and performance.

1. Sharpening: Use correct round file size (typically 4.0 mm or 5/32"). Maintain 30° cutting angle, 10° top plate angle.
2. Tensioning: Loosen bar nuts, adjust tensioning screw until chain snaps back when pulled from bar.
3. Bar maintenance: Clean bar groove, flip bar regularly for even wear, file down burrs on rails.
4. Lubrication: Ensure oiler is working; adjust flow if adjustable. Use proper chain oil.
5. Sprocket inspection: Replace if worn (teardrop shape).

CAUTION! A dull or loose chain increases kickback risk. Always stop engine before adjusting chain.

Carburetor Adjustment

Adjust at operating temperature with sharp chain.

1. Initial settings: Turn H and L needles gently clockwise to seat, then open H 1 turn, L 1 turn.
2. Start engine, warm up for several minutes.
3. Adjust idle speed (LA screw): Set to 2,800 RPM or so chain just stops moving.
4. Adjust L (low speed): Turn for fastest idle, then rich slightly (1/8 turn counterclockwise).
5. Adjust H (high speed): With throttle fully open, turn for max RPM, then lean slightly (1/8 turn clockwise) to achieve 12,800-13,200 RPM under load (use tachometer).
6. Recheck idle and acceleration.

Note: H needle limited by EPA restrictions; may not be adjustable on some models.

Disassembly & Assembly

General procedure for engine disassembly.

1. Remove top cover, air filter, carburetor, and fuel tank.
2. Remove muffler and cylinder cover.
3. Remove clutch using clutch tool; remove flywheel with puller.
4. Remove cylinder bolts; lift cylinder carefully.
5. Remove piston pin circlips; push out pin; remove piston.
6. Inspect crankshaft bearings and seals.
7. Assembly in reverse order. Use new gaskets and seals. Lubricate piston and cylinder with 2-stroke oil.
8. Torque cylinder bolts in crisscross pattern to 10 Nm.

WARNING! Label parts and fasteners. Do not force components. Check service manual for specific torque values.

Troubleshooting

Reset: For electronic ignition issues, check module grounding and wiring.

Service: For technical support or parts, contact authorized STIHL servicing dealer or visit www.stihlusa.com.