STIHL MS 311 Repair Manual

The STIHL MS 311 is a professional-grade chainsaw featuring a 59.0 cc engine, STIHL Quickstop® inertia chain brake, Ematic™ lubrication system, and anti-vibration system. This repair manual provides detailed instructions for troubleshooting, maintenance, disassembly, and reassembly of key components including the engine, fuel system, ignition, chain brake, and cutting attachments. Below are key sections for safety, specifications, troubleshooting, maintenance procedures, and parts identification.

Features at a Glance

Key components: Engine, carburetor, ignition module, chain brake, clutch, oil pump, anti-vibration system.

Feature	Description
Engine Displacement	59.0 cc, 2-stroke
Power Output	3.4 kW (4.6 bhp)
Fuel Tank Capacity	550 ml
Oil Tank Capacity	260 ml
Guide Bar Lengths	40 cm (16"), 45 cm (18"), 50 cm (20")
Chain Pitch	3/8"
Ignition System	Electronic, capacitor discharge
Carburetor	STIHL Zama C1Q-S167
Weight (powerhead)	6.2 kg
Anti-Vibration	STIHL AV system

Safety Precautions

Always wear protective equipment. Disconnect spark plug before servicing.

1. Work in well-ventilated area away from ignition sources.
2. Use STIHL-approved tools and replacement parts.
3. Secure saw in vise during disassembly.
4. Clean parts thoroughly before inspection.

WARNING! Fuel is highly flammable. Allow engine to cool before servicing. Always wear safety glasses and gloves.

Specifications

• Engine Type: Single cylinder, 2-stroke, air-cooled.
• Bore x Stroke: 47.0 mm x 34.0 mm.
• Compression Ratio: 7.5:1.
• Fuel Mix: 50:1 (STIHL HP Ultra oil with unleaded gasoline).
• Idle Speed: 2,800 RPM.
• Maximum Power Speed: 9,500 RPM.
• Spark Plug: NGK BPMR 7A, gap 0.5 mm.
• Chain Oil: STIHL HP Ultra chain oil or equivalent.
• Warranty: 12 months commercial use, 24 months private use.

Troubleshooting Guide

Common problems and solutions for STIHL MS 311.

Symptom	Possible Cause	Corrective Action
Engine won't start	Fuel stale, spark plug fouled	Drain fuel, replace with fresh mix; clean/replace spark plug.
Engine runs poorly	Clogged air filter, carb adjustment	Clean air filter; adjust carburetor H/L screws per manual.
Chain won't turn	Clutch worn, sprocket damaged	Inspect clutch shoes and drum; replace if worn.
Excessive vibration	AV mounts damaged, loose parts	Check anti-vibration buffers; tighten all fasteners.
Oil not lubricating	Oil pump faulty, lines clogged	Test oil pump output; clean oil passages and filter.

Note: Always refer to torque specifications when reassembling.

Maintenance Schedule

Regular maintenance ensures optimal performance and longevity.

1. Daily: Check chain tension, sharpness, and lubrication.
2. Weekly: Clean air filter, check spark plug, inspect bar and chain wear.
3. Monthly: Clean cooling fins, check fuel filter, inspect clutch and sprocket.
4. Annually: Replace fuel lines, clean carburetor, check cylinder compression.

CAUTION! Use only STIHL-approved parts. Incorrect maintenance can void warranty.

Fuel System Repair

Carburetor adjustment and fuel line replacement procedures.

1. Remove carburetor cover and air filter.
2. Identify adjustment screws: L (low speed), H (high speed), LA (idle).
3. Initial settings: L = 1 turn open, H = 1 turn open.
4. Adjust at operating temperature for smooth acceleration.
5. Replace fuel lines if cracked or hardened.
6. Clean fuel tank and replace filter.

WARNING! Never run engine lean (insufficient fuel). This can cause engine seizure.

Ignition System Service

Testing and replacing ignition module and spark plug.

1. Disconnect spark plug wire and remove plug.
2. Check electrode gap (0.5 mm) and condition.
3. Test for spark: Ground plug against cylinder, pull starter.
4. If no spark, check stop switch wiring and ignition module resistance.
5. Replace module if primary resistance is outside 0.8–1.2 Ω.

Tip: Keep ignition components clean and dry.

Chain Brake & Clutch

Disassembly and inspection of safety and drive components.

1. Remove side cover, clutch cover, and bar.
2. Inspect brake band for wear or cracks.
3. Check clutch shoes for wear; replace if worn beyond service limit.
4. Lubricate clutch bearing with high-temperature grease.
5. Test brake function: Hand guard should engage brake smoothly.

WARNING! Never operate saw with faulty chain brake. Replace worn parts immediately.

Cylinder & Piston

Compression testing and cylinder/piston inspection.

1. Perform compression test: Minimum 110 psi for proper operation.
2. Remove muffler to inspect piston through exhaust port.
3. Look for scoring, aluminum transfer, or ring damage.
4. If scoring is present, disassemble engine for further inspection.
5. Measure cylinder bore and piston skirt wear with micrometer.

CAUTION! Always replace piston rings when reassembling. Use new gaskets.

Parts Diagrams

Reference diagrams for ordering correct replacement parts.

• Group 1: Cylinder, piston, crankshaft.
• Group 2: Carburetor, fuel tank, lines.
• Group 3: Ignition system, flywheel, starter.
• Group 4: Chain brake, clutch, sprocket.
• Group 5: Guide bar, chain, oil pump.
• Group 6: Housing, anti-vibration elements.

Note: Always use STIHL part numbers when ordering.

Torque Specifications

Component	Torque (Nm)	Thread Size
Cylinder bolts	10 Nm	M6
Clutch nut	40 Nm	M14 x 1.25
Flywheel nut	35 Nm	M12 x 1.25
Spark plug	25 Nm	M14 x 1.25
Guide bar nuts	9 Nm	M8
Muffler bolts	8 Nm	M6

Reset: After major repairs, reset maintenance interval indicator if equipped.

Service: For technical support, contact STIHL authorized service center or visit www.stihlusa.com.