Stihl Chainsaw MS170 Service Repair Manual

The Stihl MS170 is a lightweight, easy-to-use chainsaw designed for homeowners and occasional users. This service and repair manual provides detailed instructions for maintenance, troubleshooting, and repair procedures to ensure optimal performance and safety. Below are key sections covering safety, specifications, maintenance schedules, disassembly, repair, and troubleshooting.

Safety Information

Always prioritize safety when servicing the Stihl MS170 chainsaw. Wear appropriate personal protective equipment (PPE).

Specifications

• Model: Stihl MS170
• Engine Type: 2-stroke, single cylinder, air-cooled
• Displacement: 30.1 cc (1.84 cu. in.)
• Power Output: 1.5 kW (2.0 bhp)
• Fuel Tank Capacity: 0.25 L (0.07 US gal)
• Oil Tank Capacity: 0.145 L (0.04 US gal)
• Chain Pitch: 3/8" PMM3
• Bar Length Options: 12", 14", 16"
• Ignition System: Electronic, capacitor discharge (CDI)
• Spark Plug: Bosch WSR6F or equivalent, gap 0.5 mm (0.020 in)
• Idle Speed: 2,800 RPM
• Max Engine Speed: 13,000 RPM
• Weight (powerhead only): 3.9 kg (8.6 lbs)

Maintenance Schedule

Regular maintenance ensures longevity and safe operation.

1. Before Each Use: Check chain tension, sharpness, and lubrication. Inspect for loose fasteners and damage.
2. Every 10 Hours: Clean air filter. Check spark plug condition and gap.
3. Every 20 Hours: Clean cooling fins and exhaust ports. Check fuel filter.
4. Every 50 Hours: Replace spark plug. Clean or replace fuel filter. Check carburetor adjustment.
5. Every 100 Hours: Replace air filter. Clean carburetor. Check clutch and sprocket.
6. Annually: Replace fuel lines if cracked. Clean fuel tank. Inspect anti-vibration elements.

WARNING! Always use genuine Stihl parts and specified lubricants.

Engine System

Cylinder, piston, crankshaft, and connecting rod service procedures.

1. Cylinder Inspection: Check for scoring, wear, or damage. Measure bore diameter.
2. Piston & Rings: Inspect for carbon buildup, ring wear, and pin fit. Replace if out of spec.
3. Crankshaft & Bearings: Check for play, runout, and bearing smoothness.
4. Compression Test: Should be 120-150 psi. Low compression indicates worn rings, cylinder, or leaking seals.
5. Decompression Valve: Test for proper sealing and operation.

Torque Specifications: Cylinder bolts: 10 Nm (7.4 ft-lb). Spark plug: 25 Nm (18.4 ft-lb).

Fuel System

Carburetor, fuel lines, tank, and filter service.

1. Carburetor Adjustment: Standard settings: L (low speed) - 1 turn out; H (high speed) - 1 turn out. Fine-tune for smooth acceleration.
2. Fuel Filter Replacement: Drain tank. Remove filter through filler neck using hook tool.
3. Fuel Lines: Inspect for cracks, stiffness, or leaks. Replace if damaged.
4. Fuel Tank Vent: Ensure vent is clear. Test by loosening cap; if performance improves, replace vent.
5. Fuel Mix: Use 50:1 mix of unleaded gasoline (min 89 octane) and Stihl HP Ultra or equivalent 2-stroke oil.

CAUTION! Do not run engine without proper fuel/oil mix to avoid engine seizure.

Ignition System

Spark plug, ignition module (CDI), and flywheel service.

1. Spark Plug: Clean electrodes, check gap (0.5 mm / 0.020 in). Replace if electrodes are worn or insulator cracked.
2. Ignition Module (CDI): Test with multimeter per resistance specs. Replace if no spark.
3. Flywheel: Check for cracks, damaged keyway, or magnets. Torque nut to 40 Nm (29.5 ft-lb).
4. Stop Switch: Test continuity. Should be open when off, closed when on.
5. Spark Arrestor: Clean screen in muffler every 20 hours to prevent overheating.

Tip: Use a spark tester to verify strong, blue spark.

Chain & Bar

Chain tensioning, sharpening, bar maintenance, and sprocket service.

1. Chain Tension: Adjust so chain snaps back when pulled from bar. Tighten bar nuts after adjustment.
2. Sharpening: Use correct round file size (4.0 mm). Maintain 30° cutting angle, 10° top plate angle.
3. Bar Maintenance: Clean bar groove, flip bar regularly for even wear. Dress rails with flat file if burred.
4. Drive Sprocket: Inspect for wear. Replace if teeth are hooked or worn more than 0.5 mm.
5. Chain Lubrication: Ensure oiler port is clear. Use Stihl chain oil or equivalent. Adjust oil flow as needed.

WARNING! Always wear gloves when handling chain. A sharp chain is safer and more efficient.

Cooling & Exhaust

Air cooling system and muffler service.

1. Cooling Fins: Clean fins on cylinder and flywheel. Blocked fins cause overheating.
2. Muffler: Remove carbon deposits. Check for cracks or loose bolts.
3. Spark Arrestor Screen: Remove, clean with wire brush, or replace if damaged.
4. Air Flow: Ensure no debris blocks intake area around starter housing.

CAUTION! Muffler gets extremely hot. Allow engine to cool completely before servicing.

Disassembly & Assembly

Step-by-step guide for major component removal and installation.

1. Remove Top Cover: Remove two nuts. Disconnect choke linkage if necessary.
2. Remove Fuel Tank: Drain fuel. Remove screws securing tank to crankcase.
3. Remove Cylinder: Remove muffler, decomp valve, and cylinder bolts. Lift cylinder off.
4. Remove Crankshaft: Requires splitting crankcase. Mark halves for alignment.
5. Reassembly: Use new gaskets and seals. Apply thread locker to critical fasteners. Torque to specifications.

Tip: Take photos during disassembly to aid reassembly.

Troubleshooting

Reset: For electronic issues, disconnect spark plug wire for 30 seconds to reset module.

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

Parts List

Common replacement parts for Stihl MS170 (partial list). Always verify part numbers with your serial number.

Note: Parts may vary by production year. Always reference the specific IPL (Illustrated Parts List) for your serial number.