STIHL MS 170 Service Manual PDF

The STIHL MS 170 is a lightweight, easy-to-handle chainsaw designed for occasional users and homeowners. This service manual provides comprehensive information for maintenance, troubleshooting, and repair of the MS 170 model. It covers safety precautions, technical specifications, engine and cutting system maintenance, fuel system servicing, ignition system checks, and detailed disassembly/assembly procedures. Below are key sections for safe operation, maintenance schedules, component specifications, and step-by-step repair guides.

Safety Information & Warnings

Essential safety rules for operating and servicing the STIHL MS 170 chainsaw.

Hazard	Precaution
Kickback	Always hold saw firmly with both hands; use reduced-kickback chain and bar.
Fuel Handling	Use approved fuel containers; refuel in well-ventilated area away from ignition sources.
Hot Surfaces	Allow engine and muffler to cool before performing maintenance.
Chain Tension	Check and adjust chain tension regularly; a loose chain can derail.
Personal Protective Equipment (PPE)	Always wear safety glasses, hearing protection, gloves, and chainsaw chaps or pants.
Working Area	Ensure clear work area; be aware of bystanders and obstacles.
Sharpening	Secure saw and use proper filing tools; wear cut-resistant gloves.
Electrical Shock	Disconnect spark plug wire before performing any service on engine or ignition system.

Technical Specifications

• Engine Type: STIHL single-cylinder two-stroke engine.
• Displacement: 30.1 cc (1.84 cu. in.).
• Power Output: 1.5 kW (2.0 bhp).
• Fuel Tank Capacity: 0.25 liters (0.066 US gal).
• Oil Tank Capacity: 0.145 liters (0.038 US gal).
• Guide Bar Lengths: Typically 12", 14", or 16" (30 cm, 35 cm, or 40 cm).
• Chain Pitch: 3/8" PMM3 (Picco Micro Mini 3).
• Chain Gauge: 0.043" (1.1 mm).
• Ignition System: Electronic, capacitor discharge ignition (CDI).
• Weight (powerhead only): Approximately 3.9 kg (8.6 lbs).

Maintenance Schedule

Regular maintenance ensures optimal performance and longevity.

1. Before Each Use: Check chain tension, sharpness, and lubrication. Inspect for loose fasteners and damage.
2. After Each Use: Clean air intake, cooling fins, and guide bar. Wipe down entire saw.
3. Every 5 Hours of Operation: Clean or replace air filter. Check spark plug condition.
4. Every 10 Hours: Clean spark arrestor screen in muffler (if equipped).
5. Every 20 Hours: Replace fuel filter. Check fuel lines for cracks.
6. Every Season or 50 Hours: Replace spark plug. Clean carburetor and check adjustment. Inspect anti-vibration elements.
7. As Needed: Sharpen chain, replace guide bar, replace drive sprocket.

WARNING! Always follow safety procedures. Use only genuine STIHL parts for replacement.

Engine System

Procedures for maintaining and servicing the two-stroke engine.

Cylinder & Piston: Inspect for scoring, carbon buildup, and ring wear. Measure compression (minimum 110 psi).

Air Filter: Remove, clean with compressed air or wash in soapy water (if foam type). Allow to dry completely before reinstalling.

Muffler/Spark Arrestor: Remove and clean carbon deposits from exhaust port and spark arrestor screen.

Cooling System: Ensure cooling fins on cylinder are clean and free of debris.

Fuel System

Servicing the carburetor, fuel lines, and tank.

1. Disconnect spark plug wire.
2. Drain fuel tank completely.
3. Remove carburetor cover and air filter.
4. Inspect fuel lines for brittleness or cracks; replace if necessary.
5. Clean carburetor exterior. For internal cleaning, disassemble using appropriate tools, clean jets and diaphragms with carburetor cleaner.
6. Replace fuel filter inside the tank.
7. Reassemble, ensuring all gaskets and diaphragms are correctly positioned.
8. Adjust carburetor (LA, H screws) according to STIHL specifications using a tachometer.

Tip: Use fresh, high-quality fuel mix (50:1 gasoline to STIHL HP Ultra oil).

Ignition System

Testing and replacing ignition components.

Spark Plug: Type: Bosch WSR 6F or equivalent. Gap: 0.020" (0.5 mm). Check for fouling, cracked porcelain, or eroded electrode.

Ignition Module (CDI): Test with multimeter for proper resistance or spark output. Ensure air gap between flywheel and module is correct (0.3 mm / 0.012").

Stop Switch: Test for continuity. Ensure wire is not pinched or damaged.

Wiring: Inspect all wires for breaks or poor connections.

Cutting Attachment

Maintenance of guide bar, chain, and sprocket.

1. Guide Bar: Clean bar groove regularly. Flip bar weekly for even wear. Check for straightness and worn rails.
2. Chain: Sharpen regularly with correct round file size (typically 4.0 mm / 5/32"). Maintain correct filing angle (typically 30°). Ensure depth gauges (rakers) are properly filed down.
3. Drive Sprocket: Inspect for wear (pointed teeth). Replace if worn, preferably with a matching rim sprocket system.
4. Chain Brake: Test functionality. Inspect band and mechanism for damage or wear.
5. Chain Catcher: Ensure it is intact and securely mounted.

WARNING! A dull or improperly tensioned chain increases kickback risk and reduces cutting efficiency.

Troubleshooting Guide

Symptom	Possible Cause	Corrective Action
Engine will not start	No spark, flooded, fuel issues	Check spark plug, ignition. Wait if flooded. Check fuel lines, filter, carburetor.
Engine starts then dies	Clogged fuel filter, carb adjustment, air leak	Replace fuel filter. Adjust carburetor. Check crankcase seals and intake boot.
Loss of power	Clogged air filter, muffler, carb issues	Clean/replace air filter. Clean muffler/spark arrestor. Service carburetor.
Chain does not turn	Clutch worn, sprocket, brake engaged	Inspect clutch shoes and springs. Check drive sprocket. Disengage chain brake.
Excessive vibration	Loose components, unbalanced chain, AV mounts	Tighten all fasteners. Balance chain. Inspect and replace anti-vibration mounts.
Chain throws oil	Oil port clogged, pump adjustment	Clean oil passages in bar and saw. Check and adjust oil pump output.

Disassembly & Assembly

Key procedures for major component removal.

Removing the Engine Covers: Remove starter cover screws, then the fuel tank/rear handle assembly screws. Carefully separate halves, noting routing of control wires and fuel lines.

Removing the Cylinder: Remove muffler, intake manifold, and cylinder base nuts. Gently tap cylinder to break gasket seal. Lift cylinder off crankcase.

Removing the Clutch: Use a clutch holding tool to prevent crankshaft rotation. Unscrew clutch nut (left-hand thread). Remove clutch drum and needle bearing.

Reassembly Notes: Use new gaskets and seals. Apply thread locker to specified fasteners. Torque all fasteners to specification.

Torque Specifications

• Cylinder Base Nuts: 10 Nm (88 in-lb)
• Spark Plug: 20 Nm (15 ft-lb)
• Clutch Nut: 40 Nm (30 ft-lb) - LEFT-HAND THREAD
• Flywheel Nut: 40 Nm (30 ft-lb)
• Guide Bar Nuts: 9-10 Nm (80-88 in-lb)
• Muffler Screws: 8 Nm (71 in-lb)
• Handle Mounting Screws: 8 Nm (71 in-lb)

CAUTION! Overtightening can strip threads or damage components. Use a calibrated torque wrench.

Parts List & Diagrams

Reference for ordering genuine STIHL replacement parts. Diagrams include exploded views of:

1. Complete Powerhead Assembly
2. Engine Group (Crankcase, Piston, Cylinder)
3. Fuel System (Tank, Lines, Carburetor)
4. Ignition System (Flywheel, Module, Wiring)
5. Clutch & Drive Sprocket Assembly
6. Cutting Attachment (Guide Bar, Chain, Sprocket)
7. Starter Assembly
8. Anti-Vibration System
9. External Covers and Handles

Part numbers are subject to change. Always verify with your STIHL dealer using the saw's serial number.

Service Support: For technical assistance or to order parts, contact an authorized STIHL servicing dealer or visit www.stihlusa.com.