STIHL MS 170 Workshop Manual

The STIHL MS 170 is a lightweight, professional-grade chainsaw designed for occasional users and homeowners. This workshop manual provides detailed instructions for maintenance, troubleshooting, and repair. It covers safety procedures, technical specifications, engine components, fuel system, ignition system, cutting equipment, and step-by-step repair guides. Always refer to this manual and use proper tools before performing any service.

1. Safety Information 2. Technical Specifications 3. Component Overview 4. Maintenance Schedule 5. Engine Service 6. Fuel System 7. Ignition System 8. Cutting Equipment 9. Troubleshooting 10. Torque Specifications 11. Exploded Views & Parts List

Safety Information

Always wear appropriate personal protective equipment (PPE): safety glasses, hearing protection, gloves, chainsaw chaps, and sturdy boots. Work in a well-ventilated area. Ensure the chainsaw is stopped and cool before servicing. Disconnect the spark plug boot to prevent accidental starting. Use only STIHL-approved parts and lubricants.

Hazard	Precaution
Fuel Fires	Refuel in open area, away from ignition sources. Wipe spills immediately.
Hot Surfaces	Allow engine and muffler to cool before touching.
Sharp Components	Wear cut-resistant gloves when handling chain, guide bar, or sprocket.
Battery (if electric start)	Disconnect battery before electrical work.
Spring-Loaded Parts	Use caution when disassembling starter or clutch mechanisms.

Technical Specifications

Model: STIHL MS 170
Engine Type: Single-cylinder, two-stroke, air-cooled
Displacement: 30.1 cm³ (1.84 cu. in.)
Power Output: 1.3 kW (1.8 bhp)
Fuel Tank Capacity: 0.25 L (0.07 US gal)
Oil Tank Capacity: 0.145 L (0.04 US gal)
Recommended Fuel: Unleaded gasoline (min. 89 octane) mixed with STIHL HP Ultra oil at 50:1 ratio
Guide Bar Lengths: 30 cm (12"), 35 cm (14"), 40 cm (16")
Chain Pitch/Gauge: 3/8" PMM / 1.3 mm (0.050")
Weight (powerhead): 3.9 kg (8.6 lbs)
Ignition System: Electronic, capacitor discharge (CDI)
Spark Plug: NGK BPMR 7A (gap 0.5 mm / 0.020")

Component Overview

Key components: Engine cylinder, piston, carburetor, air filter, fuel filter, spark plug, ignition module, clutch, sprocket, guide bar, chain, chain brake, throttle trigger, throttle lockout, choke lever, master control lever, decompression valve (if equipped), muffler, anti-vibration system.

Engine: Cylinder, piston, crankshaft, connecting rod.
Fuel System: Fuel tank, cap, filter, lines, carburetor (WT-215).
Air System: Air filter cover, pre-filter, main filter element.
Ignition: Flywheel, ignition module, spark plug, stop switch.
Cutting Attachment: Guide bar, saw chain, drive sprocket, clutch drum, chain tensioner.
Safety: Chain brake, throttle lockout, right-hand guard.
Controls: Master control lever (choke/run/stop), throttle trigger.

WARNING! Never operate the chainsaw without the chain brake functioning correctly.

Maintenance Schedule

Regular maintenance ensures optimal performance and longevity. Follow this schedule based on usage hours or weekly/monthly intervals for occasional users.

Task	Before Each Use	Weekly / 5 Hours	Monthly / 20 Hours	Annually / 100 Hours
Check chain tension & sharpness	✓
Clean air filter		✓
Check fuel filter			✓
Clean spark arrestor screen			✓
Replace spark plug				✓
Clean cooling fins			✓
Inspect guide bar wear		✓
Lubricate drive sprocket			✓
Check all nuts & bolts	✓
Clean chain brake mechanism			✓

Engine Service

Includes cylinder/piston inspection, decompression valve service, and muffler maintenance.

Cylinder & Piston Inspection: Remove muffler to view piston through exhaust port. Look for scoring, scratches, or carbon buildup. Light scoring may be cleaned with fine emery cloth. Deep scoring requires cylinder/piston replacement.
Decompression Valve: If equipped, test by pressing valve button. It should spring back. Clean with carburetor cleaner if sticky. Replace if leaking compression.
Muffler: Remove and clean carbon deposits from spark arrestor screen. Ensure gasket is intact. Reinstall with proper torque.
Crankshaft Seals: Check for leaks by running engine at idle; spray soapy water around seals. Bubbles indicate leak requiring seal replacement.

CAUTION! Always use a piston stop tool when removing the flywheel or clutch to prevent crankshaft rotation.

Fuel System

Carburetor adjustment, fuel line replacement, and tank vent service.

Fuel Lines: Inspect for cracks or brittleness. Replace using STIHL part numbers. Route lines correctly to avoid kinks.
Fuel Filter: Replace if dirty or clogged. Ensure filter sits at bottom of tank.
Carburetor (WT-215): Standard adjustment: LA screw 1 turn open, H screw 1 turn open, L screw 1 turn open. Fine-tune for smooth acceleration and idle. For major service, rebuild with kit or replace unit.
Tank Vent: Located in fuel cap. Clean if fuel flow is restricted. Test by loosening cap briefly; if performance improves, replace vent.

Tip: Use only fresh fuel mix. Stale fuel is a common cause of starting and running issues.

Ignition System

Testing spark, replacing ignition module, and flywheel key.

Spark Test: Remove spark plug, reconnect boot, ground plug base against cylinder. Pull starter rope; look for strong blue spark. No spark indicates faulty plug, boot, wire, or ignition module.
Ignition Module (Coil): Check air gap between module legs and flywheel magnets (0.2-0.4 mm / 0.008-0.016"). Adjust by loosening screws. Replace module if no spark and gap is correct.
Flywheel Key: If engine timing is off or saw backfired, shear key may be broken. Remove flywheel and inspect keyway. Replace key with genuine part.
Stop Switch: Test continuity. Wire should be open circuit when switch is pressed (off).

WARNING! High voltage present. Do not touch spark plug electrode during test.

Cutting Equipment

Chain sharpening, guide bar maintenance, sprocket and clutch service.

Chain Sharpening: Use round file (4.0 mm / 5/32") and file guide. Maintain 30° top plate cutting angle and 10° down angle. File all cutters to equal length. Depth gauges must be filed to 0.65 mm (0.025") below cutter top plate.
Guide Bar: Clean bar groove with bar groove cleaner. Flip bar weekly for even wear. Dress rails with flat file if burred. Replace if groove is widened or rails are uneven.
Sprocket: Inspect drive sprocket (rim or spur type) for wear. Replace if teeth are hooked or worn unevenly.
Clutch: Remove clutch with special tool (STIHL 0000 893 4303). Inspect shoes for wear and springs for damage. Clean drum interior.
Chain Tensioner: Ensure mechanism moves freely. Replace if stripped or stuck.

CAUTION! Always wear gloves. A sharp chain is safer than a dull one as it requires less force.

Troubleshooting

Symptom	Possible Cause	Corrective Action
Engine will not start	No spark, stale fuel, flooded, clogged air filter	Check spark, use fresh fuel mix, clear flood (open throttle, pull starter), clean air filter.
Engine starts then dies	Fuel filter clogged, tank vent blocked, carburetor adjustment	Replace fuel filter, clean tank vent, adjust L screw.
Lacks power under load	Clogged spark arrestor, dirty air filter, carburetor H setting	Clean spark arrestor screen, clean air filter, adjust H screw.
Chain does not turn	Clutch worn, sprocket worn, chain brake engaged	Inspect clutch and sprocket, disengage chain brake.
Chain turns at idle	Idle speed too high, clutch springs weak	Adjust idle speed (L screw), replace clutch.
Excessive vibration	Unbalanced chain, loose components, AV mounts damaged	Sharpen chain evenly, tighten bolts, inspect anti-vibration mounts.
Oil not lubricating chain	Oil holes clogged, oil pump faulty, wrong oil viscosity	Clean bar and saw oil passages, test oil pump output, use STIHL chain oil.

Reset: For electronic issues (if applicable), disconnect battery/spark plug for 1 minute.

Torque Specifications

Use a calibrated torque wrench. Values in Nm (ft-lbs).

Component	Torque
Cylinder bolts (M6)	10 Nm (7.4 ft-lbs)
Muffler bolts	8 Nm (5.9 ft-lbs)
Clutch (left-hand thread)	40 Nm (29.5 ft-lbs)
Flywheel nut	35 Nm (25.8 ft-lbs)
Spark plug	20 Nm (14.8 ft-lbs)
Guide bar nuts	9 Nm (6.6 ft-lbs)
Handlebar bolts	12 Nm (8.9 ft-lbs)
Fuel tank bolts	6 Nm (4.4 ft-lbs)

Exploded Views & Parts List

Refer to official STIHL parts catalog for MS 170 (IPL) for complete diagrams and part numbers. Common replacement parts:

Piston Kit: 1120 030 2005
Cylinder: 1120 020 1201
Carburetor Kit: 1120 007 1065
Ignition Module: 1140 400 1301
Fuel Line: 1110 358 7700
Air Filter: 1120 120 1601
Clutch Assembly: 1120 160 2003
Drive Sprocket (Rim): 1120 007 1007
Chain Brake Band: 1120 650 0801

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