STIHL MS170 Workshop Manual

The STIHL MS170 is a lightweight, compact chainsaw designed for occasional users and homeowners. This workshop manual provides detailed technical information, maintenance procedures, troubleshooting guides, and repair instructions for the MS170 model. Below are key sections covering safety, specifications, maintenance, disassembly, troubleshooting, and reassembly.

1. Features at a Glance 2. Safety Precautions 3. Technical Specifications 4. Maintenance Schedule 5. Engine System 6. Fuel System 7. Ignition System 8. Chain & Bar Assembly 9. Disassembly Procedure 10. Troubleshooting 11. Reassembly & Torque Specifications

Features at a Glance

Key components: STIHL 2-MIX engine, side-access chain tensioner, Ematic lubrication system, Quickstop chain brake, and lightweight design.

Feature	Description
Engine Type	STIHL 2-MIX single-cylinder, air-cooled, 2-stroke
Displacement	30.1 cc
Power Output	1.5 kW (2.0 bhp)
Fuel Tank Capacity	250 ml
Oil Tank Capacity	145 ml
Guide Bar Lengths	12", 14", 16" (30, 35, 40 cm)
Chain Pitch	1/4" PMM3
Weight (powerhead)	3.9 kg (8.6 lbs)
Ignition System	Electronic, capacitor discharge (CDI)
Starter	STIHL ErgoStart (optional)

Safety Precautions

Always prioritize safety when performing maintenance or repairs.

Work in a clean, well-ventilated area away from ignition sources.
Disconnect the spark plug boot before any service to prevent accidental starting.
Use proper STIHL tools or equivalents as specified.
Wear appropriate personal protective equipment (PPE): safety glasses, gloves.
Handle fuel and oil with care; clean spills immediately.

WARNING! Failure to follow safety procedures can result in serious injury or death. The chainsaw must be completely cool before beginning work.

Technical Specifications

Model: STIHL MS170
Engine: 30.1 cc STIHL 2-MIX engine
Idle Speed: 2,800 rpm
Maximum Power Speed: 12,000 rpm
Carburetor: Zama C1Q-S137 (fixed-jet)
Spark Plug: Bosch WSR6F or equivalent, gap 0.5 mm (0.020")
Fuel Mix: 50:1 (Unleaded gasoline 89 octane min. to STIHL HP Ultra oil)
Chain Oil: STIHL HP or equivalent biodegradable chain oil
Sound Pressure Level: 103 dB(A)
Vibration Level: 4.5 m/s² (front/handle)

Maintenance Schedule

Access OSD via TV MENU or SETUP (DVD). Front Panel: POWER, OPEN/CLOSE, AUTO/DPMS, MUTE.

Daily/Before Use: Check chain tension, sharpness, and lubrication. Inspect for loose fasteners. Check throttle trigger and lockout function.
Weekly/Every 10 Hours: Clean air filter. Check spark plug condition and gap. Clean external surfaces and cooling fins.
Monthly/Every 20 Hours: Clean spark arrestor screen (if equipped). Check fuel filter and line. Inspect chain brake function.
Annually/Every 50 Hours: Replace fuel filter. Clean carburetor and fuel tank. Check all rubber mounts and antivibration elements.

Engine System

Cylinder & Piston: Inspect for scoring, carbon buildup, and ring wear. Crankshaft & Bearings: Check for play and smooth rotation. Muffler: Clean carbon deposits from exhaust port and spark arrestor.

Remove muffler cover and spark arrestor screen for cleaning.
Inspect cylinder through exhaust port using a borescope if available.
Measure compression: Should be above 120 psi (8.3 bar) for proper operation.

Tip: Always use a piston stop when removing the clutch or flywheel.

Fuel System

Carburetor (Zama C1Q-S137): Fixed high and low-speed jets. Fuel Tank & Lines: Check for cracks and deterioration.

Drain fuel tank completely before disassembly.
Remove carburetor cover, air filter, and intake boot.
Disconnect fuel lines and throttle linkage.
Clean carburetor with compressed air; do not use wire to clean jets.
Inspect fuel filter and replace if clogged.
Reassemble, ensuring all gaskets and diaphragms are correctly positioned.

WARNING! Fuel is highly flammable. No smoking or open flames in the work area.

Ignition System

Ignition Module (CDI): Non-adjustable, checks for spark output. Spark Plug: Standard Bosch WSR6F. Stop Switch: Tests for continuity.

Chain & Bar Assembly

Guide Bar: Inspect for wear, straightness, and groove damage. Chain: Check for sharpness, damaged cutters, and correct tension. Sprocket: Inspect drive sprocket (rim type) for wear.

CAUTION! Always wear cut-resistant gloves when handling the chain.

Disassembly Procedure

General sequence: Remove external covers, handle, chain brake assembly, clutch, flywheel, cylinder, and crankshaft.

Remove top and rear handle covers.
Remove chain brake band and clutch cover.
Use clutch tool to remove clutch (left-hand thread).
Use flywheel puller to remove flywheel.
Remove cylinder base nuts and carefully lift cylinder.
Support crankshaft when removing from crankcase.

Note: Label or photograph components and fasteners during disassembly for correct reassembly.

Troubleshooting

Symptom	Possible Cause	Corrective Action
Engine will not start	No spark, flooded, fuel issue	Check spark plug and ignition. Check fuel line, filter, and carburetor. Ensure choke is off for starting.
Engine starts then dies	Clogged fuel filter, carburetor adjustment	Replace fuel filter. Clean carburetor. Check tank vent.
Loss of power	Clogged air filter, exhaust port, poor compression	Clean air filter and muffler. Check cylinder and piston for wear.
Chain does not turn	Clutch worn, sprocket damaged, chain brake engaged	Inspect clutch shoes and springs. Check drive sprocket. Disengage chain brake.
Excessive vibration	Loose components, unbalanced chain, engine mount damage	Tighten all fasteners. Balance chain. Inspect antivibration mounts.
Chain oil not flowing	Clogged oil passages, worn oil pump, incorrect oil	Clean oil ports and filter. Inspect oil pump drive and worm gear. Use correct oil viscosity.

Reset: N/A for this model.

Service: For genuine STIHL parts and technical support, contact an authorized STIHL servicing dealer.

Reassembly & Torque Specifications

Cylinder Base Nuts: 10 Nm (88 in-lb)
Muffler Bolts: 8 Nm (71 in-lb)
Clutch: 35 Nm (310 in-lb) - LEFT-HAND THREAD
Flywheel Nut: 40 Nm (354 in-lb)
Handle Mounting Bolts: 8 Nm (71 in-lb)
Spark Plug: 20 Nm (177 in-lb)

Apply a drop of blue Loctite (243) to critical fasteners. Ensure all gaskets and seals are new and properly seated. Perform a functional test of all controls and the chain brake after reassembly.