stihl 660 workshop manual

The STIHL MS 660 is a professional-grade chainsaw featuring a high-performance engine, advanced anti-vibration system, and robust construction for demanding forestry and cutting applications. This workshop manual provides comprehensive technical information for service, maintenance, and repair procedures. Below are key sections covering safety, specifications, engine service, fuel system, ignition, clutch/chain brake, guide bar/chain, troubleshooting, and parts diagrams.

1. Safety Precautions & Symbols 2. Technical Specifications 3. Engine Disassembly & Assembly 4. Fuel System (Carburetor) 5. Ignition System 6. Clutch & Chain Brake 7. Guide Bar & Saw Chain 8. Anti-Vibration System 9. Troubleshooting Guide 10. Torque Specifications 11. Exploded Parts Views

Safety Precautions & Symbols

Always wear appropriate PPE (helmet, eye protection, gloves, chainsaw chaps, hearing protection). Ensure the chainsaw is stopped and cool before servicing. Disconnect the spark plug boot to prevent accidental starting. Use only genuine STIHL parts and specified tools.

Symbol	Meaning
⚠️	Warning - Risk of injury or damage
🔥	Fire hazard - Fuel/oil handling
⚡	Electrical hazard - Ignition system
🛠️	Special tool required
📏	Precise measurement needed

Technical Specifications

Model: STIHL MS 660
Engine Type: 2-stroke, single cylinder, air-cooled
Displacement: 91.6 cm³ (5.59 cu. in.)
Power Output: 6.4 kW (8.7 hp)
Fuel/Oil Mix: 50:1 (STIHL HP Ultra oil)
Idle Speed: 2,500 rpm
Max. Engine Speed: 13,500 rpm
Ignition System: Electronic, capacitor discharge
Spark Plug: Bosch WSR 6 F, NGK BPMR 7A (gap 0.5 mm)
Carburetor: STIHL HD-12 or HD-12A
Chain Oil Tank: 0.58 L
Fuel Tank: 0.82 L
Weight (powerhead): 7.4 kg (16.3 lbs)
Recommended Bar Lengths: 50 cm (20") to 90 cm (36")

Engine Disassembly & Assembly

Procedure for cylinder, piston, crankshaft, and bearings.

Remove top cover, air filter, and carburetor.
Remove muffler and spark plug.
Remove cylinder cover nuts; lift off cylinder.
Remove piston pin circlips; drive out piston pin.
Remove clutch and flywheel to access crankshaft.
Separate crankcase halves after removing all screws.
Inspect all components for wear, scoring, or damage.
Assembly is reverse order using new gaskets and seals.

WARNING! Mark crankcase halves for alignment. Use a torque wrench for assembly.

Fuel System (Carburetor)

HD-12/HD-12A carburetor adjustment and service.

Default screw settings (H, L, LA): Turn in gently until seated, then back out H=1 turn, L=1 turn, LA=1 turn.
Final adjustment requires tachometer: Set idle speed to 2,500 rpm; adjust LA for smooth idle.
High speed (H) adjustment: Max. 13,500 rpm under load.
Clean fuel filter, tank vent, and fuel lines annually.
Diaphragm kit replacement if engine runs lean or floods.

CAUTION! Do not overtighten adjustment screws. Use STIHL adjustment tool.

Ignition System

Testing and replacement of ignition module, spark plug, and stop switch.

Component	Test Procedure	Specification
Ignition Module	Resistance between spark plug connector and ground	Approx. 1.0 - 1.5 kΩ
Spark Plug	Visual inspection, gap check	0.5 mm (0.020 in)
Stop Switch	Continuity test (wire to ground)	Closed when pressed
Flywheel Air Gap	Check with feeler gauge	0.3 mm (0.012 in)

Tip: Always check for spark with plug grounded to cylinder.

Clutch & Chain Brake

Clutch drum, springs, shoes, and chain brake band service.

Remove clutch: Use STIHL clutch tool to hold piston; turn clutch nut clockwise (left-hand thread).
Inspect clutch shoes for wear; replace if worn to 50%.
Chain brake band: Check for wear, cracks, or glazing.
Test brake function: Hand guard should engage brake within 0.12 seconds at 2,500 rpm idle.
Lubricate clutch bearing with high-temperature grease.

WARNING! Never operate with a faulty chain brake. Replace entire assembly if damaged.

Guide Bar & Saw Chain

Maintenance, dressing, and replacement.

Bar Maintenance: Clean groove weekly; file rails if burred; rotate bar regularly.
Chain Sharpening: File angle 30°; depth gauge 0.65 mm below cutter.
Chain Tension: Correct when chain snaps back after lifting from bar.
Sprocket: Replace rim sprocket or drum sprocket when worn (matches chain pitch).
Oil Flow Check: Run at high idle; should see oil fling from chain.

CAUTION! Always use matching pitch/gauge for bar, chain, and sprocket.

Anti-Vibration System

AV springs and dampers inspection.

Check all four AV mounts (front and rear) for cracks, deterioration, or separation. Replace in sets if any mount is faulty. Ensure all bolts are torqued to specification.

Troubleshooting Guide

Symptom	Possible Cause	Corrective Action
Engine will not start	No spark, flooded, fuel issue	Check spark, plug wetness, fuel filter, carburetor diaphragms.
Engine starts then dies	Fuel tank vent, carburetor adjustment	Clean tank vent, adjust L and LA screws.
Loss of power	Clogged air filter, muffler screen, carburetor	Clean/replace filter, clean spark arrestor, check H screw.
Excessive vibration	AV mounts, unbalanced clutch/flywheel	Inspect AV system; check for bent crankshaft.
Chain does not oil	Clogged oil passages, faulty pump	Clean bar groove, check oil line, replace oil pump if needed.
Chain brake does not engage	Worn band, dirty mechanism	Clean and inspect band/mechanism; replace if worn.

Torque Specifications

Component	Torque (Nm)	Torque (ft-lbs)
Cylinder cover nuts	10-12	7.4-8.9
Crankcase screws	10-12	7.4-8.9
Clutch nut	40-50	29.5-36.9
Flywheel nut	40-50	29.5-36.9
Spark plug	20-25	14.8-18.4
Guide bar nuts	9-11	6.6-8.1
AV mount bolts	8-10	5.9-7.4

Note: Use a calibrated torque wrench. Apply thread locker where specified.

Exploded Parts Views

Refer to official STIHL parts catalog for detailed diagrams. Common assemblies: Engine group (1128), Fuel system (1140), Ignition (1116), Clutch/Chain brake (1135), AV system (1107). Always use part numbers when ordering.

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