MS 660 STIHL Manual

The STIHL MS 660 is a professional-grade chainsaw designed for heavy-duty felling, limbing, and bucking applications. It features a high-performance engine with advanced anti-vibration system, QuickStop® inertia chain brake, decompression valve for easier starting, STIHL Ematic™ lubrication system, and a range of safety features. Below are key sections for safety, features, operation, maintenance, and troubleshooting.

Features at a Glance

Key components: High-torque engine, anti-vibration system, QuickStop® chain brake, side-access chain tensioner, STIHL Ematic™ lubrication, and decompression valve.

Feature	Description
Engine Displacement	91.6 cc two-stroke engine
Power Output	6.4 kW (8.7 hp)
Guide Bar Lengths	Recommended 20" to 36"
Weight (powerhead)	Approx. 7.4 kg (16.3 lbs)
Fuel Tank Capacity	825 ml (27.9 fl. oz)
Oil Tank Capacity	410 ml (13.9 fl. oz)
Ignition System	Electronic ignition (CDI)
Anti-Vibration System	Spring-mounted handles
Chain Brake	QuickStop® inertia-activated
Decompression Valve	Reduces starting effort

Safety Instructions

Read all instructions before operation. Always wear proper PPE.

1. Personal Protective Equipment: Wear safety glasses, hearing protection, gloves, chainsaw chaps, and sturdy boots.
2. Work Area Safety: Clear area of obstacles; ensure secure footing; keep bystanders away.
3. Chain Brake: Test before each use; engage when carrying or moving short distances.
4. Kickback Awareness: Avoid contact with bar nose; maintain secure grip.

WARNING! Chainsaw operation is hazardous. Failure to follow safety instructions can result in serious injury or death.

Assembly & Preparation

Assemble guide bar and chain; fill with fuel and oil.

1. Attach Guide Bar: Remove bar cover nuts; position bar on studs; adjust chain tension.
2. Install Chain: Place chain on sprocket and bar groove; ensure cutting teeth face forward.
3. Fuel Mix: Use 50:1 gasoline to STIHL HP Ultra two-stroke oil. Do not use automotive oil.
4. Chain Oil: Use STIHL chain oil or approved substitute; fill oil tank.
5. Check Controls: Ensure throttle trigger, throttle lockout, and chain brake function properly.

CAUTION! Fuel is highly flammable. Refuel in well-ventilated area with engine off and cool.

Technical Specifications

• Engine Type: Single cylinder, two-stroke, air-cooled.
• Displacement: 91.6 cc.
• Power Output: 6.4 kW at 9,500 rpm.
• Max Engine Speed: 13,500 rpm.
• Idle Speed: 2,800 rpm.
• Fuel/Oil Ratio: 50:1 (STIHL HP Ultra).
• Ignition: Electronic, capacitor discharge.
• Spark Plug: Bosch WSR 6 F or equivalent.
• Sound Pressure Level: Approx. 112 dB(A).
• Vibration Levels: Front handle 4.2 m/s²; rear handle 3.8 m/s².

Controls and Components

Main components: Front handle with chain brake, rear handle, throttle trigger, throttle lockout, master control lever, decompression valve, and fuel/oil caps.

Master Control Lever: Combines choke, start, and run positions.

Chain Brake Handle: Front hand guard; activates brake when pushed forward.

Decompression Valve: Button to reduce cylinder pressure for easier starting.

Side-Access Tensioner: Tool-free chain adjustment via dial on side.

Starting & Stopping

Cold Start Procedure:

1. Engage chain brake.
2. Press decompression valve (if equipped).
3. Set master control lever to choke position (full down).
4. Press fuel primer bulb 5-10 times until fuel is visible.
5. Place saw on ground, hold rear handle with right foot.
6. Pull starter handle sharply until engine fires.
7. Move master control lever to half-throttle position.
8. Pull starter until engine starts.
9. Briefly blip throttle to disengage start position.

Stopping: Release throttle; push master control lever up to STOP position.

Operating Instructions

Proper cutting techniques for felling, limbing, and bucking.

1. Felling: Plan escape path; make notch cut; make felling cut; use wedges if needed.
2. Limbing: Stand uphill; cut from trunk outward; avoid cutting with bar tip.
3. Bucking: Support log properly; cut from top side; avoid pinching bar.
4. Kickback Prevention: Maintain firm grip; do not cut with upper quadrant of bar nose.
5. Chain Lubrication: Check oil flow regularly; adjust oiler as needed.

Tip: Keep chain sharp; a dull chain increases effort and risk of kickback.

Maintenance Schedule

Daily/Before Use: Check chain tension, sharpness, and lubrication; inspect bar for wear; clean air filter; check all fasteners.

Weekly: Clean spark arrestor screen; check fuel filter; inspect spark plug.

Monthly: Clean cooling fins; check anti-vibration elements; inspect clutch and sprocket.

Annually: Have professional service including cylinder inspection, carburetor adjustment, and bearing checks.

Chain & Bar Care

Chain Sharpening: Use correct round file size (typically 7/32" or 5/16"); maintain 30° cutting angle; file all cutters evenly.

Bar Maintenance: Clean bar groove regularly; flip bar weekly for even wear; dress bar rails if burred.

Chain Tension: Adjust when cold; chain should snap back when pulled from bar.

CAUTION! Always wear gloves when handling chain. Disconnect spark plug before maintenance.

Storage Guidelines

Long-term Storage (over 30 days):

1. Drain fuel tank and run engine until it stops.
2. Remove spark plug; add 1-2 teaspoons of oil to cylinder; pull starter 2-3 times; reinstall plug.
3. Clean entire saw; remove chain and bar; coat with oil.
4. Store in dry, cool place away from ignition sources.

WARNING! Never store with fuel in tank for extended periods; fuel can degrade and damage engine.

Troubleshooting

Symptom	Possible Cause	Corrective Action
Engine won't start	No spark/flooded/old fuel	Check spark plug; use fresh fuel mix; follow cold start procedure.
Engine runs poorly	Dirty air filter/clogged fuel filter	Clean/replace air filter; replace fuel filter.
Chain doesn't turn	Brake engaged/clutch worn	Disengage chain brake; inspect clutch shoes and drum.
Excessive vibration	Loose components/worn AV mounts	Tighten all fasteners; check anti-vibration elements.
Chain throws oil	Over-oiling/wrong oil viscosity	Adjust oiler setting; use recommended chain oil.
Chain dulls quickly	Cutting dirty wood/improper filing	Avoid cutting ground-contact wood; sharpen correctly.

Service: For repairs beyond basic maintenance, contact authorized STIHL servicing dealer.

Support: STIHL Incorporated, 1-800-467-8445, www.stihlusa.com