Stihl 660 Magnum Workshop Manual

The Stihl 660 Magnum is a professional-grade chainsaw featuring a high-performance engine, advanced anti-vibration system, electronic ignition, automatic oiling, and decompression valve for easier starting. This workshop manual provides comprehensive technical information for service, maintenance, troubleshooting, and repair procedures. Below are key sections covering specifications, engine systems, fuel system, ignition, lubrication, troubleshooting, and safety guidelines.

1. Technical Specifications 2. Safety Precautions 3. Engine Overview 4. Fuel System 5. Ignition System 6. Lubrication System 7. Chain & Bar Assembly 8. Disassembly Procedures 9. Troubleshooting Guide 10. Maintenance Schedule 11. Parts List & Diagrams

Technical Specifications

Key technical data for the Stihl 660 Magnum chainsaw engine and components.

Specification	Description
Engine Type	2-stroke, single cylinder, air-cooled
Displacement	91.6 cc (5.59 cu. in.)
Power Output	7.4 hp (5.5 kW)
Fuel Capacity	825 ml (27.9 fl. oz.)
Oil Tank Capacity	360 ml (12.2 fl. oz.)
Chain Pitch	3/8" or .404"
Bar Length Range	20" to 36" (50 cm to 90 cm)
Weight (without bar/chain)	7.4 kg (16.3 lbs)
Ignition System	Electronic, CDI
Spark Plug	Bosch WSR6F or equivalent

Safety Precautions

Essential safety procedures before performing any workshop service.

Disconnect spark plug wire to prevent accidental starting.
Allow engine to cool completely before handling.
Work in a well-ventilated area away from open flames.
Use proper tools and personal protective equipment (PPE).
Secure chainsaw in a vise or holding fixture during service.

WARNING! Fuel and oil are flammable. Avoid sparks and heat sources. Always wear safety glasses and gloves.

Engine Overview

Detailed breakdown of the 2-stroke engine components and systems.

Cylinder & Piston: Inspect for scoring, wear, and ring condition.
Crankshaft & Bearings: Check for play and smooth rotation.
Decompression Valve: Test for proper sealing and operation.
Anti-Vibration System: Inspect rubber mounts and springs.
Cooling System: Clean fins and ensure airflow is unobstructed.

CAUTION! Engine components are precision parts. Handle with care to avoid damage.

Fuel System

Carburetor: Walbro HD-12A or equivalent; adjustable H, L, and idle screws.
Fuel Filter: In-tank filter; replace if clogged.
Fuel Lines: Check for cracks, leaks, and deterioration.
Fuel Tank Vent: Ensure vent is clear to prevent vacuum lock.
Fuel Mix Ratio: 50:1 (Stihl HP Ultra oil to unleaded gasoline).
Primer Bulb: Test for proper fuel delivery and no air leaks.

Ignition System

Components: Ignition coil (CDI), spark plug, stop switch, flywheel.

Testing: Check spark plug gap (0.5 mm / 0.020"). Test coil resistance: primary 0.1-0.2 Ω, secondary 8-10 kΩ. Inspect flywheel key for shearing.

Adjustments: Ignition timing is fixed; no adjustment required. Ensure air gap between coil and flywheel is 0.3 mm (0.012").

Lubrication System

Automatic chain oiler with adjustable flow rate. Manual oiler pump for additional lubrication.

Check oil pump drive gear and worm gear for wear.
Inspect oil lines for leaks or blockages.
Clean oil tank vent and filter.
Adjust oil flow via external screw (clockwise to decrease, counterclockwise to increase).

Tip: Use only Stihl chain oil or equivalent for proper lubrication and pump operation.

Chain & Bar Assembly

Proper installation, tensioning, and maintenance of guide bar and cutting chain.

Bar Installation: Align adjustment pin with hole in bar; secure with nuts.
Chain Installation: Ensure cutting teeth face forward on top of bar.
Tensioning: Adjust with tensioning screw until chain snaps back when lifted.
Sharpening: Use correct round file size (5.5 mm / 7/32") at 30° angle.
Depth Gauges: File to 0.65 mm (0.025") below cutting edge.
Sprocket: Inspect drive sprocket for wear; replace if worn.
Bar Maintenance: Clean bar groove; flip bar regularly for even wear.

WARNING! Always wear cut-resistant gloves when handling chain. Ensure chain brake is functional before operation.

Disassembly Procedures

Step-by-step guide for major component removal.

Remove top cover, air filter, and carburetor.
Remove clutch assembly and sprocket.
Separate engine from crankcase/handle assembly.
Remove cylinder head and piston.
Extract crankshaft and bearings.

Note: Tag and organize all parts. Refer to torque specifications during reassembly.

Troubleshooting Guide

Symptom	Possible Cause	Corrective Action
Engine will not start	No spark, flooded, fuel issue	Check spark, dry plug, verify fuel flow and mix.
Engine runs poorly/lacks power	Clogged filter, carb adjustment, air leak	Clean/replace filter; adjust carb; pressure test crankcase.
Excessive vibration	Worn AV mounts, unbalanced parts	Inspect and replace anti-vibration elements.
Chain does not oil	Blocked oil line, pump failure	Clean oil passages; inspect pump gears and diaphragm.
Overheating	Dirty cooling fins, lean fuel mix	Clean fins; check carb settings and fuel mix.

Maintenance Schedule

Regular service intervals to ensure optimal performance and longevity.

Daily: Clean air filter, check chain tension and sharpness.
Weekly: Inspect spark plug, clean cooling fins, check all fasteners.
Monthly: Clean fuel filter, inspect fuel lines, check clutch drum and sprocket.
Annually: Replace fuel filter, inspect piston/cylinder, check crankshaft seals.
As Needed: Sharpen chain, replace bar, service carburetor.

Parts List & Diagrams

Reference for genuine Stihl part numbers and assembly views.

Key part numbers (example): Cylinder - 1128 020 2005; Piston - 1128 030 2001; Carburetor Kit - 1128 007 1060; Ignition Module - 1128 400 1301.

Ordering: Use serial number for exact parts matching. Diagrams available in official Stihl IPL (Illustrated Parts List).

Support: For technical assistance and parts, contact authorized Stihl dealers or visit www.stihl.com.