Stihl MS 661 C-M User Manual

STIH)
STIHL MS 661, 661 C-M
2013-07

Stihl MS 661 C-M Specifications

General

Idle speed	- RPM
Motor type	2-stroke motor
Chain pitch	3/8 \
Blade length	800 mm
Product color	Black, Grey, Orange
Automatic oiling	Yes
Engine displacement	91.1 cm³
Power source	Gasoline
Sound power level	118 dB
Vibration emission	6.9 m/s²
Sound pressure level	105 dB

Weight and Dimensions

Weight	7400 g

Summary

Introduction and Safety Precautions

1.1 Introduction

Provides an overview of the service manual and guidance on its use for repair and servicing procedures.

1.2 Safety Precautions

Details essential safety regulations and precautions for performing maintenance and repair work on the equipment.

Specifications

2.1 Engine

Lists key engine specifications including displacement, bore, stroke, power output, and maximum permissible speed.

2.2 Fuel System

Specifies leakage test pressures and requirements for the fuel system components.

2.3 Ignition System

Details ignition system specifications like air gap, spark plug type, and electrode gap.

2.4 Chain Lubrication

Outlines the chain lubrication system and specifies oil delivery rates at different RPMs.

2.5 Tightening Torquese

Provides a list of fasteners with their specified torque values for various components.

Troubleshooting

3.1 Clutch

Troubleshooting guide for common clutch issues such as stopping under load or chain running at idle.

3.2 Chain Drive, Chain Brake, Chain Tensioner

Troubleshooting steps for issues related to the chain drive, chain brake, and chain tensioner.

3.3 Chain Lubrication

Troubleshooting guide for problems with the chain oil supply system.

3.4 Rewind Starter

Troubleshooting common issues with the rewind starter rope, spring, and mechanism.

3.5 Ignition System

Troubleshooting guide for ignition system faults like rough running, misfires, or irregular spark.

3.6 Carburetor

Troubleshooting common carburetor problems, including flooding, poor acceleration, and stalling.

3.7 Engine

Troubleshooting guide for engine starting difficulties, power loss, erratic running, and overheating.

Clutch

4.1 Clutch Drum

Instructions for removing, installing, and inspecting the clutch drum for signs of wear.

4.2 Clutch

Detailed procedure for disassembling and assembling the clutch assembly, including spring removal.

Chain Brake

5.1 Checking Operation

Procedure for checking the chain brake's safety function and braking time.

5.2 Brake Band

Steps for removing and installing the chain brake band, including inspection for wear.

5.3 Brake Lever

Procedure for removing and installing the brake lever mechanism and associated parts.

5.4 Cam Lever

Details on removing, installing, checking, and replacing the cam lever.

5.5 Pins

Instructions for inspecting and replacing anchor and pivot pins, ensuring square driving.

5.6 Chain Tensioner

Procedure for removing and installing the chain tensioner assembly.

5.7 Bar Mounting Studs

Instructions for removing and installing bar mounting studs using special tools.

5.8 Collar Nuts for Sprocket Cover

Procedure for replacing collar nuts on the sprocket cover using special tools.

Engine

6.1 Muffler

Instructions for removing, inspecting, and installing the muffler assembly.

6.2 Leakage Test

Procedure for performing vacuum and pressure tests to detect engine leaks.

6.2.1 Preparations

Steps required to prepare the engine for performing leakage tests.

6.2.2 Vacuum Test

Detailed instructions for conducting the engine vacuum test.

6.2.3 Pressure Test

Detailed instructions for conducting the engine pressure test.

6.3 Oil Seals

General information on replacing engine oil seals without full disassembly.

6.3.1 Ignition Side

Procedure for replacing the oil seal on the ignition side of the engine crankshaft.

6.3.2 Clutch Side

Procedure for replacing the oil seal on the clutch side of the engine crankshaft.

6.4 Shroud

Instructions for removing and installing the engine shroud.

6.5 Cylinder

Procedure for removing and installing the engine cylinder.

6.6 Crankshaft

Procedure for removing and installing the crankshaft assembly, including bearings.

6.6.1 Bearings / Crankcase

Information on replacing crankcase halves and associated bearings.

6.7 Piston

Procedure for removing and installing the engine piston.

6.8 Piston Rings

Instructions for removing, cleaning grooves, and installing piston rings.

6.9 Decompression Valve

Procedure for removing, checking, and installing the decompression valve.

Ignition System

7.1 Ignition Timing on All Models

Notes on fixed ignition timing and its immutability during repair procedures.

7.2 Ignition Module / Control Unit

Description of ignition module and control unit components and their basic testing.

7.3 Removing and Installing

Procedure for removing and installing the ignition module or control unit.

7.4 Testing the Ignition Module

Instructions for testing the ignition module using a spark test.

7.5 Spark Test

Guidance on performing spark tests using ZAT 4 and ZAT 3 ignition testers.

7.6 Spark Plug Boot / Ignition Lead

Procedure for removing and installing the spark plug boot and ignition lead.

7.7 Flywheel

Instructions for removing, inspecting, and installing the flywheel.

7.8 Testing Wiring Harness

Tests for checking wiring harness continuity and resistance between components.

7.9 Short Circuit Wire / without M-Tronic

Procedure for removing and installing the short circuit wire on non-M-Tronic models.

7.10 Short Circuit Wire / with M-Tronic

Procedure for removing and installing the short circuit wire on M-Tronic models.

7.11 Short Circuit Wire / with M-Tronic and Heating

Procedure for removing and installing the short circuit wire on M-Tronic models with heating.

7.12 Contact Spring

Instructions for removing and installing the contact spring assembly.

7.13 Ignition System Troubleshooting

Troubleshooting flowchart for diagnosing common ignition system faults.

M-Tronic

8.1 Calibrating the Control Unit

Procedure for calibrating the M-Tronic control unit after replacement or speed issues.

8.2 Testing with STIHL MDG 1

Instructions for testing the M-Tronic system using the STIHL MDG 1 analyzer.

8.3 Testing

General procedures for testing the M-Tronic system components.

8.4 Wiring Harness

Information on the M-Tronic and short circuit wire harness.

8.5 Switch Unit

Procedure for testing and replacing the switch unit.

8.6 Solenoid Valve

Procedure for removing, installing, and calibrating the solenoid valve.

8.7 M-Tronic Troubleshooting Chart

Troubleshooting flowchart for diagnosing M-Tronic system faults.

Rewind Starter

9.1 General

General notes on rewind starter operation, stiffness, and troubleshooting.

9.2 Rewind Starter Removing and Installing

Procedure for removing and installing the rewind starter assembly.

9.3 Pawls

Instructions for removing, installing, and checking the rewind starter pawls.

9.4 Rope Rotor

Procedure for relieving spring tension and working with the rope rotor.

9.5 Starter Rope / Grip

Instructions for replacing the starter rope and grip.

9.6 Tensioning the Rewind Spring

Procedure for correctly tensioning the rewind spring.

9.7 Replacing the Rewind Spring

Instructions for replacing the rewind spring.

9.8 Segment

Procedure for removing and installing the segment within the rewind starter.

AV Elements

10.1 Stop Buffer at Clutch Side

Procedure for removing and installing the stop buffer on the clutch side.

10.2 Antivibration Element on Oil tank / Tank Housing

Procedure for removing and installing antivibration elements on the oil tank and tank housing.

10.3 AV Element on Fuel Tank

Instructions for removing and installing the AV element on the fuel tank.

10.4 AV Element on Handlebar

Procedure for removing and installing AV elements on the handlebar.

10.4.1 Stop Buffer at Ignition Side

Procedure for removing and installing the stop buffer on the ignition side.

10.5 Handlebar

Instructions for removing and installing the handlebar.

10.5.1 Handlebar / Wrap Around Handlebar with Heating

Procedure for disconnecting electrical wires for heating system on wrap-around handlebars.

Control Levers

11.1 Switch Shaft

Procedure for removing and installing the switch shaft.

11.2 Throttle Trigger / Lockout Lever

Procedure for removing and installing the throttle trigger and lockout lever.

11.3 Throttle Rod

Instructions for removing and installing the throttle rod.

11.3.1 Choke Rod

Procedure for removing and installing the choke rod.

Chain Lubrication

12.1 Pickup Body

Instructions for removing and installing the oil pickup body.

12.2 Oil Suction Hose

Procedure for removing and installing the oil suction hose.

12.3 Oil Pump

Instructions for removing and installing the oil pump assembly.

12.3.1 Adjusting Uprated Oil Pumps

Guidance on adjusting oil pumps for increased oil flow rates.

12.4 Valve

Procedure for removing and installing the internal tank pressure equalization valve.

Fuel System

13.1 Air filter

Instructions for removing, checking, cleaning, and installing the air filter.

13.2 Baffle

Procedure for removing and installing the baffle.

13.3 Filter Base

Instructions for removing and installing the filter base.

13.4 Carburetor

Procedure for removing and installing the carburetor.

13.4.1 Leakage Test

Procedure for testing the carburetor for leaks using a pressure gauge.

13.5 Servicing the Carburetor

General guidelines and steps for servicing the carburetor.

13.5.1 Disassembling and Cleaning the Carburetor

Steps for disassembling and cleaning the carburetor.

13.5.2 Assembling the Carburetor

Instructions for assembling the carburetor after servicing.

13.5.3 Metering Diaphragm

Procedure for separating and checking the metering diaphragm and gasket.

13.5.4 Inlet Needle

Procedure for removing, checking, and installing the inlet needle.

13.5.5 Pump Diaphragm

Procedure for separating and checking the pump diaphragm and gasket.

13.5.6 Lever on Throttle Shaft

Instructions for removing and installing the lever on the throttle shaft.

13.5.7 Lever on Choke Shaft

Procedure for removing and installing the lever on the choke shaft.

13.5.8 Lever on Choke Shaft / Switch Unit, Models with M-Tronic

Instructions for removing and installing the lever and switch unit on M-Tronic models.

13.6 Adjusting the Carburetor, Models with M-Tronic

Notes on M-Tronic carburetor adjustment; manual adjustments are not necessary or possible.

13.7 Adjusting the Carburetor, Models without M-Tronic

Procedure for adjusting the carburetor on models without M-Tronic.

13.8 Adjusting the Carburetor

General guidance on carburetor adjustment procedures.

13.8.1 Basic Setting

Procedure for performing the basic setting of the carburetor after replacement or cleaning.

13.8.2 Setting

Steps for adjusting engine speeds using a tachometer or analyzer.

13.8.3 Standard Setting

Procedure for standard carburetor setting with and without limiter caps.

13.9 Manifold

Instructions for removing and installing the intake manifold.

13.9.1 Impulse Hose

Procedure for removing and installing the impulse hose.

13.10 Tank Vent

Procedure for testing and replacing the tank vent.

13.11 Fuel Intake

Information on fuel intake system components.

13.11.1 Pickup Body

Instructions for removing and installing the fuel pickup body.

13.11.2 Fuel Suction Hose in Tank Housing

Procedure for removing and installing the fuel suction hose in the tank housing.

13.11.3 Fuel Suction Hose on Carburetor

Instructions for removing and installing the fuel suction hose on the carburetor.

13.11.4 Tank Housing

Procedure for removing and installing the fuel tank housing.

Heating System

14.1 Carburetor Heating

Information and testing procedures for the carburetor heating system.

14.2 Carburetor Heating System Troubleshooting Chart

Flowchart for troubleshooting carburetor heating system issues.

14.3 Handle and Carburetor Heating System

Troubleshooting information for handle and carburetor heating systems.

14.4 Heater Switch

Procedure for removing, installing, and testing the heater switch.

14.5 Heating Element in Rear Handle

Information and testing for the heating element in the rear handle.

14.6 Heating Element in Handlebar

Information and testing for the heating element in the handlebar.

14.7 Generator

Procedure for removing and installing the generator.

14.7.2 Test Connections and Test Values

Table of test connections and expected values for heating system components.

14.8 Heating Element Connecting Wires

Information on connecting wires for heating elements.

14.8.1 Connecting Wire between Rear Handle and Handlebar

Procedure for connecting wires between rear handle and handlebar heating elements.

14.8.2 Connecting Wire between Rear Handle and Generator

Procedure for connecting wires between rear handle and generator.

Special Servicing Tools

Servicing Aids