STIHL MS 661, 661 C-M Chainsaw Service Repair Workshop Manual

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

1 MS 661, MS 661 C-M q © ANDREAS STIHL AG & Co. KG, 2013 RA_758_00_01_01 1. Introduction and Safety Precautions 3 1.1 Introduction 3 1.2 Safety Precautions 4 2. Specifications 5 2.1 Engine 5 2.2 Fuel System 5 2.3 Ignition System 5 2.4 Chain Lubrication 5 2.5 Tightening Torquese 6 3. Troubleshooting 8 3.1 Clutch 8 3.2 Chain Drive, Chain Brake, Chain Tensioner 9 3.3 Chain Lubrication 10 3.4 Rewind Starter 11 3.5 Ignition System 12 3.6 Carburetor 13 3.7 Engine 17 4. Clutch 18 4.1 Clutch Drum 18 4.2 Clutch 18 5. Chain Brake 19 5.1 Checking Operation 19 5.2 Brake Band 19 5.3 Brake Lever 20 5.4 Cam Lever 21 5.5 Pins 21 5.6 Chain Tensioner 22 5.7 Bar Mounting Studs 23 5.8 Collar Nuts for Sprocket Cover 23 6. Engine 24 6.1 Muffler 24 6.2 Leakage Test 25 6.2.1 Preparations 25 6.2.2 Vacuum Test 26 6.2.3 Pressure Test 26 6.3 Oil Seals 26 6.3.1 Ignition Side 26 6.3.2 Clutch Side 27 6.4 Shroud 28 6.5 Cylinder 28 6.6 Crankshaft 31 6.6.1 Bearings / Crankcase 35 6.7 Piston 36 6.8 Piston Rings 38 6.9 Decompression Valve 38 7. Ignition System 39 7.1 Ignition Timing on All Models 39 7.2 Ignition Module / Control Unit 39 7.3 Removing and Installing 39 7.4 Testing the Ignition Module 41 7.4.1 Testing Ignition Module with MDG 1 Engine Analyzer 41 7.5 Spark Test 42 7.6 Spark Plug Boot / Ignition Lead 43 7.7 Flywheel 44 7.8 Testing Wiring Harness 45 7.8.1 Testing Wiring Harness without M-Tronic 45 7.8.2 Testing Wiring Harness with M-Tronic 46 7.8.3 Testing Ground Wire 46 7.9 Short Circuit Wire / without M-Tronic Removing and Installing 46 7.10 Short Circuit Wire / with M-Tronic Removing and Installing 48 7.11 Short Circuit Wire / with M-Tronic and Heating Removing and Installing 50 7.12 Contact Spring 54 7.13 Ignition System Troubleshooting 57 8. M-Tronic 60 8.1 Calibrating the Control Unit 60 8.2 Testing with STIHL MDG 1 61 8.3 Testing 61 8.3.1 Preparations 61 8.3.2 Connecting Test Cables 62 8.3.3 Testing Screw and Plug Connections and Switch Contact 62 8.3.4 Checking the Solenoid Valve 63 8.3.5 Checking Detection of Start Conditions 64 8.3.6 Testing the Wiring Harness 65 8.4 Wiring Harness 66 8.5 Switch Unit 66 8.6 Solenoid Valve 68 8.7 M-Tronic Troubleshooting Chart 69 8.7.1 Circuit Diagram 69 8.7.2 Engine does not start 70 8.7.3 Engine does not start in position } 71 8.7.4 Engine speed drops under load – engine down on power 72 8.7.5 Ignition – no spark 73 8.7.6 Engine stops suddenly 74 8.7.7 Cut-off engine speed is not reached 75 9. Rewind Starter 76 9.1 General 76 9.2 Rewind Starter Removing and Installing 76 9.3 Pawls 76 9.4 Rope Rotor 77 9.5 Starter Rope / Grip 77 9.6 Tensioning the Rewind Spring 78 9.7 Replacing the Rewind Spring 78 9.8 Segment 79 Contents

2 MS 661, MS 661 C-M Contents 10. AV Elements 80 10.1 Stop Buffer at Clutch Side 80 10.2 Antivibration Element on Oil tank / Tank Housing 80 10.3 AV Element on Fuel Tank 81 10.4 AV Element on Handlebar 83 10.4.1 Stop Buffer at Ignition Side 83 10.5 Handlebar 83 10.5.1 Handlebar / Wrap Around Handlebar with Heating 85 11. Control Levers 88 11.1 Switch Shaft 88 11.1.1 Removing and Installing 88 11.2 Throttle Trigger / Lockout Lever 90 11.3 Throttle Rod 91 11.3.1 Choke Rod Models without M-Tronic 93 12. Chain Lubrication 94 12.1 Pickup Body 94 12.2 Oil Suction Hose 94 12.3 Oil Pump 94 12.3.1 Adjusting Uprated Oil Pumps 96 12.4 Valve 96 13. Fuel System 97 13.1 Air filter 97 13.2 Baffle 97 13.3 Filter Base 97 13.4 Carburetor 98 13.4.1 Leakage Test 101 13.5 Servicing the Carburetor 101 13.5.1 Disassembling and Cleaning the Carburetor 101 13.5.2 Assembling the Carburetor 102 13.5.3 Metering Diaphragm 102 13.5.4 Inlet Needle 103 13.5.5 Pump Diaphragm 104 13.5.6 Lever on Throttle Shaft 105 13.5.7 Lever on Choke Shaft 106 13.5.8 Lever on Choke Shaft / Switch Unit, Models with M-Tronic 106 13.6 Adjusting the Carburetor, Models with M-Tronic 107 13.7 Adjusting the Carburetor, Models without M-Tronic 107 13.7.1 Adjusting Screws 107 13.8 Adjusting the Carburetor 109 13.8.1 Basic Setting 109 13.8.2 Setting 109 13.8.3 Standard Setting 110 13.9 Manifold 111 13.9.1 Impulse Hose 112 13.10 Tank Vent 113 13.10.1 Testing 113 13.10.2 Removing and Installing 113 13.11 Fuel Intake 114 13.11.1 Pickup Body 114 13.11.2 Fuel Suction Hose in Tank Housing 114 13.11.3 Fuel Suction Hose on Carburetor 115 13.11.4 Tank Housing 115 14. Heating System 118 14.1 Carburetor Heating 118 14.1.1 Testing the Complete System 118 14.1.2 Testing the Heating Element 118 14.1.3 Thermostatic Switch 119 14.2 Carburetor Heating System Troubleshooting Chart 120 14.3 Handle and Carburetor Heating System 121 14.3.1 Troubleshooting 121 14.4 Heater Switch 122 14.5 Heating Element in Rear Handle 123 14.6 Heating Element in Handlebar 124 14.7 Generator 124 14.7.1 Handle Heating and Generator Trouble- shooting Chart 126 14.7.2 Test Connections and Test Values 128 14.8 Heating Element Connecting Wires 130 14.8.1 Connecting Wire between Rear Handle and Handlebar 130 14.8.2 Connecting Wire between Rear Handle and Generator 131 15. Special Servicing Tools 134 16. Servicing Aids 136

3 MS 661, MS 661 C-M 1. Introduction and Safety Precautions 1.1 Introduction This service manual contains detailed descriptions of all the repair and servicing procedures specific to this power tool. You should make use of the illustrated parts lists while carrying out repair work. They show the installed positions of the individual components and assemblies. Refer to the latest edition of the relevant parts list to check the part numbers of any replacement parts. A malfunction on the machine may have several causes. To help locate the problem, consult the chapter on "Troubleshooting" and the "STIHL Service Training System" for all assemblies. Refer to the “Technical Information” bulletins for engineering changes which have been introduced since publication of this service manual. Technical information bulletins also supplement the parts list until a revised edition is issued. The special tools mentioned in the descriptions are listed in the chapter on "Special Servicing Tools" in this manual. Use the part numbers to identify the tools in the "Special Tools" manual. The manual lists all special servicing tools currently available from STIHL. Symbols are included in the text and pictures for greater clarity. The meanings are as follows: In the descriptions: : = Action to be taken that is shown in the illustration (above the text) – = Action to be taken that is not shown in the illustration (above the text) In the illustrations: A Pointer (short arrow) aDirection of movement b 4.2 = Reference to another chapter, i.e. chapter 4.2 in this example. Service manuals and all technical information bulletins are intended exclusively for the use of properly equipped repair shops. They must not be passed to third parties. Servicing and repairs are made considerably easier if the machine is mounted to assembly stand (3) 5910 890 3100. To do this, secure the mounting plate (2) 5910 850 1651 to the assembly stand with two screws (1) and washers. The above operation is not necessary with the new assembly stand 5910 890 3101 since the mounting plate is already fitted. 1 2 3 1166RA444 TG 4 The screws must not project since they may, depending on the machine, damage housings when the machine is clamped in position, pack with washers (4) if necessary. Preparations for servicing The chain sprocket, saw chain and guide bar must be removed to mount the machine on the assembly stand for servicing. Engage the bar mounting studs in the lower holes in the mounting plate and secure the machine in position with the M 8 nuts (arrows). Always use original STIHL replacement parts. They can be identified by the STIHL part number, the STIH) logo and the STIHL parts symbol ( This symbol may appear alone on small parts. 1166RA001 TG

4 MS 661, MS 661 C-M Storing and disposing of fuels Collect fuel in a clean container and dispose of it properly in accordance with local environmental regulations. Connectors in electrical wires The insulating tube must be centered on the connector and completely cover it – there is otherwise a risk of a short circuit. The connector is properly assembled when its overall length is a = no more than 30 mm. Positioning wires Always use punch down tool 5910 890 4000 to press electrical wires fully into their guides. 1.2 Safety Precautions If the machine is started up in the course of repairs or maintenance work, observe all local and country- specific safety regulations as well as the safety precautions and warnings in the instruction manual. 5902RA299 TG a Fuel is extremely flammable and can be explosive in certain conditions. Do not smoke or bring any fire, flame or other source of heat near the fuel. All work with fuel must be performed outdoors only. Spilled fuel must be wiped away immediately. Avoid direct skin contact with fuel and avoid breathing in fuel vapor. Always perform leakage test after working on the fuel system and the engine. Exercise extreme caution while carrying out maintenance and repair work on the ignition system. The high voltages which occur can cause serious or fatal accidents. The ignition is switched on again automatically after the engine stops. The engine can start at any time if the rewind starter is operated. Always wear suitable protective gloves for operations in which components are heated for assembly or disassembly. Improper handling may result in burns or other serious injuries. Always replace damaged parts. Check disassembled parts for wear or damage before re-installing – replace as necessary. Run the machine only with the rewind starter and shroud mounted in position – there is otherwise a risk of injury from the flywheel and a risk of engine damage due to overheating. Remove the spiked bumper to reduce the risk of injury from contact with the sharp tips. The chapter on tightening torques lists all machine components that have to be tightened to a specific torque or coated with threadlocking adhesive. The specifications must be maintained when tightening down screws, nuts and other fasteners in all the procedures described in this service manual. Fuel system – hose barb connectors Pull off or push on fuel hoses in line with the connector, preferably by hand, to ensure the tightness of the fuel system. Avoid damaging the hose barb – do not use sharp-edged pliers, screwdrivers, etc. Do not cut open fuel hoses with a knife or similar tool. Do not re-use fuel hoses after removal. Always install new hoses – fuel hoses can be overstretched during removal. Install new fuel hoses either dry or with the aid of STIHL press fluid – coat the ends of hoses and the connectors, b 16. Other press fluids are not approved and may result in damage to the fuel hoses.

5 MS 661, MS 661 C-M 2. Specifications 2.1 Engine MS 661, MS 661 C-M Displacement: 91.1 cc Bore: 56.0 mm Stroke: 37.0 mm Engine power to ISO 7293: 5.4 kW (7.4 bhp) at 9,500 rpm Max. permissible speed (with cutting attachment): 1) 13,500 rpm 1) Idle speed: 2,800 rpm Clutch: Centrifugal clutch without linings Clutch engages at: 4,080 rpm Crankcase leakage test at gauge pressure: 0.5 bar under vacuum: 0.5 bar 2.2 Fuel System Carburetor leakage test at gauge pressure: 0.8 bar Operation of tank vent at gauge pressure: 0.5 bar Fuel: see instruction manual 2.3 Ignition System Air gap between ignition module and fanwheel: 0.30 (+ 0.05 / - 0.10) mm Spark plug (resistor type): NGK BPMR 7 A BOSCH WSR 6 F Electrode gap: 0.5 mm 2.4 Chain Lubrication Speed-controlled oil pump with reciprocating piston and manual flow control Standard / Uprated Standard Uprated (with pin driven home) Settings for oil delivery rate: min.: max.: max.: 7.0 (+/- 2.8) cc/min at 7,000 rpm 14.3 (+/- 2.5) cc/min at 7,000 rpm 18.9 (+/- 2.5) cc/min at 7,000 rpm 1) The engine reaches its maximum RPM and maximum power after the break-in period (5 to 10 tank fillings) – do not make any changes to the high speed screw (H) during the break-in period.

6 MS 661, MS 661 C-M 2.5 Tightening Torquese DG and P (Plastoform) screws are used in polymer and light metal components. These screws form a permanent thread when they are installed for the first time. They can be removed and installed as often as necessary without impairing the strength of the screwed assembly, providing the specified tightening torque is observed. For this reason it is essential to use a torque wrench. Use the following procedure when refitting a DG or P screw in an existing thread: Insert the screw in the hole and rotate it counterclockwise until it drops down slightly and engages in the existing thread. Tighten the screw clockwise to the specified torque. This procedure ensures that the screw engages properly in the existing thread and does not form a new thread and weaken the assembly. Micro-encapsulated screws and screws coated with threadlocking adhesive: Before re-installing, clean both threads (screw tap into female thread by hand and then blow out with compressed air; clean male thread with brush), coat micro-encapsulated screws with medium-strength Loctite 242 or 243, and screws previously coated with threadlocking adhesive with Loctite (see list of screws below). Power screwdriver setting for polymer: P and DG screws max. 500 rpm. Do not use an impact wrench for releasing or tightening screws. Do not mix up screws with and without binding heads. Fastener Thread size For component Torque Nm Remarks Screw M 4x8 Chain tensioner cover plate / crankcase 2.0 4) Screw P 6x40 Cover / handlebar / handle housing 6.0 M 8 Starter post / fan housing 12.0 5) Screw M 4x12 Brake band / crankcase 3.0 4), 5) Collar screw M 8 Collar screw / crankcase, for bar 23.0 2) Screw M 4x12 Cover, chain brake / crankcase 3.0 4), 6) M 10x1 Decompression valve 14.0 Screw M 4x10 Flange / crankcase 2.5 5) Nut M 12x0.75 Housing / heater switch 2.0 V, W Screw M 4x12 Generator / crankcase 3.0 V, W, 5) Collar screw M 6x26 Handlebar / PA6 bushing 6.0 Screw P 6x40 Handlebar holder / handlebar / handle housing 6.0 Screw M 5x40x25 Hand guard / fan housing / crankcase 7.0 4), 6) Nut M 5 Shroud / stud, cylinder 3.0 Nut M 6 Spiked bumper (chain catcher) 6.0 Locknut M 5 Spiked bumper / chain sprocket cover 6.0 Screw M 5x12 Spiked bumper / chain sprocket cover / nut 6.0 Screw M 5x12 Spiked bumper / crankcase, top 8.0 4), 6) Locknut M 5 Spiked bumper / crankcase, top / nut 8.0

7 MS 661, MS 661 C-M Fastener Thread size For component Torque Nm Remarks Screw M 5x20 Spiked bumper / crankcase, bottom 8.0 5) Collar screw M 6x50 Spiked bumper / nut (chain catcher) 6.0 5) Screw M 5x20 Crankcase, sprocket side/fan side 10.0 4), 6) Screw P 5x16 Bearing plug AS1 / crankcase 4.0 Screw M 5x16 Bearing plug AS2 / handlebar 6.0 4), 5) Screw M 5x16 Bearing plug AS2 / cylinder 10.0 4), 5) Screw P 5x16 Bearing plug ZS3 / crankcase 4.0 Screw M 5x20 Fan housing / crankcase 7.0 4), 6) Screw M 4x12 Fan housing / winter cover plate 2.0 5) Carrier M 13x1 L Carrier / crankshaft 70.0 Screw M 4x12 Oil pump / crankcase 3.0 4), 5) Screw M 4x10 Ground wire cable lug / crankcase 2.5 4), 5) Screw P 4x10 M-Tronic cable lug / handle housing 1.5 Screw P 4x10 Heater cable lug / handle housing 1.5 V, W Screw M 5x20 Muffler / crankcase 10.0 4), 5), 6) Screw M 5x30 Muffler / cylinder 10.0 3), 4), 6) Screw M 5x6 Muffler casing, top 6.0 4), 5) Screw M 4x12 Switch unit / carburetor 2.0 5) Screw P 4x10 Guard / handle housing 1.5 Nut M 10x1 Flywheel / crankshaft 45.0 7) Screw M 4x8 Side plate / crankcase 2.0 4) Screw M 3x20 Manifold clamp / cylinder 0.5 Screw M 4x20 Ignition module / control unit / crankcase 4.0 5) Stud M 5 Stud / cylinder 8.0 5) Screw 6-32 UNCx11.5 Thermostatic switch / carburetor cover 1.1 V Screw M 3x4.5 Solenoid valve / carburetor 0.7 Collar nut M 5 Carburetor 3.5 Screw P 6x40 Elbow connector / handle housing 6.0 Screw M 5x16 Elbow connector / handlebar 7.0 4), 6) M 14x1.25 Spark plug 25.0 Screw M 6x30 Cylinder / crankcase 15.0 4), 6) Remarks: 1) Loctite 242 or 243, medium strength 2) Loctite 270, high strength 3) Loctite 272, high strength up to 250°C 4) Screws with binding head 5) Micro-encapsulated screws 6) Waxed screws 7) Degrease crankshaft / flywheel and mount oil-free W) Heated handles V) Carburetor heating

8 MS 661, MS 661 C-M 3. Troubleshooting 3.1 Clutch Condition Cause Remedy Saw chain stops under full load Clutch shoes badly worn Install new clutch Clutch drum badly worn Install new clutch drum Saw chain runs while engine is idling Engine idle speed too high Depending on model: Readjust idle speed screw LA or check M-Tronic Clutch springs stretched Replace the clutch springs or install new clutch Clutch springs broken Replace the clutch springs Loud noises Clutch springs stretched Replace all clutch springs Needle cage damaged Fit new needle cage Clutch shoe retainer broken Install new retainer or clutch Clutch shoes and carrier worn Install new clutch

9 MS 661, MS 661 C-M 3.2 Chain Drive, Chain Brake, Chain Tensioner Condition Cause Remedy Chain sprocket wears rapidly Chain not properly tensioned Tension chain as specified Wrong chain pitch Fit chain of correct pitch Insufficient chain lubrication Check chain lubrication Saw chain stops under full load Brake band blocked Check freedom of movement and operation of brake band Saw chain does not stop immediately when brake is activated Chain brake spring stretched / broken Fit new brake spring Brake band stretched / worn / broken Fit new brake band Clutch drum worn Install new clutch drum

STIHL MS 661, 661 C-M Chainsaw Service Repair Workshop Manual

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