Stihl MS 261, MS 261 C Service Repair Workshop Manual

STIH) STIHL MS 261 2010-05

1 MS 261, MS 261 C q © ANDREAS STIHL AG & Co. KG, 2010 RA_573_0_01_02 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 Torques 6 3. Troubleshooting 8 3.1 Clutch 8 3.2 Chain Drive, Chain Brake, Chain Tensioner 9 3.3 Chain Lubrication 11 3.4 Rewind Starter 12 3.5 Ignition System 14 3.6 Carburetor 15 3.7 Engine 18 4. Clutch 19 4.1 Clutch Drum 20 5. Chain Brake 21 5.1 Checking Operation 21 5.2 Brake Band 21 5.3 Brake Lever 23 5.4 Brake lever on machines with QuickStop Super 25 5.4.1 Adjusting the brake cable 27 5.4.2 Brake cable 28 5.5 Cam Lever 29 5.6 Pins 30 5.7 Chain Tensioner 32 5.7.1 Quick chain tensioner 32 5.8 Bar Mounting Studs 33 5.9 Collar Nuts for Sprocket Cover 34 6. Engine 35 6.1 Muffler 35 6.2 Leakage Test 36 6.2.1 Preparations 36 6.2.2 Vacuum Test 37 6.2.3 Pressure Test 37 6.3 Oil Seals 38 6.4 Shroud 39 6.5 Cylinder 40 6.6 Crankshaft 42 6.6.1 Bearings / Crankcase 47 6.7 Piston 48 6.8 Piston Rings 50 6.9 Decompression Valve 51 7. Ignition System 52 7.1 Ignition Timing 52 7.2 Preseparator 52 7.3 Install new Ignition Module 52 7.4 Testing the Ignition Module 54 7.5 Spark Plug Boot / Ignition Lead 56 7.6 Flywheel 57 7.7 Short Circuit Wire 58 7.7.1 Testing 58 7.7.2 Removing and Installing 58 7.7.3 Ground Wire 62 7.7.4 Contact Spring 62 7.8 Ignition System Troubleshooting 64 8. Rewind Starter 67 8.1 General 67 8.2 Fan housing 67 8.3 Pawls 68 8.4 ErgoStart 69 8.5 Rope Rotor 70 8.6 Starter Rope / Grip 71 8.7 Tensioning the Rewind Spring 73 8.8 Replacing the Rewind Spring 73 9. Servicing the AV System 76 9.1 Buffer on Oil Tank 76 9.2 AV Spring on Oil Tank 76 9.2.1 AV Spring on Oil Tank - Machines with Heating 76 9.3 AV Spring on Fuel Tank 77 9.4 AV Spring on Handlebar 78 9.4.1 Models with Heating 79 9.5 Stop Buffer at Clutch Side 79 9.5.1 Stop Buffer at Ignition Side 80 9.5.2 Buffers on Filter Base 80 9.6 Handlebar 81 9.6.1 Handlebar with Heating 82 10. Control Levers 87 10.1 Master Control Lever 87 10.1.1 Removing and Installing 87 10.2 Throttle Trigger/ Lockout Lever 87 10.3 Throttle Trigger/ Lockout Lever – QuickStop Super 89 10.3.1 Switch Lever – QuickStop Super 91 10.3.2 Lockout Lever – QuickStop Super 91 10.3.3 Choke Rod 92 10.3.4 Throttle Rod 93 11. Chain Lubrication 95 11.1 Pickup Body 95 11.2 Oil Suction Hose 95 11.3 Oil Pump 96 11.4 Valve 97 Contents

2 MS 261, MS 261 C Contents 12. Fuel System 98 12.1 Air Filter 98 12.2 Baffle 98 12.3 Filter Base 98 12.4 Air Guide Shrouds 100 12.4.1 Air Guide Shrouds – Models with Manual Fuel Pump 101 12.4.2 Air Guide Shrouds – Models with Heating 104 12.5 Carburetor 109 12.5.1 Leakage Test 111 12.6 Servicing the Carburetor 112 12.6.1 Metering Diaphragm 112 12.6.2 Inlet Needle 113 12.6.3 Pump Diaphragm 114 12.6.4 Levers on Throttle Shaft 115 12.6.5 Adjusting Screws 116 12.7 Adjusting the Carburetor 118 12.7.1 Basic Setting 118 12.7.2 Standard setting 119 12.8 Carburetor Carrier 120 12.9 Intake Manifold 121 12.10 Tank Vent 122 12.10.1 Testing 122 12.10.2 Removing and Installing 123 12.11 Fuel Intake 123 12.11.1 Pickup Body 123 12.11.2 Fuel Hose 124 12.11.3 Fuel Hose – Models with Manual Fuel Pump 125 12.11.4 Manual Fuel Pump 127 12.11.5 Tank Housing 128 13. Heating System 130 13.1 Carburetor Heating 130 13.1.1 Testing the Complete System 130 13.1.2 Testing the Heating Element 130 13.1.3 Thermostatic Switch 131 13.2 Carburetor Heating System Troubleshooting Chart 132 13.3 Handle Heating System 133 13.3.1 Troubleshooting 133 13.4 Heater Switch 133 13.5 Heating Element in Rear Handle 135 13.6 Heating Element in Handlebar 136 13.7 Generator 137 13.7.1 Handle Heating and Generator Troubleshooting Chart 139 13.7.2 Test Connections and Test Values 141 13.8 Wiring Harness 143 14. Special Servicing Tools 147 15. Servicing Aids 149

3 MS 261, MS 261 C 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 fault on the machine may have several causes. To help locate the fault, consult the troubleshooting charts for all assemblies and systems in this manual and the "STIHL Service Training System". 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 "STIHL 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: N Action to be taken as 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 a Direction of movement @ 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 1650 to the assembly stand with two screws (1) and washers. The screws must not project since they, depending on the machine, may damage housings when the machine is clamped in position. The above operation is not necessary with the new assembly stand 5910 890 3101 since the mounting plate is already fitted. Engage the bar mounting studs in the outer bores in the mounting plate and secure the machine in position with the M 8 nuts (arrows). 1 2 3 219RA000 TG 5902RA000 TG

4 MS 261, MS 261 C Machines with Quick Chain Tensioner Engage the bar mounting stud in the outer bore in the mounting plate and secure the machine in position with the M 8 nut (arrow). The machine is held in position on the mounting plate by the screw heads on the engine housing. Preparations for servicing Remove the chain sprocket cover, saw chain and guide bar before carrying out repairs or mounting the machine to the assembly stand. Always use original STIHL replacement parts. They can be identified by the STIHL part number, the { logo and the STIHL parts symbol K This symbol may appear alone on small parts. Storing and disposing of oils and fuels Collect fuel or lubricating oil in a clean container and dispose of it properly in accordance with local environmental regulations. 5902RA001 TG 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. Gasoline is an extremely flammable fuel and can be explosive in certain conditions. 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. 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. 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. Always perform leakage test after working on the fuel system and the engine. Always replace damaged parts. Check disassembled parts for wear or damage before re-installing – replace as necessary. Run the machine only with the shroud mounted in position – there is otherwise a risk of injury from the fanwheel and a risk of engine damage due to overheating. 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, b 15. Other press fluids are not approved and may result in damage to the fuel hoses. Coat the ends of the hoses and the connectors with STIHL press fluid and then push the new hoses on to the hose barbs, b 15.

5 MS 261, MS 261 C 2. Specifications 2.1 Engine MS 261 Displacement: 50.2 cm 3 Bore: 44.7 mm Stroke: 32.0 mm Engine power to ISO 7293: 2.8 kW (3.8 bhp) at 9,500 rpm Maximum permissible engine speed with bar and chain: 14,000 rpm Idle speed: 2,800 rpm Clutch: Centrifugal clutch without linings Clutch engages at: 3,600 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: as specified in instruction manual 2.3 Ignition System Air gap between ignition module and fanwheel: 0.20 (+ 0.1/- 0.05) mm Spark plug (resistor type): NGK BPMR 7 A BOSCH WSR6F Electrode gap: 0.5 mm 2.4 Chain Lubrication Speed-controlled oil pump with reciprocating piston and manual flow control Settings for oil delivery rate: min.: Ematic max.: 4.5 (+/2.0) cm 3 /min at 10,000 rpm 8.5 (+/3.0) cm 3 /min at 10,000 rpm 11.5 (+/3.0) cm 3 /min at 10,000 rpm

6 MS 261, MS 261 C 2.5 Tightening Torques 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. Fastener Thread size For component Torque Nm Remarks Screw P 4x12 Cover plate/sprocket cover (quick chain tensioner) 2.5 Screw M 4x8 Chain tensioner cover plate/crankcase 2.0 Screw P 5x16 Antivibration spring / handle housing 3.0 Screw M 4x16 Antivibration spring / crankcase 3.5 4) Screw M 4x12 Brake band/crankcase 3.0 1), 4) Screw P 4x10 Brake cable retainer/ tank housing (Q) 1.7 Collar screw M 8 Collar stud for bar 23.0 1) Collar screw M 8/M 10 Collar stud for bar (BE) 30.0 2) Screw M 4x12 Cover, chain brake/crankcase 3.0 4) M 10x1 Decompression valve 14.0 Screw M 4x9.6 Spark arresting screen/muffler 1.0 Screw M 12x0.75 Housing / switch (VW) 3.0 Screw M 4x12 Generator / crankcase (VW) 3.0 3) Screw P 6x32.5 Handlebar/tank housing 7.0 Screw P 6x30 Handlebar / tank housing (VW) 8.0 4) Screw M 6x26 Handlebar / bushing(VW) 8.0 2) Screw M 5x16 Handlebar / plug, antivibration spring (VW) 6.0 3), 4) Screw M 5x20 Hand guard/fan housing/crankcase 6.0 4) Screw P 6x30 Chain catcher/crankcase/bearing plug 8.0 Screw M 5x16 Spiked bumper / crankcase / upper locknut 8.0 3), 4) Lock nut M 5 Spiked bumper / crankcase / upper locknut 8.0 Screw M 5x16 Spiked bumper/crankcase, bottom 8.0 3), 4) Screw M 4x12 Manifold/cylinder 3.0 4) Screw M 5x25 Crankcase, sprocket side/fan side 10.0 4) Screw M 5x16 Bearing plug/cylinder 10.0 3), 4) Screw M 5x16 Fan housing/crankcase 6.0 4) Screw M 4x12 Air baffle/crankcase 1.5 4) Carrier M 12x1 L Carrier / crankshaft 50.0

7 MS 261, MS 261 C Fastener Thread size For component Torque Nm Remarks Screw M 4x12 Oil pump/crankcase 3.0 4) Screw M 5x16 Muffler/crankcase 10.0 3), 4) Screw M 5x16 Muffler / cylinder 10.0 3), 4) Nut M 8x1 Flywheel/crankshaft 28.0 5) Screw M 4x12 Thermostatic switch / carburetor (VW) 2.0 Collar nut M 5 Carburetor / collar screw, 1st stage, fan side 2.0 Collar nut M 5 Carburetor / collar screw, 2nd stage, sprocket side 3.5 Collar nut M 5 Carburetor / collar screw, 3rd stage, fan side 3.5 Screw M 5x16 Preseparator/crankcase 3.0 4) M 14x1.25 Spark plug 25.0 Screw M 4x20 Ignition module/crankcase 4.0 3) Screw M 5x20 Cylinder/crankcase, 1st stage 4.0 4) Screw M 5x20 Cylinder/crankcase, 2nd stage 10.0 4) Remarks: 1) Loctite 242 or 243, medium strength 2) Loctite 270, high strength 3) Micro-encapsulated screws 4) Screws with binding head 5) Degrease crankshaft/flywheel and mount oil-free VW) Carburetor and handle heating system Q) QuickStop Super BE) Quick chain tensioner/ErgoStart Use the following procedure when refitting a DG or P screw in an existing thread: Place the screw in the hole and rotate it counterclockwise until it drops down slightly. 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. Coat micro-encapsulated screws with medium strength Loctite 242 or 243 before reinstalling. Power screwdriver setting for polymer: DG and P 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.

8 MS 261, MS 261 C 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 rotates at idle speed Engine idle speed too high Readjust idle speed screw LA 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 261, MS 261 C 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 Clutch shoes badly worn Install new clutch Clutch drum badly worn Install new clutch drum Brake band blocked Check freedom of movement and operation of brake band Saw chain rotates at idle speed Engine idle speed too high Readjust idle speed screw LA Clutch springs stretched Replace the clutch springs or install new clutch Clutch springs broken Replace the clutch springs Saw chain does not stop immediately when brake is activated Brake spring stretched or broken Fit new brake spring Brake band stretched or worn Fit new brake band Clutch drum worn Install new clutch drum

Stihl MS 261, MS 261 C Service Repair Workshop Manual

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