STIHL Series 4144 Powerhead Trimmers (FS 40/FS 50/FS 56/FC 56/KM 56) OEM Service & Repair Manual

STIH) STIHL Series 4144 Components FC, FS, KM 2008-02 FS 40, FS 50, FS 56 FC 56 KM 56

1 Series 4144 Components FC, FS, KM q © ANDREAS STIHL AG & Co. KG, 2008 RA_545_01_01_01 1. Introduction 2 2. Safety Precautions 3 3. Specifications 4 3.1 Engine 4 3.2 Fuel System 4 3.3 Ignition System 4 3.4 Tightening Torquese 5 4. Troubleshooting 7 4.1 Clutch 7 4.2 Rewind Starter 8 4.3 Ignition System 9 4.4 Carburetor 11 4.5 Engine 14 5. Engine 15 5.1 Removing and Installing 15 5.2 Leakage test 16 5.3 Oil seals 16 5.4 Ignition Module / Spark Plug Boot 16 5.5 Clutch 16 5.6 Flywheel 16 5.7 Motor 16 5.8 Muffler / Spark Arresting Screen 19 5.9 Short Circuit Wire 20 5.9.1 Testing 20 5.9.2 Removing and Installing (Loop Handle Version) 20 5.9.3 Removing and Installing (Bike Handle Version) 23 5.9.4 Ground Wire 26 5.10 Ignition System Troubleshooting 27 6. Rewind Starter 30 6.1 General 30 6.2 Removing and Installing 30 6.3 Pawls 30 6.3.1 Carrier 31 6.4 Rope Rotor 32 6.5 Starter Rope / Grip 33 6.6 Tensioning the Rewind Spring 35 6.7 Replacing the Rewind Spring 36 6.8 ErgoStart 36 7. Control Levers 37 7.1 Switch Shaft / Control Lever 37 7.2 Switch Positions 37 7.3 Interlock Lever (Loop Handle) 37 7.3.1 Throttle Trigger 38 7.4 Throttle Trigger/ Interlock Lever (Bike Handle) 40 7.5 Handlebar (Bike Handle) 43 8. Fuel System 44 8.1 Air Filter 44 8.1.1 Baffle 44 8.1.2 Filter housing 44 8.2 Removing and Installing the Carburetor 45 8.3 Leakage Test 47 8.4 Servicing the Carburetor 47 8.4.1 Metering Diaphragm / Manual Fuel Pump 47 8.4.2 Inlet Needle 49 8.4.3 Pump Diaphragm 49 8.4.4 Throttle Lever / Rotary Knob 51 8.4.5 Adjusting Screws 52 8.5 Adjusting the Carburetor 54 8.5.1 Basic Setting 54 8.5.2 Standard Setting 55 8.6 Removing and Installing Throttle Cable (Loop Handle) 56 8.6.1 Removing and Installing Throttle Cable (Bike Handle) 58 8.6.2 Adjusting the Throttle Cable 58 8.7 Removing and Installing the Spacer Flange 59 8.8 Tank Vent 60 8.8.1 Testing 60 8.8.2 Removing and Installing 61 8.9 Fuel Intake 61 8.9.1 Pickup Body 61 8.9.2 Fuel Hoses 62 8.9.3 Fuel Tank Cap 63 8.10 Removing and Installing the Engine Housing 64 9. Drive Tube 65 9.1 Removing and Installing 65 9.1.1 Disassembling (KM 56) 66 9.1.2 Disassembling (FC 56) 68 9.1.3 Disassembling (FS 56) 69 9.1.4 Disassembling (FS 40, 50) 70 9.1.5 Removing and Installing the Bearing Housing 71 9.1.6 Loop Handle 72 9.1.7 Loop Handle with Barrier Bar 73 9.2 Add-On Components 74 9.2.1 Deflector for Machines without Gearbox 74 9.2.2 Deflector for Machines with Gearbox 74 9.2.3 One-part Carrying Ring 75 9.2.4 Retainer 75 9.3 Gearbox 75 10. Special Servicing Tools 76 11. Servicing Aids 77 Contents

2 Series 4144 Components FC, FS, KM 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: : = 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 aDirection 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. 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.

3 Series 4144 Components FC, FS, KM 2. Safety Precautions If the engine 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. 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.

4 Series 4144 Components FC, FS, KM 3. Specifications 3.1 Engine FS 40 FS 50, 56, FC 56, KM 56 Displacement: 27.2 cm 3 27.2 cm 3 Bore: 34 mm 34 mm Stroke: 30 mm 30 mm Engine power to ISO 8893: 0.7 kW (1.0 bhp) at 8,500 rpm 0.8 kW (1.1 bhp) at 8,500 rpm Max. permissible speed (with cutting attachment): 10,000 rpm 10,000 rpm Idle speed: 2,800 rpm 2,800 rpm Clutch: Centrifugal clutch without linings Centrifugal clutch without linings Clutch engages at: 4,200 rpm 4,200 rpm Crankcase leakage test at gauge pressure: 0.5 bar under vacuum: 0.5 bar 3.2 Fuel System Carburetor leakage test at gauge pressure: 0.3 bar Operation of tank vent at gauge pressure: 0.5 bar Fuel: as specified in instruction manual 3.3 Ignition System Air gap between ignition module and fanwheel: 0.30 mm Spark plug (suppressed): NGK CMR6H NGK 6H Bosch WSR 6 F Electrode gap: 0.5 mm

5 Series 4144 Components FC, FS, KM 3.4 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. Fastener Thread size For component Torque Nm Remarks Screw P 6x14 Line limiting blade/deflector 2.5 Screw M 5x30 Control handle/handle/nut with washer 2.0 Screw P 5x14 Filter cover/filter housing 3.0 Nut M 5 Filter housing/carburetor/spacer flange 3.5 Screw P 4x12 Throttle cable/engine housing 1.5 Screw D 6x28 Gearbox/drive tube clamp (FS 56) 12.0 Screw D 5x20 Shroud/cylinder 6.0 Screw M 6x35 Clamp/clamp block/clamp 4.5 Screw M 6x25 Clamp/loop handle 4.5 Screw P 5x20 Engine housing/shroud 4.0 Screw M 5x20 Engine housing/crankcase 7.0 Screw P 5x20 Engine housing torsion lock/drive tube 4.0 Screw M 5x14 Deflector/gearbox (FS 56) 4.5 Screw M 6x30 Deflector/drive tube/nut /FS 40,50) 5.0 Screw M 6x14 Clamp/drive tube/harness ring 4.5 Screw D 5x20 Starter cover/crankcase 6.0 Screw D 5x20 Starter cover/engine pan 6.0 Screw M 4x9 End cover/carburetor 2.0

6 Series 4144 Components FC, FS, KM Remarks: 1) Loctite 242 or 243, medium strength 2) Loctite 270, high strength 3) Loctite 649, high strength 4) Loctite 272, high strength up to 250°C 5) Degrease crankshaft/flywheel and mount oil-free 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.

7 Series 4144 Components FC, FS, KM 4. Troubleshooting 4.1 Clutch Condition Cause Remedy Cutting attachment stops under load at full throttle Clutch shoes badly worn Install new clutch Clutch drum badly worn Install new clutch drum Cutting attachment runs at idle speed Engine idle speed too high Readjust idle speed screw LA Clutch springs stretched or fatigued Replace the clutch springs or install new clutch Clutch spring hooks broken Replace the clutch springs Loud noises Clutch springs stretched or fatigued Replace all clutch springs Clutch shoe retainer broken Install new clutch Clutch shoes and carrier worn Install new clutch Condition Cause Remedy

8 Series 4144 Components FC, FS, KM 4.2 Rewind Starter Condition Cause Remedy Starter rope broken Rope pulled out too vigorously as far as stop or over edge, i.e. not vertically Fit new starter rope Normal wear Fit new starter rope Starter rope does not rewind Very dirty or corroded Clean rewind spring or replace rope rotor Insufficient spring tension Check rewind spring and increase tension Rewind spring broken Install new rope rotor Starter rope cannot be pulled out far enough Spring overtensioned Check rewind spring and reduce tension Starter rope can be pulled out almost without resistance (crankshaft does not turn) Guide pegs on pawls or pawls themselves are worn Fit new pawls Spring clip on pawl fatigued Fit new spring clip Starter rope is difficult to pull or rewinds very slowly Starter mechanism is very dirty Thoroughly clean complete starter mechanism Lubricating oil on rewind spring becomes viscous at very low outside temperatures (spring windings stick together) Coat rewind spring with a little standard solvent-based degreasant (containing no chlorinated or halogenated hydrocarbons), then pull rope carefully several times until normal action is restored

9 Series 4144 Components FC, FS, KM 4.3 Ignition System 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. Condition Cause Remedy Engine runs roughly, misfires, temporary loss of power Spark plug boot is loose Press boot firmly onto spark plug and fit new spring if necessary Spark plug sooted, smeared with oil Clean the spark plug or replace if necessary. If sooting keeps recurring, check air filter Fuel/oil mixture – too much oil Use correct mixture of fuel and oil Incorrect air gap between ignition module and flywheel Set air gap correctly Flywheel cracked or has other damage or pole shoes have turned blue Install new flywheel Ignition timing wrong, flywheel out of adjustment, key on crankshaft has sheared off Locate flywheel properly or install new flywheel Weak magnetization in flywheel Install new flywheel Irregular spark Check operation of switch shaft/ contact springs and ignition module. Faulty insulation or break in ignition lead or short circuit wire. Check ignition lead/ignition module and replace ignition module if necessary. Check operation of spark plug. Clean the spark plug or replace if necessary. Crankcase damaged (cracks) Install new crankcase

STIHL Series 4144 Powerhead Trimmers (FS 40/FS 50/FS 56/FC 56/KM 56) OEM Service & Repair Manual

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