Stihl FS 36, FS 40, FS 44 Brushcutters Full Service & Repair Manual

STIHL FS 36, 40, 44 1 Service Manual FS 36, FS 40 and FS 44 Brushcutters 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. Microfilmed parts list are always more up to date than printed lists. A fault on the machine may have several causes. Consult the "troubleshooting charts" when tracing faults. Refer to the "Technical Information Bulletins" for engineering changes which have been introduced since publication of this service manual. The STIHL Special Tools manual lists all special servicing tools currently available from STIHL. Always use original STIHL replacement parts. Original STIHL parts can be identified by the STIHL part number, the STIHl logo and the STIHL parts symbol ( The symbol may appear alone on small parts. STIHl Service manuals and technical information bulletins describing engineering changes are intended exclusively for the use of STIHL servicing dealers and staff and must not be passed on to third parties.

STIHL FS 36, 40, 44 2 CONTENTS 1. Specifications 3 1.1 Engine 3 1.2 Fuel System 4 1.3 Ignition System 4 1.4 Gearhead 5 1.5 Weights 5 1.6 Special Accessories 5 1.6.1 For User 5 1.6.2 For Service Shop 5 1.7 Tightening Torques 6 2. Troubleshooting Charts 8 2.1 Clutch 8 2.2 Engine 8 2.3 Ignition System 9 2.4 Rewind Starter 10 2.5 Fuel System 11 3. Clutch 13 3.1 Disassembly 13 3.2 Assembly 15 4. Engine 17 4.1 Removing and Refitting Exhaust Muffler 17 4.2 Exposing the Cylinder 18 4.3 Cylinder and Piston 19 4.3.1 Removal 19 4.3.2 Installation 20 4.4 Piston Ring 21 4.5 Crankcase 21 4.5.1 Removing and Installing the Crankshaft 21 4.5.2 Ball Bearings and Oil Seal 22 4.6 Leakage Testing the Crankcase 24 4.6.1 Preparations 25 4.6.2 Pressure Test 26 4.6.3 Vacuum Test (for Diaphragm) 27 4.6.4 Vacuum Test (for Oil Seal) 28 5. Ignition System 29 5.1 Repairing Component Parts 29 5.1.1 Spark Plug 29 5.1.2 Ignition Module 31 5.1.2.1 Ignition Timing 31 5.1.2.2 Removing and Installing 31 5.1.3 Contact Spring (FS 36 and FS 40) 32 5.1.4 Flywheel 32 5.1.5 Spark Plug Terminal 33 5.1.6 Short Circuit Wire (FS 44) 34 6. Rewind Starter 35 6.1 Routine Maintenance 35 6.2 Replacing the Starter Rope (with Fan Housing Fitted) 35 6.3 Tensioning the Rewind Spring (with Fan Housing Fitted) 36 6.4 Rope Rotor 37 6.4.1 Removal 37 6.4.2 Installation 38 6.4.3 Tensioning the Rewind Spring (with Fan Housing Removed) 39 6.5 Replacing the Rewind Spring 39 6.6 Starter Pawls 40 7. Throttle Control 41 7.1 Throttle Trigger (FS 36, FS 40) 41 7.2 Throttle Trigger, Throttle Trigger Interlock, Stop Switch (FS 44) 42 7.2.1 Disassembly 42 7.2.2 Assembly 43 7.3 Throttle Trigger, Throttle Trigger Inter- lock (FS 44 with Two- Handed Handlebar) 44 7.4 Contact Springs in Control Handle (FS 44 with Two-Handed Handlebar) 45 7.5 Handle Support 46 7.6 Throttle Cable 47 8. Fuel System 48 8.1 Air Filter 48 8.2 Leakage Testing the Carburetor 48 8.3 Removing the Carburetor 50 8.4 Servicing the Carburetor 50 8.5 Carburetor Adjustment 56 8.6 Diaphragm Carrier, Diaphragm 58 8.7 Pickup Body and Fuel Hose 59 8.8 Fuel Tank 60 8.9 Tank Vent 60 8.10 Fuel Pump 61 9. AV System (FS 40 and FS 44) 62 9.1 Repair 62 10. Cutting Tool Drive 63 10.1 Bearing Housing (FS 36, FS 40) 63 10.2 Gearhead (FS 44) 65 10.2.1 Disassembly 65 10.2.2 Assembly 66 10.3 Drive Shaft 68 10.4 Drive Tube 69 11. Special Servicing Tools and Aids 71 11.1 Special Servicing Tools 71 11.2 Servicing Aids 72

STIHL FS 36, 40, 44 3 1. SPECIFICATIONS STIHL single-cylinder two-stroke engine with special impregnated cylinder bore. Displacement: Bore: Stroke: Power output: Max. permissible engine speed without cutting tool: Cut-out speed without cutting tool: Idle speed: Bearings: Rewind starter: Remaining pull on rope rotor: Pawl/flywheel clearance: Starter rope: Clutch: Clutch engages at: Crankcase leakage test at gauge pressure: under vacuum: Silencing: 30.2 cm 3 (1.84 cu. in) 34.8 mm (1.36 in) 31.8 mm (1.25 in) 0.7 kW (0.95 bhp) 10,000 rpm 9,300 rpm (± 700 rpm) 3,100 rpm Crankshaft supported in heavy-duty ball bearings; needle cages at big and small ends Pawl system with automatic starter rope rewind 1/4 to 1 3/4 turns 0.05-0.4 mm (0.002-0.016 in) 3.5 mm (0.14 in) dia. x 850 mm (33.5 in) Centrifugal clutch without linings 4,000 rpm (± 500 rpm) 0.5 bar (7.25 psi) 0.4 bar (5.8 psi) Intake air silencer and exhaust muffler 1.1 Engine

STIHL FS 36, 40, 44 4 Carburetor: Basic setting High speed adjusting screw H: Low speed adjusting screw L: Carburetor leakage test at gauge pressure: Fuel tank capacity: Fuel mixture: Octane number: Mix ratio: Air filter: Type: Air gap: Ignition timing: Spark plug (suppressed): Electrode gap: Spark plug thread: Length of thread: Heat range: All-position diaphragm carburetor with integral fuel pump Back off approx. 1 turn (only for service shop) Back off approx. 1 turn (Basic setting with screws initially moderately tight against their seats) 0.8 bar (11.6 psi) 0.51 I (1 .1 US pt) Regular brand-name gasoline (leaded or unleaded) and STIHL two-stroke engine oil min. 90 RON 50:1 with STIHL 50:1 two-stroke engine oil; 25:1 with other branded two-stroke, air-cooled engine oils Foam element Electronic (breakerless) magneto ignition 0.1-0.5 mm (0.004-0.020 in) 1.3-1.9 mm (0.05-0.07 in) B.T.D.C. at 6,000 rpm GM AC CSR 45 or NGK BMR 6 A 0.7-0.8 mm (0.027-0.030 in) M14x1.25 9.5 mm (0.37 in) 200 1.2 Fuel System 1.3 Ignition System

STIHL FS 36, 40, 44 5 FS 44 Spiral-toothed bevel gears 1.33 Deep groove ball bearings STIHL gear lubricant 0781 120 1117 6.1 kg 13.4 lb Full harness STIHL multi-purpose grease (80 g tube) 0781 120 1109 STIHL gear lubricant (80 g tube) 0781 120 1117 Safety goggles Transport guard for steel cutting tools 4130 007 1060 4130 007 1050 0457 281 3803 FS 40 5.3 kg 11.7 lb STIHL multi- purpose grease (80 g tube) 0781 120 1109 Safety goggles 4130 007 1060 4130 007 1050 0457 281 3803 FS 36 4.9 kg 10.8 lb 1.6 Special Accessories 1.6.1 For User 1.6.2 For Service Shop STIHL multi- purpose grease (80 g tube) 0781 120 1109 Safety goggles Carburetor parts kit Gasket kit Gasket panel 4130 007 1060 4130 007 1050 0457 281 3803 1.4 Gearhead Type: Gear ratio: Bearings: Lubrication: 1.5 Weights without cutting tool and deflector

STIHL FS 36, 40, 44 6 1.7 Tightening Torques (Ibf.ft) (1.8) (12.5) (2.2) (1 .5) (1 .8) (1 .8) (2.6) (2.6) (4.0) (4.0) (2.6) (2.6) For component Clutch drum to crankshaft Clutch to crankshaft Fixing screw on deflector Support plate, diaphragm, diaphragm carrier Control handle Loop handle Cap on clutch housing (FS 40, 44) Clutch housing to fan housing Fan housing to spiral housing Diaphragm carrier to crankcase Shroud to fan housing Shroud, carburetor, diaphragm carrier However, it is essential to always use a torque wrench to tighten the screw to the specified torques. If pneumatic or electric screwdrivers are used to fit DG screws in polymer components, always select a tightening torque below the value given in the table. Then use a torque wrench to check the tightening torque and correct it as necessary. Thread size IS 8-32* 3/8" 24* B3.5x9.5 B3.9x19 IS-DG5x16 IS-DG5x16 IS-DG5x16 IS-DG5x16 IS-DG5x16 IS-DG5x24 IS-DG5x60 Fastener Spline screw (captive) Clutch Self-tapping screw Self-tapping screw Spline screw Spline screw Spline screw Spline screw Spline screw Spline screw Spline screw Torque Nm 2.5 17.0 3.0 2.0 2.5 2.5 3.5 3.5 5.5 5.5 3.5 3.5 Remarks The new "DG" screws are used in the light-alloy and fiberglass reinforced polymer components of models FS 36, 40 and 44. When screwed in for the first time, DG screws form a permanent thread in the parts concerned. They can be released and retightened as often as necessary without affecting the strength of the screwed assembly.

STIHL FS 36, 40, 44 7 Fastener Spline screw Spline screw Spline screw Spline screw Spline screw Spline screw Spline screw Spline screw Spark plug Special screw " inch thread Thread size IS-DG5x60 IS-M4x20 IS-M5x18 IS-M5x18 IS-M5x20 IS-DG6x18 IS-M6x12 M6x50 M14x1.25 P5x14 For component Muffler to cylinder Ignition module to cylinder Clamp on clutch housing Clamp on bearing housing Clamp screw on gearhead (FS 44) Cylinder to crankcase Spiral housing to crankcase Clamp screw in loop handle Spark plug Filter cover to shroud Remarks Torque Nm 6.5 3.5 6.5 6.5 5.5 14.0 14.0 3.5 19.0 2.5 (Ibf.ft) (4.8) (2.6) (4.8) (4.8) (4.0) (10.3) (10.3) (2.6) (14.0) (1 .8)

STIHL FS 36, 40, 44 8 2. TROUBLESHOOTING CHARTS 2.1 Clutch Condition Insufficient frictional contact - clutch slips Cutting tool rotates while engine is idling 2.2 Engine Condition Engine does not start easily, stalls at idle speed, but operates normally at full throttle Engine does not deliver full power or runs erratically Engine overheating Cause Clutch springs stretched or fatigued, spring hooks broken Engine idle speed too high Clutch springs stretched or fatigued, spring hooks broken Cause Oil seal in crankcase leaking Gaskets on diaphragm carrier leaking Diaphragm faulty Cylinder base gasket leaking Crankcase damaged (cracks) Diaphragm carrier damaged (cracks) Secondary air seepage through faulty gaskets on diaphragm carrier Piston ring leaking or broken Muffler carbonized Insufficient cylinder cooling. Cooling fins very dirty Remedy Fit new springs Correct at idle speed adjusting screw Fit new springs Remedy Replace oil seal Replace gaskets Replace diaphragm Replace gasket Replace crankcase Replace diaphragm carrier Replace gaskets Fit new piston ring Clean muffler (inlet and exhaust), replace spark arrestor screen Thoroughly clean cylinder fins

STIHL FS 36, 40, 44 9 2.3 Ignition System Warning: 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! Ignition system in order. Look for fault in fuel system and carburetor. yes Replace ignition module. Does engine now run after positive spark test? Fit new flywheel. Does spark test now produce sparkover? Does flywheel appear to be in good condition? Fit new spark plug. Is air gap correct? Adjust air gap (0.1 - 0.5 mm). Is spark test positive? Insert screwdriver in place of spark plug in spark plug terminal and hold about 4 mm (1/8") away from ground. Sparkover? Replace faulty ignition lead of short circuit wire. Repair contact spring. Faulty insulation on ignition lead or short circuit wire? Clean spark plug and reset electrode gap. Does spark test produce powerful spark? Press terminal firmly onto spark plug and fit spring if necessary. Spark plug terminal firmly seated on spark plug? Remove spark plug. Is it in good condition? no no no no yes no no yes yes no no no no yes yes

STIHL FS 36, 40, 44 10 Condition Starter rope broken Rewind spring broken Starter rope can be pulled out almost without resistance (crankshaft does not turn) Starter rope is difficult to pull and rewinds very slowly Cause Rope pulled out too vigorously as far as stop or over edge Spring overtensioned - no reserve when rope is fully extended Pawl arm is worn Pawl spring fatigued or broken Starter mechanism is very dirty Lubricating oil on rewind spring becomes viscous at very low outside tempera- tures (spring windings stick together) Remedy Fit new starter rope Fit new rewind spring Fit new pawl Fit pawl spring Thoroughly clean complete starter mechanism Apply a few drops of kerosine (paraffin) to spring, then pull rope carefully several times until normal action is restored 2.4 Rewind Starter

Stihl FS 36, FS 40, FS 44 Brushcutters Full Service & Repair Manual

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