Stihl 026 Power Tool Service Manual

STIHL 024, 026 2004-08 STIH)

1. Safety Precautions 1 2. Introduction 2 3. Specifications 3 3.1 Engine 3 3.2 Fuel System 3 3.3 Ignition System 4 3.4 Cutting Attachment 4 3.5 Special Accessories 4 3.5.1 For User 4 3.5.2 For Service 5 3.6 Tightening Torques 5 4. Clutch, Chain Drive, Chain Brake and Chain Tensioner 7 4.1 Clutch Drum and Chain Sprocket 7 4.2 Clutch 8 4.3 Chain Brake 9 4.3.1 Checking Function 9 4.3.2 Disassembling 9 4.3.3 Assembling 11 4.3.4 Anchor Pin for Brake Spring 13 4.3.5 Pin for Hand Guard 13 4.4 Front Chain Tensioner (024) 14 4.5 Side Chain Tensioner 14 5. Engine 15 5.1 Muffler/Spark Arresting Screen 15 5.2 Catalytic Converter 16 5.2.1 Construction and Function 16 5.3 Leakage Test 17 5.3.1 Preparations 17 5.3.2 Pressure Test 18 5.3.3 Vacuum Test 18 5.4 Oil Seals 19 5.5 Exposing the Cylinder 21 5.6 Cylinder and Piston 21 5.6.1 Removing 21 5.6.2 Installing 22 5.7 Piston Rings 25 5.8 Crankcase 25 5.8.1 Removing the Crankshaft 25 5.8.2 Installing the Crankshaft 28 5.9 Decompression Valve 33 6. Ignition System 33 6.1 Spark Plug Boot/ Ignition Lead 33 6.2 Ignition Module 34 6.2.1 Ignition Timing 35 6.2.2 Removing and Installing 35 6.3 Short Circuit Wire/ Ground Wire 36 6.4 Wiring Harness 37 6.5 Contact Spring 38 6.6 Flywheel 38 7. Rewind Starter 39 7.1 General 39 7.2 Rewind Spring 39 7.2.1 Replacing 39 7.2.2 Tensioning 40 7.3 Starter Rope/Starter Grip (ElastoStart) 41 8. AV Handle System 42 9. Master Control/ Handle System 43 9.1 Switch Shaft 43 9.2 Interlock Lever/ Throttle Trigger 43 10. Electric Handle Heating System 45 10.1 Troubleshooting 45 10.1.1 Troubleshooting Chart 46 10.1.2 Test Connections and Test Values 47 10.2 Heater Switch 48 10.3 Heating Element in Rear Handle 48 10.4 Heating Element in Front Handle 49 10.5 Generator 50 11. Chain Lubrication 52 11.1 Pickup Body/ Suction Hose 52 11.2 Valve 53 11.3 Oil Pump 53 11.3.1 Servicing 55 12. Fuel System 55 12.1 Air Filter/Choke Shutter 55 12.2 Carburetor Preheating 56 12.3 Carburetor Heater 56 12.3.1 Construction and Function 56 12.3.2 Testing 57 12.3.3 Troubleshooting Chart 59 12.4 Printed Circuit Board 60 12.5 Carburetor 60 12.5.1 Leakage Testing 60 12.5.2 Removing and Installing 61 12.5.3 Adjusting 63 12.6 Tank Vent 64 12.7 Fuel Hose 65 12.8 Tank Housing 65 13. Special Servicing Tools and Aids 68 13.1 Special Servicing Tools 68 13.2 Servicing Aids 70 1. 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 war- nings in the owner’s manual. Gasoline is an extremely flamm- able fuel and can be explosive in certain conditions. Improper handling may result in burns or other serious injuries. Warning! Do not smoke or bring any fire or flame near the fuel. All work with fuel must be performed outdoors only. Spilled fuel must be wiped up immediately. Wash hands thoroughly after every contact with waste oil. Do not pour waste oil down the drain or allow it to soak into the ground. Collect waste oil and take it to an official disposal site for environ- ment-friendly disposal. © 1999 Andreas Stihl AG & Co., Waiblingen CONTENTS 024, 026 1

This service manual contains detailed descriptions of all the repair and servicing procedures specific to this power tool series. There are separate handbooks for servicing procedures for standardized parts and assemblies that are installed in several STIHL power tool models. Reference is made to these handbooks in the appropriate chapters of this manual. As the design concept of model 024 and 026 chainsaws is almost identical, the descriptions and servicing procedures generally apply to both. Differences are described in detail. Servicing procedures on the carburetor are described in the "Carburetors" handbook. 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 needed. Parts lists on microfiche and CD- ROM are always more up to date than printed lists. A fault on the machine may have several causes. To help locate the fault, consult the troubleshooting charts for all assemblies in the "Standard Repairs, Troubleshoot- ing" handbook. Refer to the "Technical Informa- tion" bulletins for engineering changes which have been intro- duced since publication of this service manual. Technical information bulletins also supplement the parts list until a revised edition is issued. The special servicing tools mentioned in the descriptions are listed in the last chapter of 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: = Pointer = Direction of movement Service manuals and all technical information bulletins describing engineering changes are intended exclusively for the use of STIHL servicing dealers. They must not be passed to third parties. Servicing and repairs are made considerably easier if the machine is mounted on assembly stand (1) 5910 890 3100. Remove the chain sprocket cover and secure the machine to the assembly stand with the sprocket cover nuts. Machines with a quick chain tensioning system and secure with one M8 nut and washer. The complete unit can then be swivelled to the best position for the ongoing repair. This leaves both hands free. Always use original STIHL replacement parts. They can be identified by the STIHL part number, the logo and the STIHL parts symbol The symbol may appear alone on small parts. 2. INTRODUCTION VA 133RA001 1 2 024, 026

3.1 Engine STIHL single-cylinder two-stroke engine with special impregnated cylinder bore 024 024 S 026 Displacement: 42 cm 3 (2.56 cu.in) 44.3 cm 3 (2.70 cu.in) 48.7 cm 3 (2.97 cu.in) Bore: 42 mm (1.65 in) 42 mm (1.65 in) 44 mm (1.73 in) Stroke: 30 mm (1.18 in) 32 mm (1.26 in) 32 mm (1.26 in) Engine power to ISO 7293: 2.1 kW (2.85 bhp) 2.3 kW (3.1 bhp) 2.6 kW (3.5 bhp) at 7,000 rpm at 7,000 rpm at 7,000 rpm Max. permissible engine speed with bar and chain: 13,000 rpm 13,000 rpm 14,000 rpm Idle speed: 2,500 rpm Bearings: Crankshaft supported in heavy-duty deep-groove ball bearings, needle cages on small and big ends Piston pin diameter: 10 mm (0.39 in) Rewind starter: Single pawl system Reserve pull on rope rotor: min. 1/2 turn Starter rope: 3.5 mm (0.14 in) dia. Clutch: Centrifugal clutch without linings Clutch engages at: 3,600 rpm Crankcase leakage test at gauge pressure: 0.5 bar (7.25 psi) under vacuum: 0.5 bar (7.25 psi) 3.2 Fuel System Carburetor: Diaphragm carburetor Setting High speed screw H: approx. 1 turn open Low speed screw L: approx. 1 turn open (standard setting) Carburetor leakage test at gauge pressure: 0.8 bar (11.6 psi) Function of tank vent at gauge pressure: ≤ 0.3 bar (4.35 psi) under vacuum: * ≤ 0.05 bar (0.725 psi) Fuel tank capacity: 0.47 L (16 fl.oz) Octane number: min. 90 RON Fuel mixture: Regular brand-name gasoline and two-stroke engine oil Mix ratio: 50:1 with STIHL 50:1 two-stroke engine oil 25:1 with other brand-name two-stroke, air-cooled engine oils Air filter: Large area, bisectional flat filter, additional prefilter in carburetor box cover * Original tank vent 3. SPECIFICATIONS 024, 026 3

3.3 Ignition System Type: Electronic magneto ignition (breakerless) with integral trigger unit Air gap: 0.2-0.3 mm (0.008-0.012 in) Spark plug (suppressed): Bosch WSR 6F, NGK BPMR 7 A or Champion RCJ 6Y Electrode gap: 0.5 mm (0.020 in) 3.4 Cutting Attachment Guide bars: STIHL Rollomatic with nose sprocket, corrosion-resistant finish and induction hardened rails Bar lengths: 32, 37 and 40 cm (13, 15, 18 in) Oilomatic chain: 0.325" (8.25 mm) Rapid chain Chain sprocket: 7-tooth 0.325" Chain speed: 18.3 m/s (60 ft/s) at 9,500 rpm Chain lubrication: Speed-controlled or adjustable reciprocating pump Oil feed rate on non-adjustable pump: 6 cm 3 /min (0.2 fl.oz/min) at 6,000 rpm 9.5 cm 3 /min (0.3 fl.oz/min) at 10,000 rpm on adjustable pump: 4.5-11.5 cm 3 /min (0.15-0.4 fl.oz/min) at 10,000 rpm Oil tank capacity: 0.32 L (11 fl.oz) 3.5 Special Accessories 3.5.1 For User ElastoStart 0000 190 3401 Air filter, "fleece" 024 1121 120 1625 0.325", 8-tooth chain sprocket 1121 640 2001 1) 1121 640 2005 2) Intake air preheating kit 024 1121 007 1030 Intake air preheating kit 026 1121 007 1027 (up to serial number X 30 976 774) Intake air preheating kit 026 1121 007 1044 (from serial number X 30 976 775) 0.325", 7-tooth rim sprocket kit 1121 007 1001 1) 1121 007 1037 2) 0.325", 8-tooth rim sprocket kit 1121 007 1002 1) 1121 007 1038 2) 3/8" Picco, 7-tooth rim sprocket kit 1121 007 1004 1) 1121 007 1039 2) 3/8" Picco, 8-tooth rim sprocket kit 1121 007 1005 1) 1121 007 1040 2) 3/8", 7-tooth rim sprocket kit 1121 007 1035 1) 1121 007 1041 2) Chain scabbard extension (from 45 cm/18 in) 0000 792 9131 CAT mounting kit 1121 007 1042 1) 024 2) 026 4 024, 026

3.5.2 For Service Carburetor parts kit 024, small 1118 007 1060 (Tillotson) Carburetor parts kit 024, large 1118 007 1065 (Tillotson) Carburetor parts kit 024/026, large 1121 007 1062 (Walbro) Carburetor parts kit 024/026, large 1118 007 1066 (Walbro WT 22) Gasket set 024/026 1121 007 1050 3.6 Tightening Torques Plastoform screws are used for polymer 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 detrimentally affecting 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 For component Torque Remarks size Nm lbf.ft Pan head screw M4x8 Cover plate/chain tensioner 3.0 2.2 Countersunk screw PT4x12 Cover plate/chain sprocket cover 2.5 1.8 1) Collar screw M8x21.5 Bar mounting 23.0 17.0 2) Collar screw M10/M8 Bar mounting 30.0 22.0 1) 3) Spline screw IS-M4x12 Cover to crankcase, sprocket side 3.0 2.2 M10x1 Decompression valve 14.0 10.3 4) Self-tapping screw B4.2x9.5 Spark arresting screen 2.0 1.5 Spline screw M3.5x12 Generator 2.0 1.5 2) Self-tapping screw IS-P6x19 Front handle top/bottom (W version) 7.0 5.2 Self-tapping screw IS-P6x32.5 Front handle, top (polymer) 5.0 3.7 Self-tapping screw IS-P6x21.5 Front handle, bottom (polymer) 5.0 3.7 Self-tapping screw B3.9x19 Handle molding 1.6 1.2 Screw assembly IS-M4x16 Hand guard, left 4.0 3.0 Slotted nut M5 Shroud to cylinder 3.5 2.6 Self-tapping screw IS-P6x19 Chain catcher/plug 2.8 2.1 Spline screw IS-M5x12 Spiked bumper (with self-locking nut) 7.5 5.5 Spline screw IS-M5x20 Crankcase 9.0 6.6 Mutter M5 Air filter 2.0 1.5 Spline screw IS-M4x16 Fan housing 4.0 3.0 M12x1L Clutch carrier 50.0 37.0 Self-tapping screw IS-P6x26.5 Annular buffer to tank housing, left 5.0 3.7 Self-tapping screw IS-P6x19 Annular buffer to tank housing, right 5.0 3.7 024, 026 5

Fastener Thread For component Torque Remarks size Nm lbf.ft Spline screw IS-M5x12 Annular buffer plate 8.0 5.9 2) Spline screw IS-M5x16 Muffler to crankcase (Cat version) 10.0 7.5 2) Spline screw IS-M5x12 Muffler to crankcase (non-Cat version) 10.0 7.5 2) Spline screw IS-M5x12 Muffler to cylinder 10.0 7.5 2) Spline screw IS-M5x12 Upper casing to muffler (non-Cat version) 10.0 7.5 Spline screw IS-M5x16 Upper casing to muffler (Cat version) 10.0 7.5 Nut M8x1 Flywheel 33.0 24.4 Spline screw M4x8 Side plate 3.0 2.2 Self-tapping screw BM4x16 Side plate 3.0 2.2 1) Stud M5x8.5 Stud to cylinder, left 1.4 1.1 3) Stud M5x8.5 Stud to cylinder, right 1.4 1.1 Nut M5 Carburetor 3.5 2.6 Spline screw IS-M5x20 Cylinder 10.5 7.7 M14x1.25 Spark plug 25.0 18.5 Spline screw IS-M5x20 Ignition module 7.0 5.2 2) 5) Spline screw IS-M4x12 Oil pump 3.5 2.6 Use the following procedure when refitting a P screw in an existing thread: – Place the P 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, i.e. the thread is not weakened. 1) On machines with quick chain tensioner 2) Secure screw with Loctite 242. 3) Secure screw with Loctite 270. 4) On 026 only 5) A washer must be fitted under the screw head. Note: Screws secured with adhesive (Loctite) are easier to release if they are heated with a hot air blower (hair dryer). Take care on polymer components. Power screwdriver setting for use in polymer: max. 600 rpm for Plastoform screws 6 024, 026

- Remove the chain sprocket cover. • Disengage the chain brake by pulling the hand guard toward the front handle. • Remove the E-clip (1). • Remove the washer (2). - If a rim sprocket is fitted, pull it off. • Pull off the clutch drum/chain sprocket. • Remove the needle cage. - Clean and inspect the clutch drum/chain sprocket. Important: If there are noticeable wear marks on the inside diameter of the clutch drum, check its wall thickness. If it is less than 80% of the original wall thickness, fit a new clutch drum. Note: If the clutch drum has to be replaced, also check the brake band - see 4.3.2. • If the clutch drum is still service- able, use No. 120 emery paper or emery cloth (grain size approx. 120µm) to clean and roughen its friction surface. Reassemble in the reverse sequence. - Clean stub of crankshaft. Wash needle cage in clean white spirit and lubricate with grease - see 13.2. - Replace damaged needle cage. - On 026, rotate clutch drum/chain sprocket and apply slight pressure at the same time until driver on oil pump worm engages the notch on the drum’s circumference. - If machine is equipped with a rim sprocket, refit it so that the cavities face outwards. 4. CLUTCH, CHAIN DRIVE, CHAIN BRAKE AND CHAIN TENSIONER 4.1 Clutch Drum and Chain Sprocket VA 143RA007 VA 170RA005 VA 133RA002 1 2 80% 100% 145RA006 ! VA VA 133RA003 024, 026 7

Troubleshooting chart - see "Standard Repairs, Trouble- shooting" handbook. - Remove the clutch drum/chain sprocket - see 4.1. - Remove the air filter - see 12.1. • Unscrew slotted nut from the shroud. - Remove the shroud. - Pull off the spark plug boot. - Unscrew the spark plug. • Close the decompression valve (1), where fitted. • Push the locking strip (2) 0000 893 5903 into the cylinder. • Unscrew the clutch in the direction of the arrow (left-hand thread). - Disassemble and reassemble the clutch - see "Standard Repairs, Troubleshooting" handbook. • On 024, if a cover washer is fitted behind the original clutch, do not refit it when installing the new clutch. • Screw clutch onto crankshaft and torque down to 50 Nm (37 lbf.ft). - Remove locking strip from cylinder. - Install spark plug and torque down to 25 Nm (18.5 lbf.ft). • On machines with a decompression valve, make sure the cover is properly seated. • If the shroud is replaced on a 026 machine without decompression valve, seal the opening in the shroud with the cap. • Check condition of heat shield (foil) and fit a new one if necessary. - Fit the shroud. 4.2 Clutch VA 133RA007 VA 133RA010 VA 133RA004 VA 133RA008 VA 133RA035 VA 133RA006 2 1 VA 133RA009 VA 133RA005 8 024, 026

The chain brake is one of the most important safety devices on the chain saw. Its efficiency is measu- red in terms of braking time, i.e. the time that elapses between activating the brake and the saw chain coming to a standstill. The shorter the braking time, the better the efficiency and protection offered. Contamination (with chain oil, chips, fine particles of abrasion, etc.) and smoothing of the friction surfaces of the brake band and clutch drum impair the coefficient of friction. This, in turn, reduces the frictional forces and thus pro- longs the braking time. A fatigued or stretched brake spring has the same negative effect. - Start the engine. - With the chain brake activated (locked), open throttle wide for brief period (max. 3 seconds) - the chain must not rotate. - With the chain brake released, open throttle wide and activate the brake manually - the chain must come to an abrupt stop. Note: The braking time is in order if deceleration of the saw chain is imperceptible to the eye. - Remove clutch drum/chain sprok- ket - see 4.1. - Relieve tension of brake spring by pushing hand guard forwards. • Take out the screw. - Remove the side plate. • On 026, remove the upper bumper strip from the chain tensioner. • Take out the screws. - Remove the cover. • Carefully pry the brake spring off the anchor pin and unhook it from the bell crank. • Lever the brake band out of the crankcase. - Unhook the brake band from the bell crank. 4.3 Chain Brake 4.3.1 Checking Function 4.3.2 Disassembling VA 133RA013 VA 133RA014 VA 133RA011 VA 133RA012 133RA015 VA 024, 026 9

Stihl 026 Power Tool Service Manual

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