STIHL Chainsaw 024 026 Service Repair Manual

This comprehensive service and repair manual covers the STIHL 024 and 026 chainsaw models. It provides detailed instructions for maintenance, troubleshooting, disassembly, repair, and reassembly of all major components including the engine, fuel system, ignition, chain brake, clutch, guide bar, and cutting chain. Intended for professional technicians and experienced users, it includes specifications, torque values, special tools, and exploded diagrams. Always prioritize safety: wear protective equipment, disconnect the spark plug before servicing, and work in a clean, well-ventilated area.

Safety Precautions & Symbols

Before any service, understand and follow all safety warnings to prevent fire, explosion, injury, or damage to the saw.

Symbol/Item	Meaning & Precaution
⚠️ General Warning	Indicates a potentially hazardous situation. Read accompanying instructions.
🔥 Fire Hazard	Fuel is highly flammable. No smoking. Work away from ignition sources.
⚡ Electrical Hazard	Disconnect spark plug boot before working on ignition or engine components.
🛠️ Sharp Edges	Wear cut-resistant gloves when handling chain, bar, or sharp components.
🧼 Clean Work Area	Keep area free of debris and fuel spills to prevent slips and fire.
👁️ Eye Protection	Always wear safety glasses or a face shield.
👂 Hearing Protection	Wear ear defenders during operation and certain repair procedures (e.g., testing).

Model Identification & Specifications

Identify your model via the serial number plate. Key specifications for the 024 and 026 series.

• Engine Type: Single cylinder, two-stroke, air-cooled.
• Displacement: 024: ~40.2 cc / 026: ~44.3 cc (confirm via serial).
• Fuel/Oil Mix: Use high-quality 2-stroke engine oil at 50:1 ratio (STIHL HP Ultra or equivalent).
• Ignition System: Electronic, breakerless.
• Carburetor: Walbro or Zama diaphragm type.
• Idle Speed: 2,800 - 3,200 RPM.
• Max Power Speed: ~13,000 RPM.
• Chain Pitch/Gauge: Typically .325" pitch, .063" gauge (confirm with bar marking).

WARNING! Using incorrect fuel mix or non-specified parts can cause severe engine damage and void warranty.

Special Tools & Workshop Requirements

Proper tools are essential for safe and correct repair.

1. STIHL Piston Stop Tool: For holding crankshaft when removing clutch/flywheel.
2. Clutch Removal Tool/Spanner: For securing clutch assembly during removal (right-hand thread).
3. Flywheel Puller: For removing flywheel without damage.
4. Compression Tester: To check engine health (expected: 120-150 psi).
5. Torque Wrench: In-lb and ft-lb ranges for precise fastener tightening.
6. Spark Tester/Gap Tool: Check spark and set electrode gap (0.020").
7. Workshop: Clean, organized bench with good lighting and ventilation.

Routine Maintenance Procedures

Regular maintenance prevents major failures and ensures optimal performance.

Task	Interval	Procedure
Air Filter Cleaning	Every 5-10 hours	Remove cover, tap out debris, wash in soapy water if foam, dry completely, lightly oil if specified.
Chain Sharpening & Tension	Before each use	File cutters to correct angle (30°), maintain depth gauges. Adjust tension so chain snaps back when pulled from bar groove.
Spark Plug Inspection	Every 25 hours	Remove, clean electrode, check gap (0.020"), replace if worn or fouled. Use correct heat range (BPMR7A).
Fuel Filter Replacement	Every season or 50 hours	Drain tank, use hook tool to extract filter from fuel line, replace with genuine STIHL part.
Bar Maintenance	Every chain sharpening	Clean bar groove, flip bar to ensure even wear, check for straightness and burrs.
External Cleaning	After each use	Use brush and damp cloth. Never use high-pressure water.

Fuel System Service

Problems often originate in the fuel system. Includes carburetor adjustment and repair.

1. Fuel Line & Filter: Inspect for cracks, stiffness, or leaks. Replace as a set if degraded.
2. Carburetor Diaphragms & Gaskets: Remove carb, disassemble, inspect pump and metering diaphragms for stiffness/holes. Replace kit if faulty.
3. Adjustment Screws (LA, H, L): Initial settings: Turn H and L screws gently clockwise to seat, then back out LA: 1 turn, H: 1 turn, L: 1 turn. Fine-tune for smooth idle and crisp acceleration.
4. Fuel Tank Vent: Check small vent in cap or tank. Clear blockage with compressed air.
5. Pressure/Vacuum Test: After reassembly, test carburetor with pressure/vacuum pump to check for leaks.

CAUTION! Use only ethanol-free fuel when possible to prevent carburetor damage. Always run saw dry for long-term storage.

Ignition System Service

Diagnosing no-spark conditions and coil replacement.

1. Safety First: Disconnect spark plug boot.
2. Spark Test: Insert spark tester between plug boot and plug. Pull starter. Look for bright blue spark.
3. No Spark Diagnosis: Check/clean spark plug. Inspect boot for cracks. Check stop switch wire for continuity to ground. Measure coil air gap (0.2-0.4mm) between flywheel magnets and coil legs.
4. Coil Replacement: Remove flywheel (requires puller). Note wiring routing. Install new coil, set gap with feeler gauge (a business card often works), torque mounting screws.
5. Flywheel Key: Inspect woodruff key for shearing. A sheared key causes timing issues and no spark.

Engine Disassembly & Reassembly

Major engine service including cylinder, piston, crankshaft, and bearings.

1. External Clean & Prep: Thoroughly clean saw exterior. Remove all external components: bar, chain, clutch, flywheel, fuel tank, carburetor, etc.
2. Split Crankcase: Remove all crankcase screws. Use a plastic mallet to gently tap case halves apart. Do not pry.
3. Piston & Cylinder Inspection: Look for scoring on piston skirts and cylinder walls. Light vertical marks are normal; deep horizontal scratches indicate failure. Measure piston ring end gap.
4. Crankshaft & Bearings: Check bearings for smooth rotation and no play. Replace if rough or noisy. Press crankshaft out of bearings using appropriate arbor press.
5. Reassembly: Use new gaskets and seals. Apply light oil to bearings and piston rings. Ensure crankshaft seals are properly seated. Torque crankcase screws in a criss-cross pattern to specification.

WARNING! Engine work requires precision. Label all parts and take photos during disassembly. Do not force components.

Clutch & Chain Brake Service

Servicing the centrifugal clutch and inertia-activated chain brake.

Component	Symptom	Service Action
Clutch Drum/Sprocket	Worn sprocket teeth, deep grooves in drum	Replace drum/sprocket assembly. Check bearing.
Clutch Shoes & Springs	Saw runs but chain doesn't turn; excessive wear on shoes	Replace clutch assembly. Springs must be intact.
Chain Brake Band	Brake does not stop chain; band is glazed or broken	Replace brake band. Clean all friction surfaces.
Brake Handle/Mechanism	Handle does not engage or return properly	Inspect for broken springs, bent linkages, debris. Lubricate pivot points.

Note: Clutch nut has a standard right-hand thread. Use piston stop to hold crankshaft while loosening.

Guide Bar & Chain Maintenance

Proper care extends bar and chain life and improves cutting performance.

1. Bar Groove Cleaning: Use a narrow bar groove cleaner or a stiff wire to remove packed sawdust and dirt.
2. Bar Rail Dressing: File down raised burrs on the bar rails with a flat file to prevent chain sticking.
3. Bar Flipping: Regularly flip the bar over to promote even wear on both sides.
4. Chain Sharpening: Use correct round file size (.325" chain uses a 4.0mm or 5/32" file). Maintain 30° cutter angle and 10° top plate angle. File all cutters to equal length.
5. Depth Gauge Setting: Use a depth gauge tool to file down rakers to proper height (typically 0.025" below cutter).
6. Lubrication: Ensure oiler port on bar is clear and oil tank is filled with proper bar & chain oil.

Troubleshooting Flowcharts

Systematic approach to common problems.

Symptom	Possible Cause	Corrective Action
Engine will not start	1. No fuel 2. No spark 3. Flooded 4. Compression low	1. Check fuel, filter, line. 2. Perform spark test. 3. Remove plug, dry cylinder, crank with throttle open. 4. Test compression; inspect piston/rings.
Engine starts but dies	1. Clogged fuel filter/vent 2. Faulty carburetor diaphragms 3. Air leak (crank seals, gaskets)	1. Replace filter, clear vent. 2. Rebuild carburetor. 3. Pressure test engine.
Lacks power under load	1. Clogged air filter 2. Exhaust port/muffler screen clogged 3. Incorrect carb adjustment 4. Worn piston/cylinder	1. Clean/replace filter. 2. Clean muffler/spark arrestor screen. 3. Adjust H and L screws. 4. Inspect top end.
Chain does not turn	1. Clutch worn 2. Sprocket worn 3. Chain brake engaged 4. Chain too tight	1. Replace clutch. 2. Replace drum/sprocket. 3. Disengage brake. 4. Loosen tension.
Excessive vibration	1. Unbalanced cutting chain 2. Loose engine mounts 3. Damaged crankshaft or clutch	1. Sharpen chain evenly. 2. Tighten all mounting bolts. 3. Inspect for damage, replace parts.

Torque Specifications & Diagrams

Critical fastener torque values. Do not over-tighten.

• Cylinder Head Nuts: 180-200 in-lb (15-16.7 ft-lb)
• Crankcase Screws: 70-80 in-lb (5.8-6.7 ft-lb)
• Clutch Nut: 250-300 in-lb (20.8-25 ft-lb) - RIGHT-HAND THREAD
• Flywheel Nut: 220-260 in-lb (18.3-21.7 ft-lb)
• Spark Plug: 150-180 in-lb (12.5-15 ft-lb)
• Guide Bar Nuts: 70-90 in-lb (5.8-7.5 ft-lb)

Exploded Diagrams: Refer to official STIHL parts diagrams (available online) for part numbers and assembly order. Always use genuine STIHL or high-quality OEM-equivalent replacement parts.

Final Note: After any major repair, start the saw and let it idle, then check for leaks, unusual noises, and proper chain operation before putting it under load.