The Husqvarna 51 is a professional-grade chainsaw designed for demanding forestry and arborist work. This service manual provides comprehensive information for maintenance, troubleshooting, and repair. It covers the 51cc engine, automatic oiler, chain brake system, air filtration, ignition, carburetion, fuel system, and all critical safety components. Below are key sections for safety, specifications, maintenance procedures, troubleshooting, and parts identification.
Key components: 51cc X-Torq engine, Inertia-activated chain brake, Combined choke/stop control, Side-mounted chain tensioner, Automatic chain oiler with adjustable flow, Anti-vibration system, Quick-release air filter.
| Feature | Description |
|---|---|
| Engine Type | 2-stroke, single cylinder, air-cooled |
| Displacement | 51 cc (3.1 cu in) |
| Power Output | 3.1 hp (2.3 kW) |
| Fuel Tank Volume | 0.55 US qt (0.52 l) |
| Oil Tank Volume | 0.26 US qt (0.25 l) |
| Recommended Bar Length | 13" to 20" (33 cm to 50 cm) |
| Chain Pitch | 0.325" or 3/8" |
| Chain Gauge | 0.058" (1.5 mm) or 0.063" (1.6 mm) |
| Ignition System | Electronic, SEM or equivalent |
| Weight (powerhead) | 11.7 lbs (5.3 kg) |
Always wear appropriate PPE: helmet, eye protection, hearing protection, gloves, chainsaw chaps, and steel-toed boots.
WARNING! Failure to follow safety instructions can result in serious injury or death. The chain brake is a safety device; test it before each use.
Daily or before each use: Check chain tension, sharpness, and lubrication. Check throttle trigger, lockout, and stop switch function. Clean air filter. Check for loose nuts/bolts.
Weekly or every 10 hours: Clean cooling fins and cylinder cover. Clean spark arrestor screen (if equipped). Check fuel filter. Clean exterior of carburetor.
Monthly or every 20 hours: Replace spark plug. Clean fuel tank filter cap. Check/replace fuel line. Inspect clutch, drum, and sprocket.
Annually or every 100 hours: Clean combustion chamber. Check piston and cylinder for scoring. Replace impulse line. Overhaul carburetor if necessary.
Top End (Cylinder & Piston): Remove muffler to inspect piston through exhaust port. Scoring indicates air filter failure or lean mixture. Use ring compressor for piston installation. Torque cylinder nuts to 10 Nm (7.4 ft-lb).
Crankcase & Bearings: Check crankshaft play. Main bearings should rotate smoothly without noise. Seal replacement requires case splitting.
Clutch & Sprocket: Clutch springs should be intact. Centrifugal clutch engages at ~2,700 RPM. Replace spur or rim sprocket when worn.
Ignition Coil Air Gap: Set to 0.3 mm (0.012") between flywheel and coil legs.
Chain Tension: Correct when snug against bar but can be pulled around by hand. Adjust via side tensioner when cold.
Sharpening: Use round file matching chain pitch (typically 5/32" for 0.325" chain). Maintain 30° cutting angle and 10° top plate angle. File all cutters to equal length.
Bar Care: Clean bar groove weekly. Flip bar monthly for even wear. Dress rails with flat file if burred.
Tip: Always match chain pitch and gauge to bar and sprocket. A loose chain increases wear and risk of derailment.
Fuel System: Tank vent must be clear. Fuel line (ID 3.5mm) and filter should be replaced annually. Primer bulb (if equipped) should fill without air bubbles.
Automatic Oiler: Flow adjusted via screw on bottom of saw. Test by running at full throttle on a piece of cardboard; should throw a fine line of oil. Check oil pump diaphragm and plunger for wear.
Manual Oiler (if equipped): Activate by pressing plunger on front handle.
Oil Passage: Ensure bar mount holes and tank outlet are clear of debris.
WARNING! Use only biodegradable chain oil or equivalent. Never use waste oil, which damages pump and environment.
Factory settings (Zama C1Q): L: 1 turn out, H: 1 turn out, T: 1 turn out. Final adjustment requires tachometer.
CAUTION! Over-leaning (turning screws in too far) causes engine damage. Rich running is safer than lean.
Spark Plug: Replace annually. Gap to 0.5 mm (0.020"). Check for wet (flooding) or black sooty (rich) deposits.
Ignition Module: Test with spark tester. Minimum spark gap should be 6 mm (1/4") with strong blue spark. Check stop switch wire for continuity to ground when pressed.
Flywheel: Key must align with crankshaft slot. Torque nut to 40 Nm (29.5 ft-lb). Check magnets for cracks.
Wiring: Inspect for chafing, especially near handle and clutch cover.
| Symptom | Possible Cause | Corrective Action |
|---|---|---|
| Engine won't start | No spark, flooded, fuel issue | Check spark, plug condition. Dry plug, use choke correctly. Check fuel line, filter, carburetor diaphragm. |
| Engine starts then dies | Clogged fuel filter, tank vent, carb settings | Replace fuel filter. Clean tank vent. Check carburetor L and H settings. |
| Lacks power under load | Dirty air filter, clogged spark screen, carb adjustment | Clean/replace air filter. Clean muffler spark arrestor. Adjust H screw (richer). |
| Chain does not oil | Empty oil tank, clogged passages, faulty pump | Fill tank. Clean bar groove and oil holes. Check oil pump diaphragm and drive gear. |
| Excessive vibration | Unbalanced chain, loose components, engine mount | Sharpen chain evenly. Tighten all bolts. Check anti-vibration mounts for wear. |
| Chain rotates at idle | Idle speed too high, clutch springs | Adjust idle screw (T) counterclockwise. Inspect clutch springs for wear/breakage. |
Reset: For electronic ignition, disconnect spark plug wire to reset module if overheated.
Service: For genuine Husqvarna parts and technical support, contact an authorized Husqvarna service dealer.
Refer to official Husqvarna parts catalog for exploded views and part numbers for: Cylinder Group, Crankcase Group, Fuel Tank Group, Handle Group, Clutch & Sprocket Group, Chain Brake Group, and Bar & Chain Group.
Common Part Numbers (Example):
Air Filter: 503 87 47-01
Spark Plug: 503 87 64-01
Fuel Filter: 501 87 56-01
Oil Pump: 501 87 65-01
Clutch Drum: 501 87 71-01
Note: Part numbers may vary by serial number and production year. Always verify with your specific model.