The STIHL MS 440 is a professional-grade chainsaw featuring a high-performance engine, advanced anti-vibration system, and robust construction for demanding forestry and cutting applications. This repair manual provides comprehensive instructions for maintenance, troubleshooting, disassembly, and reassembly of key components including the engine, fuel system, ignition, chain brake, and cutting attachment. Below are essential sections covering safety, specifications, maintenance procedures, and step-by-step repair guides.
Always prioritize safety when performing repairs. Wear appropriate PPE including gloves, safety glasses, and hearing protection.
| Hazard | Precaution |
|---|---|
| Fuel & Oil Spills | Work in well-ventilated area; avoid open flames or sparks. |
| Sharp Components | Handle chain, bar, and cutting edges with cut-resistant gloves. |
| Hot Surfaces | Allow engine and muffler to cool completely before disassembly. |
| Spring-Loaded Parts | Use proper tools to contain tension (e.g., clutch spring). |
| Electrical Shock | Disconnect spark plug wire before working on ignition system. |
Standard and specialty tools needed for effective repair.
WARNING! Use genuine STIHL tools where specified to avoid damage.
Follow intervals based on operating hours or fuel consumption.
| Component | Interval | Action |
|---|---|---|
| Air Filter | Every 10 hours | Clean with compressed air; replace if damaged. |
| Spark Plug | Every 50 hours | Clean electrode; gap to 0.5mm; replace if worn. |
| Fuel Filter | Every 3 months | Replace in-tank filter; clean fuel line. |
| Chain & Bar | Daily | Check tension; lubricate groove; rotate bar. |
| Clutch Drum/Sprocket | Every 100 hours | Inspect wear; replace if sprocket teeth are hooked. |
| Anti-Vibration Buffers | Annually | Check for cracks or hardening; replace set. |
Cylinder, piston, crankshaft, and bearings service.
CAUTION! Label all parts during disassembly; use torque wrench for reassembly.
Carburetor, fuel lines, tank, and filter maintenance.
Tip: Always use fresh, mixed fuel (50:1 STIHL HP Ultra oil) to prevent varnish.
Spark plug, coil, flywheel, and switch testing.
| Symptom | Test | Solution |
|---|---|---|
| No spark | Check plug gap; test with known-good plug. | Replace spark plug; check kill switch continuity. |
| Intermittent spark | Inspect wire insulation; check coil air gap (0.3mm). | Adjust flywheel-to-coil gap; replace coil if cracked. |
| Weak spark | Measure coil primary resistance (≈1Ω) and secondary (≈5kΩ). | Replace ignition module if out of spec. |
| Flywheel key sheared | Inspect keyway; check timing alignment. | Replace key; torque flywheel nut to 40 Nm. |
Sharpening, tensioning, and wear inspection.
WARNING! Always stop engine and wear gloves when handling chain.
Removal, inspection, and replacement procedure.
CAUTION! Clutch springs are under tension; wear eye protection during removal.
Springs and rubber buffers replacement.
Four main AV points: front handle, rear handle, and engine mounts.
Tip: Excessive vibration can indicate failed AV buffers; replace promptly to reduce operator fatigue.
| Problem | Possible Cause | Corrective Action |
|---|---|---|
| Hard starting | Fouled spark plug, stale fuel, clogged carburetor. | Replace plug; drain fuel; clean carburetor jets. |
| Loss of power | Clogged air filter, exhaust screen carboned, low compression. | Clean filter; remove muffler screen; check piston/cylinder. |
| Chain oil not flowing | Clogged oiler holes, worn pump, incorrect oil viscosity. | Clean bar groove; replace oil pump; use STIHL chain oil. |
| Overheating | Lean carburetor setting, insufficient lubrication, dirty cooling fins. | Adjust H & L screws; check oil flow; clean cylinder fins. |
| Chain brake failure | Worn band, dirty mechanism, weak spring. | Inspect band thickness; clean pivot points; replace spring. |
Reset: After repairs, reset carburetor to factory settings and retune.
Service Support: For genuine parts and technical assistance, contact authorized STIHL dealers or visit www.stihlusa.com.