The Stihl HT 131 is a professional-grade pole pruner designed for demanding arborist work. This service manual provides comprehensive information for maintenance, troubleshooting, and repair of the HT 131 powerhead. It covers safety procedures, technical specifications, engine components, fuel system, ignition system, cutting attachment, and step-by-step repair instructions. Below are key sections for safe operation, maintenance intervals, component specifications, disassembly procedures, and troubleshooting guides.
Essential safety precautions for servicing the Stihl HT 131. Failure to follow these instructions can result in serious injury or damage to the unit.
| Hazard | Precaution |
|---|---|
| Fuel Fire/Explosion | Work in well-ventilated area away from sparks or open flames. Drain fuel tank before any service. |
| Hot Surfaces | Allow engine to cool completely before disassembly. Cylinder and muffler can cause severe burns. |
| Sharp Cutters | Always wear cut-resistant gloves when handling the saw chain or guide bar. |
| Spring Force | The starter recoil spring is under tension. Use proper tools and follow procedure for safe removal. |
| Electrical Shock | Disconnect the spark plug boot and secure it away from the plug before beginning any work. |
Technical data and main components of the Stihl HT 131 powerhead.
Recommended service intervals to ensure optimal performance and longevity.
WARNING! Use only genuine STIHL replacement parts to maintain safety and performance certifications.
Service procedures for the fuel tank, lines, filter, and Zama carburetor.
Fuel Line Replacement:
Carburetor Adjustment (Standard Settings): L screw: 1 turn open. H screw: 1 turn open. LA (idle speed): Set to achieve 2,800 RPM idle. Final adjustment must be made with engine at operating temperature and using a tachometer.
Testing and replacement of ignition coil, spark plug, and stop switch.
| Component | Test Procedure | Specification |
|---|---|---|
| Spark Plug | Visual inspection for cracks, electrode erosion. Check gap. | BR7ES (NGK), Gap: 0.5 mm (0.020 in.) |
| Ignition Coil | Measure primary and secondary resistance with multimeter. | Primary: ~0.5-1.5 Ω, Secondary: ~8-15 kΩ (values may vary, consult specific chart). |
| Stop Switch | Continuity test. Circuit should be open when switch is OFF, closed when ON. | N/A |
Note: A failing ignition coil may cause weak spark, hard starting, or high RPM misfire.
Diagnosing engine performance issues, compression testing, and cylinder/piston inspection.
CAUTION! Scoring deeper than 0.1 mm typically requires cylinder replacement or professional replating.
Service for the pole pruner attachment, drive shaft, gearhead, and chain lubrication system.
Gearhead Greasing: Remove cover plate and pack with STIHL Polyrex grease. Check gear teeth for wear or pitting.
Drive Shaft Inspection: Remove from pole. Check for straightness and that the hex end is not rounded. Lubricate shaft lightly before reinsertion.
Oil Pump Flow Test: Run engine at wide open throttle with bar tip near a clean surface. A steady line of oil should be thrown from the chain within 30 seconds. Adjust oiler screw if flow is insufficient.
Step-by-step guide for major component removal.
WARNING! Mark all components and their orientation. Take photos during disassembly for reference.
Critical fastener torque values (in Newton meters, N·m). Use a calibrated torque wrench.
| Fastener | Torque (N·m) | Torque (in-lbs) |
|---|---|---|
| Cylinder Base Nuts | 20 N·m | 177 in-lbs |
| Spark Plug | 25 N·m | 221 in-lbs |
| Clutch Nut | 40 N·m (Left-hand thread) | 354 in-lbs |
| Flywheel Nut | 50 N·m | 443 in-lbs |
| Muffler Bolts | 10 N·m | 89 in-lbs |
| Gearhead Cover Bolts | 8 N·m | 71 in-lbs |
Diagnostic guides for common operational problems.
| Symptom | Possible Cause | Corrective Action |
|---|---|---|
| Engine will not start | 1. No spark 2. No fuel 3. Flooded | 1. Check plug, wire, coil, stop switch. 2. Check fuel line, filter, carburetor inlet. 3. Hold throttle wide open while cranking. |
| Engine starts but dies | 1. Clogged fuel filter/tank vent 2. Faulty carburetor diaphragms 3. Air leak | 1. Replace filter, clear tank vent. 2. Rebuild carburetor kit. 3. Pressure test crankcase. |
| Loss of power at cut | 1. Dull chain 2. Clogged air filter 3. Fouled spark plug 4. Exhaust port carbon | 1. Sharpen chain. 2. Clean/replace filter. 3. Clean/replace plug. 4. Decarbonize. |
| Excessive vibration | 1. Unbalanced cutting attachment 2. Bent drive shaft 3. Worn antivibration mounts | 1. Check chain tension and balance. 2. Inspect and replace shaft. 3. Replace rubber mounts. |
| Chain does not oil | 1. Empty oil tank 2. Clogged oil passages 3. Faulty oil pump | 1. Fill tank. 2. Clean bar groove and oil holes. 3. Test and replace pump. |
Reference diagrams for ordering correct replacement parts. Diagrams include: Group 1110: Crankcase, Crankshaft, Bearings, Seals. Group 1120: Piston, Cylinder, Rings. Group 1130: Fan Housing, Recoil Starter. Group 1140: Carburetor, Air Filter, Fuel Tank. Group 1150: Ignition System, Switches. Group 1160: Clutch, Sprocket, Gearhead. Group 1170: Pole Pruner Attachment, Guide Bar, Saw Chain.
Parts Ordering: Always use the 10-digit STIHL part number from the corresponding exploded view. Provide model number (HT 131) and serial number when ordering.
Service Support: For technical assistance, contact an authorized STIHL servicing dealer. Manual No. 0000-970-8501.