Stihl HT 131 Repair Manual

The Stihl HT 131 is a professional-grade pole pruner designed for demanding arborist and landscaping work. This manual provides comprehensive repair, maintenance, and troubleshooting information for the HT 131 powerhead, including its engine, fuel system, ignition, cutting attachment, and pole assembly. Below are key sections covering safety, specifications, disassembly, component repair, assembly, and troubleshooting procedures.

Safety Precautions

Before performing any repair, ensure the unit is off, cool, and the spark plug boot is disconnected. Wear appropriate PPE (safety glasses, gloves). Work in a clean, well-ventilated area. Use only genuine Stihl replacement parts.

Hazard	Precaution
Fuel Fire/Explosion	Drain fuel tank before disassembly. Keep away from sparks/open flames.
Sharp Components	Handle cutting attachment and drive shaft with care.
Spring Tension	Clutch and starter springs are under tension; use proper tools for removal.
Chemical Exposure	Use gloves when handling fuel, oil, or cleaning solvents.

WARNING! Failure to follow safety procedures can result in serious injury or death. Always refer to the operator's manual for general safety.

Specifications & Identification

• Model: HT 131
• Engine Type: 2-stroke, single cylinder, air-cooled
• Displacement: 31.8 cc
• Power Output: 1.6 kW (2.2 hp)
• Fuel/Oil Mix: 50:1 (STIHL HP Ultra oil recommended)
• Idle Speed: 2800 RPM
• Max. RPM: 13000 RPM (under load)
• Cutting Attachment: Uses STIHL Polycut or saw blade attachments
• Drive System: Flexible drive shaft within pole
• Gearhead Ratio: 1:1.6 (speed increasing)
• Serial Number Location: On engine housing near muffler

Tools & Special Equipment

Standard mechanic's tools plus Stihl special tools recommended for efficient repair.

1. Torx screwdrivers (T10, T15, T27)
2. Stihl piston stop tool (or equivalent)
3. Flywheel puller (Stihl 5910 890 4500)
4. Clutch removal tool (Stihl 0000 893 4303)
5. Spark plug wrench (Stihl 0000 893 5909)
6. Compression tester
7. Vacuum/pressure tester for crankcase
8. Feeler gauges
9. Torque wrench (2-20 Nm range)

Note: Using incorrect tools can damage components.

Engine Disassembly

Procedure to disassemble the powerhead for major repair.

1. Remove the starter assembly, air filter cover, and air filter.
2. Disconnect fuel line and remove carburetor.
3. Remove muffler and spark plug.
4. Secure crankshaft using piston stop tool, then remove clutch assembly with clutch tool.
5. Remove flywheel: Use puller after removing nut and washer.
6. Remove ignition module (coil).
7. Separate crankcase halves: Remove all screws, noting locations. Gently tap with plastic mallet to separate.

CAUTION! Mark crankcase halves for proper reassembly alignment.

Cylinder & Piston

Inspection and service of cylinder, piston, rings, and wrist pin.

Component	Inspection	Service Limit
Cylinder Bore	Check for scoring, wear, transfer. Measure diameter.	Max wear: 0.05mm out-of-round or taper.
Piston	Inspect skirt for scoring. Check ring grooves for wear.	Replace if scored or grooves widened.
Piston Rings	Check end gap in cylinder (measure at top of bore).	End gap: 0.25-0.45mm (new). Replace if over 0.8mm.
Wrist Pin & Bushing	Check for play and smooth rotation.	Replace if loose or shows wear.

Note: Light scoring can sometimes be cleaned with fine abrasive. Heavy damage requires replacement.

Crankshaft & Bearings

Inspect crankshaft, main bearings, and seals.

1. Check crankshaft runout: Support at ends, measure at center. Max runout: 0.03mm.
2. Inspect bearing races and balls for pitting or roughness. Replace if defective.
3. Check crankshaft seals for leaks (use pressure/vacuum test).
4. Inspect connecting rod big end bearing for radial play. Max play: 0.04mm.

WARNING! Do not attempt to straighten a bent crankshaft. Replace it.

Carburetor & Fuel System

Service the Zama C1Q-S carburetor (or equivalent).

1. Remove and disassemble carburetor. Note gasket and diaphragm order.
2. Clean all passages with carburetor cleaner and compressed air.
3. Inspect diaphragm and pump gasket for stiffness or tears. Replace kit (STIHL 0000 350 7005).
4. Check inlet needle and seat for wear.
5. Adjust idle (L) and high (H) speed screws to baseline: L - 1 turn open, H - 1 turn open from lightly seated.
6. Test fuel lines and filter. Replace if cracked or clogged.

Tip: Use a pressure test to check for internal carburetor leaks after reassembly.

Ignition System (MAGNETO)

Troubleshoot and service the electronic ignition module.

• Spark Test: Remove spark plug, connect to boot, ground against cylinder. Pull starter; look for strong blue spark.
• Air Gap: Between flywheel magnets and ignition module legs. Set to 0.30mm (0.012") using feeler gauge.
• Module Resistance: Primary coil resistance (plug wire to ground): approx. 1.5-3.0 kΩ. Significant deviation indicates failure.
• Flywheel: Check for cracks, damaged magnets, or keyway wear.

CAUTION! Never crank engine with spark plug disconnected and boot not grounded, as it can damage the ignition module.

Clutch & Drive Shaft

Service of centrifugal clutch and flexible drive shaft.

1. Remove clutch drum and inspect for wear or scoring.
2. Check clutch shoes for wear and spring tension. Replace if worn or springs are weak/broken.
3. Remove drive shaft from powerhead. Inspect for kinks, broken wires, or worn ends.
4. Lubricate drive shaft with STIHL drive shaft grease before reinstallation.
5. Check bearing in clutch drum for smooth rotation.

Note: Engagement RPM is controlled by clutch spring tension. Use genuine Stihl clutch assembly.

Pole Assembly & Gearhead

Disassembly and maintenance of the pole and gearhead.

1. Separate pole sections by unscrewing coupling nuts.
2. Remove gearhead from pole end. Disassemble gearhead housing.
3. Inspect gears (pinion and bevel) for broken teeth or excessive wear.
4. Check bearings and seals in gearhead. Replace if leaking grease or rough rotation.
5. Pack gearhead with high-quality grease (STIHL special grease).
6. Inspect pole interior for debris that could damage drive shaft.

WARNING! Do not operate with a damaged gearhead, as it can fail catastrophically.

Reassembly & Adjustment

Critical steps for reassembling the powerhead and final adjustments.

1. Assemble crankcase halves with new gasket. Torque screws in crisscross pattern to 10 Nm.
2. Install new crankshaft seals. Lubricate lips with grease.
3. Install flywheel: Torque nut to 35 Nm. Set ignition air gap.
4. Install clutch: Torque nut to 40 Nm (use piston stop).
5. Reinstall carburetor, fuel lines, air filter, and muffler.
6. Final Adjustments:
   • Set idle speed screw to achieve 2800 RPM (using tachometer).
   • Adjust H screw for smooth acceleration and maximum power without 4-stroking at full throttle under load.
   • Check chain oiler function (if saw attachment used).

CAUTION! Always perform a final operational check in a safe area before returning to service.

Troubleshooting Guide

Symptom	Possible Cause	Corrective Action
Engine won't start	No spark, flooded, fuel issue, compression low	Check spark, plug condition. Dry plug, choke off pulls. Check fuel line, filter, compression (should be >110 psi).
Engine starts then dies	Clogged fuel filter, carburetor issue, air leak	Replace filter. Clean/service carb. Pressure test crankcase for leaks.
Loss of power	Clogged air filter, exhaust screen, carb adjustment, worn piston/cylinder	Clean/replace filter, clean spark arrestor screen. Adjust carb. Check compression.
Excessive vibration	Damaged clutch/drum, bent drive shaft, loose components	Inspect clutch assembly. Check drive shaft. Tighten all mounting screws.
Cutting attachment doesn't turn	Broken drive shaft, clutch failure, gearhead failure	Inspect drive shaft. Check clutch engagement. Inspect gearhead gears.
Engine overheats	Lean fuel mixture, clogged cooling fins, improper lubrication	Adjust carb richer. Clean fins. Ensure correct fuel/oil mix.

Final Note: For complex issues or if in doubt, consult a Stihl authorized servicing dealer.

Service Support: STIHL Incorporated, 1-800-467-8445, www.stihlusa.com