STIHL 031AV Repair Manual

The STIHL 031AV is a professional-grade chainsaw known for its durability and power. This repair manual provides comprehensive instructions for maintenance, troubleshooting, and repair of the STIHL 031AV chainsaw, covering the engine, fuel system, ignition, chain brake, bar, chain, and other critical components. Below are key sections for safety, specifications, disassembly, repair procedures, and reassembly.

1. Safety Precautions 2. Specifications 3. Tools Required 4. Engine Disassembly 5. Cylinder & Piston Inspection 6. Carburetor Adjustment & Repair 7. Ignition System 8. Chain Brake System 9. Bar & Chain Maintenance 10. Reassembly Guide 11. Troubleshooting

Safety Precautions

Before performing any repair, ensure the chainsaw is turned off, spark plug wire disconnected, and all moving parts have stopped. Wear appropriate personal protective equipment (PPE).

Precaution	Description
Fuel Safety	Drain fuel tank before disassembly; work in well-ventilated area away from ignition sources.
Chain Safety	Ensure chain brake is engaged; wear cut-resistant gloves when handling chain.
Electrical Safety	Disconnect spark plug wire to prevent accidental starting.
Tool Safety	Use correct tools; do not force components during disassembly.
Workspace	Work on clean, stable surface; keep organized to avoid losing small parts.

Specifications

Engine Type: Single-cylinder, two-stroke, air-cooled.
Displacement: 49.0 cc (3.0 cu in).
Power Output: 2.5 kW (3.4 hp) at 8000 rpm.
Fuel/Oil Mix: 50:1 (STIHL HP Ultra or equivalent).
Ignition System: Electronic, breakerless.
Carburetor: Zama C1Q-S series.
Bar Length Options: 16", 18", 20".
Chain Pitch: 3/8" PM.
Weight (Powerhead): 6.2 kg (13.7 lbs).

Tools Required

Standard and specialized tools needed for repair.

STIHL combination wrench or socket set.
Torx screwdrivers (T27, T15).
Feeler gauge set (for spark plug gap).
Compression tester.
Piston ring compressor.
Chain breaker and spinner.
Carburetor adjustment tool.
Multimeter (for ignition testing).

WARNING! Use genuine STIHL tools or equivalents to avoid damage.

Engine Disassembly

Step-by-step guide to disassemble the engine.

Remove top cover and air filter cover.
Disconnect fuel line and remove carburetor.
Remove muffler and spark plug.
Remove cylinder cover and cylinder bolts.
Lift cylinder carefully; remove piston and connecting rod.
Remove clutch assembly and flywheel.

CAUTION! Label parts and take photos during disassembly for easier reassembly.

Cylinder & Piston Inspection

Check for wear, scoring, or damage.

Component	Inspection Criteria	Action if Failed
Cylinder Walls	Look for scoring, scratches, or excessive wear.	Replace cylinder or hone if within spec.
Piston Rings	Check ring end gap (spec: 0.3-0.5 mm).	Replace if out of spec or broken.
Piston Skirt	Inspect for scuffing or cracks.	Replace piston if damaged.
Wrist Pin & Bearing	Check for play or wear.	Replace if loose or worn.

Carburetor Adjustment & Repair

Adjusting and servicing the Zama carburetor.

Remove carburetor and clean with compressed air.
Check diaphragm and gaskets for cracks; replace if necessary.
Adjust idle speed screw (LA) and high-speed screw (H) to factory settings.
Set idle speed to 2800-3200 rpm.
Test run and fine-tune for smooth acceleration.

Tip: Use STIHL adjustment tool for precise tuning.

Ignition System

Testing and replacing ignition components.

Spark Plug: NGK BPMR7A, gap 0.5 mm.
Ignition Coil: Test resistance (primary: 0.5-1.5 Ω, secondary: 8-15 kΩ).
Stop Switch: Check continuity; replace if faulty.
Flywheel: Inspect for cracks; check key alignment.

WARNING! Always disconnect spark plug wire before testing ignition.

Chain Brake System

Inspect and repair the chain brake mechanism.

Remove side cover and clutch cover.
Check brake band for wear or cracks.
Inspect handle linkage and spring tension.
Test engagement; replace band if thickness < 1.5 mm.
Reassemble and test brake function before use.

Bar & Chain Maintenance

Maintain bar, chain, and sprocket for optimal performance.

Component	Maintenance	Frequency
Guide Bar	Clean groove, flip regularly, file rails if burred.	Every 10 hours
Chain	Sharpen cutters, check depth gauges, lubricate.	Every tank of fuel
Sprocket	Inspect for wear; replace if teeth are hooked.	Every 2-3 chains
Oil Pump	Check output; adjust or replace if not oiling.	Seasonally

Reassembly Guide

Reverse disassembly steps with attention to torque specs.

Install crankshaft bearings with proper sealant.
Install piston with ring compressor; arrow toward exhaust.
Torque cylinder bolts to 10 Nm (88 in-lbs).
Install flywheel and torque nut to 40 Nm (30 ft-lbs).
Reinstall carburetor with new gaskets.
Adjust carburetor and test run.

CAUTION! Use torque wrench to avoid over-tightening.

Troubleshooting

Symptom	Possible Cause	Corrective Action
Engine won't start	No spark, fuel issue, flooded	Check spark plug, fuel lines, carburetor; clear flood.
Loss of power	Clogged air filter, exhaust screen, carb adjustment	Clean/replace filter, clean spark arrestor, adjust carb.
Chain won't oil	Clogged oil passages, faulty pump	Clean oil ports, check pump drive, replace pump.
Excessive vibration	Loose components, unbalanced flywheel	Tighten bolts, check flywheel and clutch balance.
Chain brake fails	Worn brake band, weak spring	Replace brake band and/or spring.

Service: For technical support, contact STIHL authorized service center or visit www.stihlusa.com.