stihl 021 repair manual pdf

The STIHL 021 is a lightweight, professional-grade chainsaw designed for occasional to frequent use in forestry, landscaping, and property maintenance. This repair manual covers essential procedures for troubleshooting, maintenance, and repair of the STIHL 021 model, including the engine, fuel system, ignition, chain brake, clutch, guide bar, and cutting chain. Below are key sections for safety, specifications, troubleshooting, step-by-step repair procedures, and parts identification.

Safety Precautions

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

Specifications & Technical Data

Key technical data for the STIHL 021 chainsaw.

• Engine Type: Single-cylinder, two-stroke, air-cooled.
• Displacement: 31.8 cc (1.94 cu. in.).
• Power Output: 1.6 kW (2.1 hp).
• Fuel/Oil Mix: 50:1 (STIHL HP Ultra or equivalent).
• Guide Bar Lengths: 12" to 16" (30 cm to 40 cm).
• Chain Pitch: 3/8" PMM (Picco Micro Mini).
• Ignition: Electronic, breakerless.
• Weight (powerhead): 4.2 kg (9.3 lbs).
• Idle Speed: 2,800 rpm.
• Max Engine Speed: 13,500 rpm.

Troubleshooting Guide

Common operational issues and initial diagnostic steps.

1. Engine won't start: Check fuel (fresh mix), spark plug (clean/gap), ignition wire, carburetor adjustments, and air filter.
2. Engine starts then stalls: Inspect fuel line for cracks, fuel filter, carburetor diaphragm, and tank vent.
3. Loss of power: Clean spark arrestor screen, check compression, examine muffler for carbon buildup.
4. Chain doesn't turn: Verify clutch drum/spur sprocket, clutch springs, chain brake engagement, and drive sprocket wear.
5. Excessive vibration: Inspect anti-vibration mounts, balance of cutting assembly, and crankshaft bearings.

WARNING! Always diagnose with the engine off and spark plug disconnected.

Engine Repair

Procedures for cylinder, piston, crankshaft, and bearings.

1. Remove top cover, air filter, and carburetor.
2. Disconnect fuel lines and throttle linkage.
3. Remove cylinder cover and muffler.
4. Unbolt cylinder; inspect piston and cylinder walls for scoring.
5. Check crankshaft seals for leaks (common cause of lean run).
6. Reassemble with new gaskets; torque cylinder bolts to spec.

Note: Use a piston stop tool when removing flywheel or clutch.

Fuel System

Carburetor adjustment and fuel line replacement.

Carburetor (Zama C1Q-S series): Adjust idle (L), high (H), and idle speed screws. Standard baseline: L - 1 turn open, H - 1 turn open from lightly seated.

1. Remove carburetor; clean with compressed air.
2. Replace diaphragms and gaskets in kit.
3. Check fuel filter in tank; replace if clogged.
4. Inspect fuel lines for cracks or hardening.
5. Prime bulb (if equipped) for leaks.

CAUTION! Use only ethanol-resistant fuel lines.

Ignition System

Testing and replacing ignition module, spark plug, and flywheel.

Chain Brake & Clutch

Disassembly, inspection, and reassembly of safety and drive components.

1. Chain Brake: Remove side cover; inspect brake band for wear, spring tension, and handle mechanism. Replace if band is less than 0.5 mm thick.
2. Clutch: Use clutch removal tool; check shoes for wear, springs for fatigue. Clean clutch drum interior; replace spur sprocket if worn.
3. Clutch Drum Bearing: Inspect for smooth rotation; replace if gritty or noisy.

WARNING! The clutch assembly is under spring tension; use proper tools.

Guide Bar & Chain

Maintenance, repair, and replacement of cutting components.

• Bar Maintenance: Clean groove weekly; flip bar regularly for even wear; file down burrs on rails.
• Chain Sharpening: Use round file (4.0 mm) at 30°; maintain depth gauges with flat file.
• Chain Tension: Adjust so chain snaps back when pulled from bar.
• Sprocket: Replace spur sprocket every two chains or if visibly worn.

Tip: Always match chain pitch and gauge to bar specifications.

Maintenance Schedule

Recommended service intervals for optimal performance.

Parts Diagrams

Exploded views with part numbers for major assemblies (refer to official STIHL parts catalog for exact numbers).

1. Cylinder Group: 1128 020 1201 (Cylinder), 1128 030 2001 (Piston), 1128 007 1000 (Ring).
2. Carburetor Kit: 1128 007 1050 (Zama repair kit).
3. Clutch Assembly: 1128 640 2001 (Clutch), 1128 647 1800 (Spring).
4. Chain Brake Band: 1128 650 7701.
5. Ignition Module: 1128 400 1305.

Note: Part numbers may vary by serial number; verify before ordering.

Torque Specifications

Critical fastener torque values (Nm / in-lbs).

Use a calibrated torque wrench for accurate tightening.