Stihl 021 Chainsaw Service Manual

The Stihl 021 is a lightweight, professional-grade gasoline chainsaw designed for demanding cutting tasks. This service manual provides comprehensive information for maintenance, troubleshooting, and repair. It covers the engine, fuel system, ignition, chain brake, guide bar, cutting chain, and all major components. Below are key sections for safety, specifications, maintenance procedures, troubleshooting, and parts identification.

Safety Precautions

Before performing any service, read and understand all safety warnings. Always wear appropriate personal protective equipment (PPE).

Specifications & Identification

Identify your saw using the serial number plate on the rear handle.

• Engine Type: Single cylinder, two-stroke, air-cooled.
• Displacement: 35.2 cc (2.15 cu. in.).
• Power Output: 1.8 kW (2.4 hp).
• Fuel Tank Capacity: 0.5 L (16.9 fl. oz.).
• Oil Tank Capacity: 0.26 L (8.8 fl. oz.).
• Guide Bar Lengths: 12" to 16" (30 cm to 40 cm).
• Chain Pitch: 3/8" PMM or .325".
• Ignition System: Electronic, breakerless.
• Carburetor: Zama C1Q-S series.
• Weight (powerhead): 4.6 kg (10.1 lbs).

Maintenance Schedule

Regular maintenance is critical for performance and safety. Follow this schedule based on hours of operation.

1. Daily/Before Use: Check chain tension, sharpness, and lubrication. Inspect for loose fasteners or damage.
2. Every 5 Hours: Clean air filter. Check spark plug condition.
3. Every 20 Hours: Replace fuel filter. Clean spark arrestor screen in muffler.
4. Every 50 Hours: Clean cylinder fins. Check clutch drum and sprocket for wear.
5. Every 100 Hours: Clean carburetor. Check fuel lines and impulse line for cracks.
6. Seasonal/Storage: Drain fuel tank and run carburetor dry. Store in a dry place.

WARNING! Use only genuine Stihl parts and recommended lubricants. Failure to do so may void warranty and cause unsafe operation.

Fuel & Lubrication System

Use a high-quality 2-stroke engine oil mixed with unleaded gasoline at a 50:1 ratio (2% oil).

1. Fuel System Components: Tank, cap, filter, fuel line, carburetor.
2. Chain Oil System: Oil tank, pump, delivery line, outlet, adjustable flow.
3. Fuel Filter Replacement: Disconnect fuel line, remove old filter, install new filter, reconnect line.
4. Oil Pump Adjustment: Turn adjusting screw (located near clutch) to increase/decrease oil flow.
5. Testing Oil Flow: Run saw at high speed with bar tip aimed at a light surface; a line of oil should appear.

CAUTION! Never use automotive motor oil or mixed fuel older than 30 days.

Engine & Ignition System

Access engine components by removing the top cover and air filter housing.

Cylinder & Piston: Inspect for scoring. Measure compression (should be > 120 psi).

Ignition: Check spark plug gap (0.020" / 0.5 mm). Test ignition module with multimeter per specifications.

Muffler & Spark Arrestor: Remove and clean screen regularly to prevent overheating.

Rewind Starter: Inspect rope and spring. Re-wind spring carefully during assembly.

Chain Brake & Clutch

The chain brake is a critical safety device. Test function before each use.

1. Chain Brake Engagement: Manually push front hand guard forward; chain should stop immediately.
2. Brake Band Inspection: Check for wear or glazing. Replace if thickness is below specification.
3. Clutch Inspection: Remove clutch drum. Check clutch shoes for wear and springs for integrity.
4. Centrifugal Clutch Operation: Shoes engage at approximately 2,800 RPM.
5. Sprocket: Replace spur sprocket or rim sprocket when worn to prevent chain damage.

Tip: Clean clutch area of wood chips and oil residue to ensure proper operation.

Guide Bar & Cutting Chain

Proper chain tension is when the drive links are seated in the bar groove and the chain can be pulled around by hand with slight resistance.

1. Bar Maintenance: Clean bar groove daily. Flip bar weekly for even wear. Dress bar rails with a flat file if burred.
2. Chain Sharpening: Use correct round file size (typically 4.0 mm or 5/32"). Maintain correct filing angle (30°).
3. Depth Gauge Setting: Use a depth gauge tool to set raker height (typically 0.025" / 0.65 mm below cutter).
4. Chain Replacement: Match pitch, gauge, and drive link count. Ensure cutting direction is correct.
5. Tensioning: Loosen bar nuts, adjust tensioning screw, retighten nuts with bar tip lifted.

WARNING! A loose or dull chain is dangerous and increases kickback risk. Always stop the engine before adjusting tension.

Carburetor Adjustment

Adjustment screws: L (low speed), H (high speed), LA (idle speed). Initial settings: Turn L and H screws gently clockwise until seated, then back out 1 turn.

1. Preliminary: Ensure air filter is clean and fuel is fresh.
2. Idle Speed (LA): Adjust so chain does not move at idle and engine accelerates smoothly.
3. Low Speed (L): Adjust for smooth acceleration from idle without hesitation.
4. High Speed (H): Adjust for maximum RPM without exceeding specified no-load speed (approx. 13,500 RPM). Use a tachometer.
5. Final Check: Engine should return to idle quickly after a high-speed burst. Chain must not move at idle.

CAUTION! Over-leaning the H screw can cause engine seizure. If unsure, seek professional service.

Disassembly & Assembly

General sequence for major service. Refer to detailed exploded-view diagrams.

1. Remove top cover, air filter, and carburetor cover.
2. Disconnect fuel and impulse lines. Remove carburetor.
3. Remove starter assembly, ignition module, and muffler.
4. Remove cylinder cover nuts. Carefully separate cylinder from crankcase.
5. Remove piston pin circlips and pin to remove piston.
6. For crankcase separation, special tools are required. This is an advanced procedure.
7. Assembly: Reverse order. Use new gaskets and seals. Apply appropriate sealant to crankcase halves.

Torque Specifications

Use a calibrated torque wrench. Do not overtighten.

Troubleshooting

Reset: For electronic ignition issues, no user reset is available.

Service: For technical support or genuine parts, contact your local authorized Stihl dealer or visit www.stihlusa.com.