Stihl Chainsaw 021 Service Manual
The Stihl Chainsaw 021 is a lightweight, professional-grade chainsaw designed for demanding cutting tasks. This service manual provides comprehensive information for maintenance, troubleshooting, and repair. It covers safety procedures, technical specifications, engine components, fuel system, ignition system, chain and bar assembly, carburetor adjustment, and routine servicing. Below are key sections for safe operation, maintenance schedules, component specifications, and step-by-step repair procedures.
Safety Information
Critical safety warnings and precautions for operating and servicing the Stihl 021 chainsaw.
| Hazard | Precaution |
|---|
| Kickback | Always use proper grip; maintain chain brake function; avoid contact with bar tip. |
| Fuel Handling | Use approved fuel containers; refuel in well-ventilated area away from ignition sources. |
| Chain Tension | Check tension before each use; adjust when chain sags from guide bar. |
| Personal Protective Equipment (PPE) | Wear safety glasses, hearing protection, gloves, chainsaw chaps, and sturdy boots. |
| Hot Surfaces | Allow engine and muffler to cool before performing maintenance. |
| Sharpening | Secure saw; use proper filing tools; maintain correct cutter angles. |
| Electrical Shock | Disconnect spark plug wire before servicing ignition components. |
| Fall Protection | When working aloft, use appropriate climbing gear and secure work area. |
| Two-Stroke Oil | Use only high-quality Stihl two-stroke engine oil at 50:1 mix ratio. |
| Bar & Chain Lubrication | Check oil reservoir level; ensure oiler port is clear for proper lubrication. |
Specifications & Technical Data
Detailed technical specifications for the Stihl 021 chainsaw.
- 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/Oil Mix: 50:1 (High-quality two-stroke oil with unleaded gasoline).
- 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 (Picco Micro Mini).
- Chain Gauge: 0.050" (1.3 mm).
- Ignition System: Electronic, breakerless.
- Spark Plug: Bosch WSR6F or equivalent, gap 0.5 mm (0.020").
- Idle Speed: 2,800 - 3,200 RPM.
- Maximum Power Speed: 9,500 RPM.
- Weight (powerhead only): 4.2 kg (9.3 lbs).
Maintenance Schedule
Recommended maintenance intervals for optimal performance and longevity.
- Before Each Use: Check chain tension, sharpness, and lubrication; inspect for loose fasteners; verify throttle and chain brake operation.
- After Each Use: Clean air filter; wipe down saw; check for damage.
- Every 10 Operating Hours: Clean spark arrestor screen; inspect fuel filter; check clutch and sprocket.
- Every 20 Operating Hours: Replace air filter; clean cooling fins; inspect anti-vibration elements.
- Every 50 Operating Hours: Replace spark plug; clean carburetor; check ignition timing.
- Every 100 Operating Hours: Replace fuel filter; inspect piston through exhaust port; decarbonize muffler.
- Seasonal: Drain fuel system for storage; perform complete inspection.
WARNING! Failure to follow maintenance schedule may result in premature wear, unsafe operation, or voiding of warranty.
Engine Components
Identification and function of major engine components.
Cylinder & Piston: Aluminum cylinder with chrome plating; single-ring piston. Crankshaft: Supported by ball bearings. Carburetor: Walbro or Zama diaphragm type with H, L, and LA adjustment screws. Ignition Module: Electronic CDI unit. Recoil Starter: Spring-return mechanism with pawls. Clutch: Centrifugal type, engages at approximately 2,800 RPM. Muffler: Includes spark arrestor screen.
Fuel System & Carburetor
Service procedures for fuel tank, lines, filter, and carburetor adjustment.
- Fuel Tank: Remove, clean, and inspect for cracks. Replace fuel cap gasket if leaking.
- Fuel Lines: Check for brittleness or cracks. Replace using ethanol-resistant lines.
- Fuel Filter: Located inside tank. Replace when clogged.
- Carburetor Adjustment (at operating temperature):
- Initial Settings: Turn H and L screws gently clockwise to stop, then counterclockwise 1 turn each.
- Idle Adjustment (LA screw): Adjust to achieve 2,800 - 3,200 RPM idle with chain not moving.
- Low Speed (L screw): Adjust for smooth acceleration from idle.
- High Speed (H screw): Adjust for maximum RPM not exceeding 9,500 RPM (use tachometer).
CAUTION! Improper carburetor adjustment can cause engine damage. Use a tachometer for precise H screw setting.
Ignition System
Testing and servicing the ignition coil, spark plug, and kill switch.
- Spark Plug: Remove, clean electrodes, check gap (0.5 mm / 0.020"). Replace if worn or fouled.
- Ignition Coil Air Gap: Set between 0.2 mm and 0.4 mm (0.008" - 0.016") using feeler gauge.
- Coil Resistance Test (primary): 0.5 - 2.0 ohms. (secondary): 8k - 16k ohms. Values outside range indicate failure.
- Kill Switch Test: Continuity should exist when switch is pressed; open circuit when released.
- Spark Test: Ground plug to cylinder; pull starter rope. Look for strong blue spark.
Tip: Always disconnect spark plug wire before performing any ignition system service.
Chain & Bar Assembly
Maintenance, sharpening, and replacement of cutting components.
- Chain Tension Adjustment: Loosen bar nuts. Adjust tensioning screw until chain fits snug against bar but can be pulled around by hand. Retighten bar nuts.
- Sharpening: Use correct round file size (typically 4.0 mm / 5/32"). Maintain 30° top plate cutting angle and 10° file tilt. Equalize file strokes on all cutters.
- Depth Gauge Setting: Use flat file and depth gauge tool. Set 0.65 mm (0.025") below top plate.
- Bar Maintenance: Clean bar groove; flip bar regularly for even wear; dress rails with flat file if burred.
- Sprocket Inspection: Replace drive sprocket if worn or damaged. Check rim sprocket for wear.
WARNING! A dull or improperly tensioned chain increases kickback risk and reduces cutting efficiency.
Troubleshooting Guide
| Symptom | Possible Cause | Corrective Action |
|---|
| Engine will not start | No spark, flooded, fuel issue | Check spark plug, ignition; wait if flooded; verify fuel mix and lines. |
| Engine starts then dies | Clogged fuel filter, carb adjustment | Replace fuel filter; adjust L screw; clean carburetor. |
| Lacks power under load | Clogged air filter, spark arrestor, carb H setting | Clean/replace air filter; clean spark arrestor; adjust H screw. |
| Chain does not turn | Clutch worn, sprocket damaged, chain brake engaged | Inspect clutch shoes and springs; replace sprocket; disengage chain brake. |
| Excessive vibration | Loose fasteners, unbalanced chain, AV mounts damaged | Tighten all fasteners; sharpen chain evenly; replace anti-vibration elements. |
| Chain throws oil | Overfilled oil tank, clogged oiler port | Drain excess oil; clean oil passage in bar pad. |
| Engine overheats | Dirty cooling fins, lean carburetor setting | Clean cylinder fins; check H and L settings for proper richness. |
Reset: For electronic issues, disconnect spark plug wire for 30 seconds to reset module.
Disassembly & Assembly
Key steps for major component removal and installation.
- Remove Top Cover: Remove two screws, lift cover off.
- Remove Starter Assembly: Remove screws, carefully lift starter to avoid spring tension.
- Remove Cylinder Cover: Remove screws, detach choke linkage.
- Remove Cylinder: Remove cylinder base nuts, gently lift cylinder off crankcase.
- Remove Piston: Remove circlip, wrist pin, and piston. Note orientation.
- Remove Clutch: Use clutch holding tool, turn clockwise (left-hand thread) to remove.
- Remove Oil Pump: Remove screws, lift pump assembly.
- Reassembly: Reverse sequence. Use new gaskets. Apply thread locker to critical fasteners.
CAUTION! Tag and organize all parts. Refer to torque specifications during reassembly.
Torque Specifications
Critical fastener torque values (Nm / in-lbs).
- Cylinder Base Nuts: 10 Nm (89 in-lbs).
- Spark Plug: 25 Nm (18 ft-lbs).
- Clutch Nut: 40 Nm (30 ft-lbs) - LEFT-HAND THREAD.
- Flywheel Nut: 40 Nm (30 ft-lbs).
- Guide Bar Nuts: 9-10 Nm (80-89 in-lbs).
- Muffler Screws: 8 Nm (71 in-lbs).
- Handlebar Mounting Bolts: 12 Nm (106 in-lbs).
- Anti-Vibration Buffer Nuts: 8 Nm (71 in-lbs).
Parts List & Diagrams
Reference for ordering genuine Stihl replacement parts.
Common Part Numbers:
- Air Filter: 0000 120 1605
- Spark Plug: Bosch WSR6F (Stihl 0000 400 1300)
- Fuel Filter: 0000 350 3501
- Carburetor Repair Kit: Walbro K10-WAT (or specific to carburetor model)
- Chain Brake Band: 0000 160 4501
- Clutch Assembly: 0000 160 4003
- Ignition Module: 0000 400 1305
- Piston Kit (including rings, pin, circlips): 0000 030 2005
Exploded View Diagrams: Available from authorized Stihl dealers or the official Stihl website using the model number (021) and serial number.
Service: For technical support and genuine parts, contact an authorized Stihl servicing dealer or visit www.stihlusa.com.
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