STIHL 021 Service Manual

The STIHL 021 is a compact, two-stroke chain saw designed for homeowners and light professional use, combining reliable performance with a user-friendly design. Its compact size makes it easy to handle in tight spaces, while still delivering solid cutting power for routine yard work and small- to medium-sized felling tasks. Built by STIHL, a brand renowned for durability and engineering, the 021 emphasizes balance, vibration control, and straightforward maintenance, which helps extend the tool’s service life when operated with proper care. The model typically features a lightweight magnesium or alloy housing and a robust air-cooled engine that can run on standard fuel mixtures, making it accessible for regular use without excessive weight or complexity. For longevity, attention to chain oiling, air filtration, and spark plug maintenance is essential, as consistent upkeep reduces downtime and improves cutting efficiency over the life of the saw.

Key features of the STIHL 021 include a dependable two-stroke engine that offers a solid power-to-weight ratio, enabling efficient cuts without excessive fatigue. It usually incorporates a side-access chain tensioner, which simplifies adjustments in the field, along with STIHL’s advanced anti-vibration system to reduce operator fatigue during prolonged use. The saw is designed with an easy-start or semi-automatic starting mechanism to simplify ignition, especially after the tool has been stored or used in cooler conditions. A bar and chain combination is selected for balanced performance, and the tool typically includes a manual fuel shutoff and a clean air filtration system to maintain engine reliability. Safety features such as a chain brake, front handguard, and proper chain lubrication ensure a controlled and safer operation during routine tasks like limbing, pruning, and small-diameter felling.

Common applications for the STIHL 021 cover a broad range of home, farm, and light professional tasks. This model excels at cutting firewood, trimming branches, and tackling small-scale removal jobs where maneuverability is critical. It is well-suited for maintaining hedges, clearing brush, and performing routine maintenance around property lines where a larger saw would be impractical. Because of its compact size, it is often chosen by homeowners who require precise control in confined spaces, such as near buildings, fences, or undergrowth. When paired with the appropriate chain speed and depth gauges, the 021 can deliver clean, efficient cuts with minimal kickback, provided the operator adheres to safe handling practices and uses the correct protective equipment. Proper chain tension, bar replacement intervals, and regular inspection of the air filter and spark plug are essential to ensure consistent performance in these typical applications.

Personal protective equipment (PPE) requirements are essential for safe operation and maintenance of the STIHL 021. Operators should wear cut-resistant gloves to protect hands from sharp edges and hot surfaces, safety glasses or goggles to shield eyes from flying debris and fuel splashes, and hearing protection to mitigate prolonged exposure to engine noise. In addition, a respirator or dust mask is recommended when cutting, sanding, or grinding materials that generate fine particulates, and sturdy, non-slip footwear should be worn to reduce the risk of slips and foot injuries. Long-sleeved clothing and a sturdy belt or holster for tools help minimize exposure to moving parts and fuel spills. Ensure all PPE is inspected before use and kept clean and in good repair to maintain their protective capabilities during service tasks.

Work area preparation and safety practices are critical to prevent accidents and injuries during service and maintenance of the STIHL 021. The workspace should be well-ventilated with unobstructed access to a sturdy workbench, adequate lighting, and a clear, organized tool storage area to minimize trip hazards. Remove any flammable liquids, solvents, and fuel from the immediate vicinity to reduce fire risk, and ensure a functioning fire extinguisher is readily available. When working with the engine or fuel system, perform tasks away from ignition sources and on a non-combustible surface. Establish a routine for securing the unit, disconnecting the spark plug boot, and draining fuel when applicable to prevent accidental starts during servicing. Maintain a clean environment by sweeping up oil spills promptly and disposing of waste materials in accordance with local regulations.

Pre operation checks and maintenance tasks include a systematic inspection of the saw’s critical systems before starting any service procedure. Verify that the air filter is clean and undamaged, the spark plug is properly gapped and free of fouling, and the muffler and exhaust path are clear of obstructions. Check the fuel system for leaks, cracked hoses, and proper fuel mixture, and ensure the fuel cap seals correctly. Inspect the chain brake, clutch cover, and bar nuts for proper tension and secure fastening, and confirm that the chain is sharp, properly lubricated, and free of excessive play. Record any irregularities and address them according to the manufacturer’s guidelines before proceeding with further maintenance tasks to prevent damage or injury.

The STIHL 021 engine requires a careful and deliberate approach to starting to ensure a smooth and safe operation. Begin by inspecting the spark plug, air filter, and fuel system for any signs of wear or leaks before attempting a start. Confirm that the choke, throttle, and on/off switch are in their correct positions according to the manufacturer’s recommendations. Ensure the chain brake is engaged and the bar and chain are free of obstructions. When priming is required, use the primer bulb as specified, avoiding harsh or excessive pumping to prevent flooding. A proper starting procedure also involves maintaining a steady stance, securing a firm grip, and keeping hands and clothing away from the bar and chain during the initial ignition sequence. After starting, allow the engine to warm up briefly while monitoring for any unusual noises or vibrations that could indicate a fault.

Operating the STIHL 021 for efficient cutting and a consistent feed rate involves coordinating throttle control, cutting speed, and bar-rail alignment. Begin with a comfortable, balanced posture and maintain a steady rhythm that matches the resistance of the wood. Engage the chain brake when repositioning or moving between cuts, and release it only when you are prepared to drive the saw through the next cut. Use smooth, long strokes rather than forcing the chain, which can cause unnecessary wear and increased fuel consumption. Keep the chain sharp and properly tensioned, and perform regular checks for fuel mix accuracy and lubrication oil flow to ensure consistent performance. In all operations, stay mindful of kickback zones and operate with a clear escape path to reduce the risk of injury.

Handling different wood types and cutting scenarios requires adjustments in technique and feed rate to optimize both safety and efficiency. Softer woods, such as pine, typically allow for faster cutting with moderate chain speed, but still require careful control to prevent bar pinching. Hardwoods, like oak or maple, demand a slower feed rate and more deliberate, controlled cuts to avoid overtaxing the motor and chain. In wet or damp conditions, reduce feed rate and verify that the cutting path remains dry to prevent slippage and loss of control. For large-diameter timber, plan multiple progressive cuts to remove material incrementally rather than attempting a single, high-resistance pass. Always align cuts with the natural grain when feasible and avoid binding by maintaining consistent chain tension and an unobstructed cutting line. By adapting the operating procedure to wood type and cutting scenario, you can maximize both safety and cutting efficiency without compromising engine longevity.

The STIHL 021 requires a structured routine to ensure reliable performance and long service life. Establishing a clear maintenance schedule helps prevent unexpected failures and keeps your saw operating at peak efficiency. Begin with daily checks that include fuel levels, bar and chain lubrication, and overall cleanliness. Weekly or every-ten-hours inspections should focus on air filtration, chain tension, and chain sharpening status. Monthly tasks are more thorough, involving a closer look at the cooling system, spark plug condition, and fuel lines. Adhering to this cadence minimizes downtime and promotes safer, more consistent operation over the life of the saw.

Lubrication and fuel system care are critical for smooth operation and longevity. Use fresh, clean fuel mixed to the manufacturer’s specified ratio and inspect the fuel cap for proper sealing to prevent moisture ingress. Regularly check the oiling system to ensure the bar and chain receive adequate lubrication, especially during heavy cuts or when using longer bars. Inspect fuel and oil lines for cracks, leaks, or signs of hardening, and replace any suspect components promptly. Maintaining proper lubrication reduces wear on the bar, chain, and piston rings, and helps maintain consistent cutting performance.

Air filter and cooling system maintenance prevent overheating and power loss. Remove the air filter and clean it or replace it according to the operating environment and usage. A dirty filter restricts airflow, leading to richer mixtures and potential carbon buildup. While the filter is out, inspect the cooling fins and fan area for debris and clean them without damaging delicate components. Ensure the cooling system remains free of obstacles, and verify that the starter and cooling passages are clear. Regular attention to these areas sustains engine efficiency and reduces the risk of thermal related failures during demanding work.

Spark plug and ignition system service are essential for reliable starts and efficient combustion. Remove and inspect the spark plug for signs of wear, fouling, or improper gap, and replace it if necessary with the correct heat range recommended by STIHL. When reinstalling, ensure the plug is tightened to the specified torque and that the ignition coil connections are clean and secure. Periodic checks of the ignition system, including flywheel timing marks and spark gap verification, help prevent misfires and hesitations under load. A well-maintained ignition system contributes to smoother starting, consistent power delivery, and longer overall engine life.

Carburetor adjustment and tuning require careful, methodical adjustments to maintain optimal fuel-air mixtures. Begin with the manufacturer’s baseline settings and adjust in small increments while monitoring engine response under load. Be mindful of altitude, temperature, and fuel quality, as these variables necessitate subtle changes to idle speed, high-speed mixture, and low-speed adjustment. Use the correct tools and avoid forcing components; engine performance should improve with each precise adjustment. After any carburetor work, recheck compression, throttle response, and emissions indicators to confirm the engine runs cleanly and efficiently across the operating range.

Chain maintenance and bar inspection are fundamental for safe and effective cutting. Regularly check chain tension according to the tool’s guidelines, ensuring the chain remains snug but able to move freely by the bar nose. Inspect the drive sprocket, chain links, tie straps, and cutting teeth for wear, cracks, or damage, replacing any compromised sections promptly. Examine the guide bar edge and cutter rails for burrs, excessive side play, or signs of bending, and rotate or replace the bar if wear becomes uneven. When sharpening, maintain equal angles and bevels across all teeth to preserve balanced cutting performance and reduce vibration that can affect operator control.

Section Troubleshooting And Common Problems

When diagnosing issues with the STIHL 021, begin with a careful, systematic evaluation of the most common failure points. A thorough inspection of the air intake, fuel system, and ignition system can reveal the root cause of many symptoms before more invasive testing is required. Record the observed conditions, including starting attempts, idle behavior, and any abnormal noises or vibrations, to establish patterns that guide subsequent steps. Remember to disconnect the spark plug boot and follow proper safety procedures whenever working near the air intake and fuel components to prevent accidental starting or fuel exposure. A clean, organized work area with appropriate tools and a clear marking of parts that require replacement will streamline the troubleshooting process.

No start or difficult starting is frequently linked to fuel quality, carburetor configuration, or ignition timing. Start by confirming that the fuel mix matches the manufacturer’s specifications and that the fuel is fresh, not older than 30 days in typical storage conditions. Inspect the carburetor for varnish buildup and ensure that the choke, throttle, and primer are functioning correctly. A wobbly or weak spark can also impede starting; test the ignition coil and spark plug for proper gap, wear, and fouling. If the engine responds to a quick spray of primer but stalls after, investigate possible air leaks in the intake manifold or carburetor mounting, as these leaks can lean out the mixture and prevent reliable starting.

Loss of power or performance issues often indicate clogged filters, restricted cooling, or air-fuel delivery problems. Check the air filter for excessive dirt and replace if necessary to restore proper airflow. Examine the spark plug for color and deposit patterns that reveal fuel richness or lean conditions, adjusting the carburetor needle accordingly within the recommended range. Inspect the muffler for carbon buildup, which can restrict exhaust flow and reduce power output. Ensure the fuel line is free of cracks or leaks, and confirm that the fuel is reaching the carburetor without significant resistance. A test run after these inspections can determine whether the performance improves or if deeper carburetor cleaning and jet maintenance are required.

Chain binds or stalls are typically caused by improper bar and chain maintenance or incorrect cutting tension. Begin by turning off the unit and allowing the chain to stop completely before inspecting for embedded debris, bar wear, or a tight chain. Confirm that the sprocket nose and guide bar are in good condition and that the chain brake is functioning correctly. Check the chain alignment along the bar groove and verify the correct chain tension as specified by STIHL’s guidelines. If binding occurs during cutting, inspect the wood for knots or very hard material that can grab the chain, and consider slowing the feed rate to maintain smooth operation. Frequent binding can indicate a misadjusted carburetor or an internal engine issue that requires professional assessment.

Unusual noises or vibrations often signal mechanical wear or loose components. Listen for knocks, rattles, or scraping sounds that may originate from the clutch, drive shaft, or bar mounting hardware. Tighten any loose screws, bar nuts, or mounting bolts to appropriate torque values as recommended by the service manual. Excessive vibration can stem from a bent bar, unequal chain tension, or worn drive components, so examine the bar for straightness and replace worn parts as needed. If noise changes with throttle position, perform a controlled test to isolate whether the source is the clutch, the bar, or the engine itself. Persistent abnormal sounds should prompt a professional inspection to prevent further damage.

Electrical or fuel system faults encompass a range of issues from ignition misfires to faulty sensors and dead circuits. Begin with a visual inspection of wiring harnesses for fraying, loose connections, or insulation damage, ensuring all connectors are seated firmly. Use a multimeter to check the continuity of ignition wires and to confirm proper voltage supply to the ignition coil and spark plug. Fuel system faults may involve a clogged fuel filter, a weak fuel pump, or air leaks that disrupt the fuel-air mixture; replace or clean components as indicated by diagnostic readings. Finally, inspect the recoil starter mechanism for binding or resistance that could mimic electrical faults; a smooth, consistent pull indicates that the mechanical components are functioning correctly. Document all findings and replace any worn or damaged parts to restore reliable operation.

Disassembly should begin with a clear, organized workspace that is free of clutter and has ample lighting. Before any tools touch the saw, remove the battery or disconnect the spark plug to prevent accidental starts. Confirm that the chain brake is engaged and the bar is away from the clutch so no movement can occur during the procedure. Document each part as it is removed, keeping track of fasteners and fitment to avoid confusion during reassembly. Use the appropriate hand protection and eye protection, and work on a non-slip mat to prevent tool or component loss in the event of minor slips. Maintain a clean, well-lit environment throughout the process to ensure you can inspect small components for wear or damage as they are exposed.

Removing the chain and bar should be performed with the bar cover removed and the chain loosened to relieve tension safely. Place the bar and chain in a controlled area to prevent chipping teeth or bending the bar rails. Use the correct size socket or wrench to loosen the bar nuts, and avoid applying excessive force that could strip threads or crack the bar mounting area. When the chain is free, carefully lift the bar and save the bar spacers separately to ensure correct reinstallation later. Inspect the drive sprocket and bar groove for wear, replacing the bar if the groove is excessively worn or if the drive sprocket shows hooked or flat spots. Maintain a record of fastener locations and any washers or spacers removed to facilitate precise reassembly.

Engine air and carburetor related disassembly requires careful attention to the intake boot, air filter, and carburetor mounting hardware. Disconnect the fuel line with proper containment to prevent spills, and drain the fuel system into an approved container. Remove the air filter housing and inspect the air filter for dirt or damage, replacing if necessary to prevent lean or rich running conditions. When removing the carburetor, mark or photograph linkage positions to ensure correct orientation during reassembly, and handle the carburetor with care to avoid damage to the throttle slide or needle. After removal, inspect the intake manifold for cracks or warping, and check the fuel lines and clamps for signs of wear, tightness, or leakage. Reassemble components in the reverse order, paying close attention to gasket seating and the potential need for a new seal or O-ring to maintain proper pressure and fuel delivery.

Reassembly steps and torque specifications must be followed meticulously to restore proper function and safety. Begin with seating the crankcase components and torquing bolts to the manufacturer’s specified values using a calibrated torque wrench, ensuring even distribution of clamping force. Reinstall the carburetor with new gaskets if required and secure all fasteners to the specified torque. Reinstall the air intake system, ensuring a proper seal between the filter housing and the carburetor, and verify that the air filter is clean and properly oriented. Reattach the bar and chain assembly with the correct sequence of spacers and the bar nuts tightened to the specified torque, confirming that the chain tension is within the recommended range. Complete this step by reinstalling the recoil assembly or ignition module as applicable, ensuring proper alignment and secure mounting to prevent timing or starting issues.

Post service testing and safety checks are essential to confirm the unit operates correctly and safely after disassembly and reassembly. Start the unit in a well-ventilated area, observing for any unusual noises, smoke, or vibrations that could indicate a misassembly. Check for proper chain tension, clutch engagement, and bar lubrication by performing a brief idling test and a light rev test, avoiding full-throttle operation until all systems are confirmed stable. Inspect the fuel line connections and carburetor for leaks after running the engine briefly, and recheck all fasteners for tightness once the saw has cooled. Verify that the chain brake functions correctly by engaging and releasing it during idle and slight movement to ensure it safely stops the chain. Finally, perform a functional safety test on the ignition and stop switch, confirming that the engine stops promptly when commanded and that all safety interlocks remain intact.

Section Specifications And Reference

The STIHL 021 chainsaw represents a compact, two-stroke, air-cooled engine platform designed for light to mid-range cutting tasks. This section provides a concise yet comprehensive overview of the technical specifications, operating parameters, and the essential maintenance reference points necessary for safe and reliable service. Understanding these fundamentals helps technicians diagnose performance issues accurately and apply the correct service procedures without unnecessary risk to the operator or the equipment. Accuracy in torque values, gap tolerances, and fuel mixtures is critical to maintaining peak performance and longevity of the saw’s rotating components and exhaust system. This overview is intended to establish a solid baseline for more detailed diagnostic and repair work conducted in subsequent steps.

The engine on the STIHL 021 employs a proven two-stroke design that relies on a precise fuel mixture for optimal combustion, lubrication, and power delivery. Key specifications include displacement, bore and stroke measurements, compression ratio, maximum RPM, idle speed, and recommended operating temperatures. Electrical ignition is typically a magneto-based system, with no battery requirement for standard operation. The carburetor provides fine-tuning for altitude and temperature changes, ensuring steady idling and responsive throttle control. Recognizing these specifications allows a technician to verify correct factory settings after maintenance procedures such as overhaul, carburetor adjustments, or ignition troubleshooting.

The tool's lubrication strategy depends on an oil-to-fuel premix that ensures adequate lubrication of the transmission and engine internals. The correct premix ratio and quality of oil play a significant role in minimizing wear and preventing scuffing of the piston and bearings. A thorough check of the oil delivery path, including the oil metering system and lines, is essential when diagnosing startup or lubrication-related smoking and overheating symptoms. Adherence to the manufacturer’s lubrication guidelines supports consistent power output and reduces the likelihood of premature failure due to inadequate lubrication under high-load conditions. Proper cooling through unobstructed air circulation is also a critical supportive factor in maintaining engine performance during extended use.

Replacement parts and part numbers are documented by the OEM to ensure compatibility, reliability, and warranty compliance. Commonly requested components include spark plugs, fuel filter, air filter, carburetor rebuild kits, gaskets, seals, and the cooling fan assembly. Verifying part numbers before ordering prevents misfits that can lead to improper sealing, fuel leakage, or compromised ignition timing. When performing preventive maintenance, stock replacement filters and consumables should be matched to the exact model year and production batch, as revisions may introduce improved materials or fitment. Reference to the official STIHL parts catalog is recommended to confirm current part numbers and any service advisories that may affect replacement intervals or procedure steps.

In addition to the core specifications, a technician should maintain a log of service intervals, observed performance trends, and any deviations from standard measurements. This documentation supports trend analysis for predictive maintenance, helps isolate recurring issues, and provides a foundation for warranty claims if applicable. A structured approach to recording engine temperature, ignition timing checks, and fuel mixture consistency enables more efficient future diagnostics. The integration of these data points into a service history strengthens the reliability and safety of the STIHL 021 in everyday use and professional settings.

Overall, Section Specifications And Reference consolidates the essential facts needed to perform accurate inspections, routine maintenance, and careful part selection. By aligning service practices with the documented specifications, technicians can uphold performance standards, extend saw life, and ensure safe operation for users in varied environments. This foundation supports more advanced repair scenarios, including carburetor tuning, ignition troubleshooting, and transmission checks, by ensuring every step begins from a precise understanding of the machine’s designed parameters and official component compatibility.

The information herein should be used in conjunction with hands-on manufacturer guidance and current service bulletins. Always follow safety protocols, disconnect the spark plug boot before performing any disassembly, and verify that the saw is on a stable surface with the bar and chain secured. When in doubt about a specification or replacement part, consult the STIHL official parts database or contact authorized service technicians to prevent incorrect maintenance actions that could compromise performance or operator safety.

In practice, technicians should cross-reference each maintenance action with the model’s technical specifications, confirming that torque values, fitment clearances, and lubrication routes conform to the manufacturer’s standards. This disciplined approach minimizes the risk of fuel or air leaks, reduces chain brake malfunctions, and supports consistent cutting performance. The combination of accurate specifications, correct lubricants, and properly identified replacement parts forms the backbone of a dependable service routine for the STIHL 021, ensuring it remains reliable and safe for years of operation in a variety of cutting tasks.

Section Appendices And Documentation

The maintenance log templates provide a structured way to track all service activities performed on the STIHL 021. Each template is designed to capture critical data such as date of service, operator initials, hours of operation, parts replaced, and a concise description of the work completed. Maintaining a thorough log assists in scheduling routine maintenance, identifying recurring issues, and verifying compliance with preventive maintenance intervals recommended by the manufacturer. For best results, incorporate a space for noting any observed wear patterns and potential future corrective actions. Regularly updating these templates supports consistent performance and can simplify warranty or service history reviews during future diagnostics.

Warranty information outlines the terms, limitations, and requirements associated with the STIHL 021. It typically covers defects in materials and workmanship for a specified period from the date of purchase when the equipment is used in normal operation and properly maintained. The documentation often outlines exclusions such as damage caused by misuse, improper maintenance, or unauthorized alterations. It is essential to retain proof of purchase and to follow all recommended service intervals to preserve warranty eligibility. Understanding the warranty details helps technicians and owners make informed decisions about repairs, parts replacements, and service planning when issues arise.

Manufacturer service advisories provide timely guidance on known issues, updates, and recommended corrective actions issued by STIHL. These advisories may address modifications to procedures, part revisions, or safety considerations that affect how the 021 should be serviced. Reading and applying advisory information ensures that maintenance and repairs align with current manufacturer expectations, which can improve reliability and reduce the risk of intermittent failures. Technicians should document the implementation of advisories in the service log, noting the advisory reference number, date, and any parts or process changes made as a result. Keeping these advisories up to date contributes to a safer and more predictable operating life for the equipment.