STIHL MS 291 Service Manual

Overview of stihl ms 291 service manual

The STIHL MS 291 is a mid-range chainsaw designed for demanding cutting tasks while balancing reliability and ease of maintenance. This section provides a concise overview of engine specifications, compatibility, and the core considerations a technician should observe during service. Understanding these fundamentals helps ensure accurate diagnosis, proper parts selection, and safe operating performance after any repair or routine maintenance. A clear grasp of the tool’s baseline specifications also informs service intervals and the appropriate lubricants, fuels, and consumables required for optimal operation. Proper interpretation of these details reduces the risk of incorrect assembly and enhances overall system longevity.

Engine specifications and compatibility are foundational for effective service. The MS 291 employs a two-stroke, air-cooled engine designed to run on a standard STIHL fuel mixture, with specific compression and timing characteristics that influence starting procedures and power output. Compatible components include the air filter, carburetor, ignition module, crankshaft, piston, and exhaust system, each selected to match OEM tolerances. When performing maintenance or parts replacement, technicians should verify part numbers against official documentation to ensure compatibility, especially when sourcing aftermarket alternatives. This careful verification helps maintain performance benchmarks such as idle stability, throttle response, and peak power delivering consistent cutting performance. In addition, compatibility checks extend to bar and chain configurations, chain pitch, and sprocket sizes, which collectively impact safe operation and guide maintenance routines.

Safety guidelines and personal protective equipment (PPE) are integral to every service procedure. Prior to inspection or disassembly, ensure the engine is cool, the spark plug is disconnected, and the chain brake is engaged to prevent unintended motion. PPE should include cut-resistant gloves, eye protection, hearing protection, and sturdy footwear suitable for workspace hazards. The manual emphasizes working in a well-ventilated area to avoid exposure to fuel vapors, with a ready supply of absorbent material for any spills and a fire-safe workspace free of ignition sources. During disassembly, follow step-by-step procedures to avoid damaging seals and gaskets, and use torque values from the manufacturer to prevent overtightening. Documentation of wear patterns, abnormal noises, or degraded components helps establish maintenance history and guides decisions about repairs versus replacement, all while prioritizing operator safety throughout the service process.

The STIHL MS 291 portable chainsaw requires a reliable set of hand tools and power tools to perform routine maintenance, diagnostics, and repair tasks efficiently. Beginning with basic hand tools, a quality set of metric and SAE combination wrenches, a screwdriver set with various blade types, torx bits, and a sturdy adjustable wrench will cover most fastener sizes found on the saw. Precision feeler gauges and small pliers or needle-nose pliers assist in adjusting components without causing damage, while a soft mallet or rubber hammer helps seat parts gently during reassembly. A torque wrench is essential for reattaching fasteners to the proper specification, preventing over-torque damage to critical joints. Finally, a clean, lint-free rag and degreasing solvent are useful for removing old lubricant and preventing contamination of the fuel and air systems.

In addition to hand tools, purpose-built power tools accelerate service work while reducing the risk of component damage. A high-quality cordless drill or impact driver with a shallow-depth setting makes chain brake and clutch work more efficient, while a small scraper or wire brush attachment helps remove built-up carbon from cooling fins and the muffler area. A digital multimeter can verify electrical continuity and assess sensor or switch integrity when diagnosing electrical faults or abnormal engine behavior. An infrared thermometer or surface temperature tool can help monitor exhaust and cylinder temperatures during running diagnostics, providing a quick read on potential overheating issues. Properly rated handheld air compressor accessories, including a small nozzle and a bit of compressed air, assist in cleaning ports and cooling channels without introducing contaminants into the engine.

The specialized diagnostic instruments and test procedures for the MS 291 focus on accurate measurement and safe evaluation of operating parameters. A service-specific spark plug tester or replacement plug toolkit ensures correct gap and heat range, which is crucial for reliable ignition and optimum performance. A fuel pressure gauge and a uniform test fuel supply allow precise assessment of the carburetor and fuel delivery system under different load conditions. Vacuum gauges and manometers are used to evaluate intake manifold pressure for diagnosing carburetor tuning or air leak issues, especially after gasket or seal replacements. When testing ignition electronics, a spark tester is invaluable for confirming spark quality and timing under load, reducing guesswork during repairs. Finally, a wrench-on vacuum gauge kit paired with diagnostic tubes helps isolate and confirm leaks in the intake system, muffler, and fuel line connections, ensuring that repair work yields a stable and predictable running condition.

Starting and running procedures

Before attempting to start the STIHL MS 291, perform a thorough pre-start inspection to ensure safe and reliable operation. Check for fuel leaks, cracked fuel lines, and secure connections at the fuel tank and carburetor. Inspect the air filter for excessive dirt or damage, and replace it if needed to prevent unfiltered air from entering the engine. Verify that the chain brake is disengaged and that the bar and chain are properly mounted with the chain tension within specifications. Ensure the spark plug is clean and properly gapped, and confirm that the muffler and cooling fins are free of obstructions. A clean, dry, and tightened assembly reduces startup friction and improves running stability from the first pull.

Starting procedures require attention to the fuel system, which for the MS 291 uses a two-stroke mix. Confirm the correct fuel-oil ratio as specified in the manual, typically a high-quality two-stroke oil mixed with unleaded gasoline. Use fresh fuel and avoid ethanol blends if possible, as ethanol can affect fuel system components over time. Prime the carburetor according to the model’s specific priming technique, usually by pressing the primer bulb several times until a slight resistance is felt. Avoid over-priming, which can flood the carbuetor and hinder starting. With the engine at a neutral position, set the choke as recommended for cold starts, and prepare for the starting sequence with a firm stance and controlled pulls to minimize kickback and ensure safe operation.

Following the starting sequence, observe normal running parameters to establish a baseline for engine performance. The MS 291 should reach its normal operating temperature after a few minutes of light to moderate load. Monitor for smooth idling behavior and consistent pull-through of the starter rope without excessive effort. Check for stable RPMs and listen for odd noises such as knocking or pinging, which can indicate fuel or timing issues. If the engine runs rough or stalls, avoid forcing a restart; instead, re-check the fuel mixture, air filter condition, spark plug color, and muffler for obstructions. Once warmed, gradually apply throttle to ensure the chain remains stationary when instructed by the operator’s manual safety features, and confirm that the chain brake engages and disengages as designed when necessary for safe operation during startup and idle conditions.

In routine operation, maintain appropriate running parameters to optimize performance and extends the life of the saw. Use a proper bar oil level and ensure consistent lubrication to reduce bar and chain wear during cutting operations. Monitor exhaust emissions and sound levels as indicators of engine health; excessive smoke or unusual odors may signal rich or lean fuel mixtures or exhaust system issues that require attention. Keep the air intake free of debris to prevent overheating and loss of power. Regularly inspect the cooling fins and remove any accumulated sawdust to maintain efficient heat dissipation. By adhering to these practices, you achieve reliable starting, smooth running, and predictable performance across typical cutting tasks.

If the saw fails to start or shows degraded performance, consult a troubleshooting guide for common starting issues and resolutions. Typical problems include flooded carburetor from improper priming, a fouled spark plug, a clogged air filter, or fuel system blockages. Resolve flooding by allowing the engine to rest briefly while keeping the choke in the disengaged position, then perform a careful restart with the correct choke setting. Replace a fouled or worn spark plug and clean the ignition area to ensure a strong spark. When air restriction is suspected, clean or replace the air filter and inspect the fuel line for cracks or leaks. If fuel delivery or carburetor issues persist, professional servicing may be required to recalibrate or service internal components to restore proper starting and running characteristics.

Regular maintenance is essential for dependable starts and consistent operation of the STIHL MS 291. Schedule routine inspections of the fuel system, air filtration, ignition system, and exhaust pathway, including muffler and spark arrestor if present. Document service dates and observed symptoms to track patterns that may indicate wear or impending failure. Practicing proper startup routines, clean components, and timely repairs will help minimize downtime and extend the service life of the equipment, ensuring safe and efficient performance on demanding cutting tasks.

Fuel system maintenance and troubleshooting

The fuel system of the STIHL MS 291 is designed to deliver a precise air-fuel mixture for optimum engine performance and longevity. Ensuring correct fuel mixture specifications protects against excessive internal wear, carbon build-up, and starting difficulties. Begin by confirming the recommended fuel formulation, typically a two-stroke mix of gasoline and 2-cycle oil at the correct ratio prescribed by STIHL. It is essential to use fresh gasoline and a high-quality 2-cycle oil to maintain proper lubrication and to minimize varnish formation within the carburetor and fuel lines. Regular inspection of the fuel system should include checking for signs of fuel leaks, cracking hoses, or degraded seals, as these issues can lead to air leaks and improper mixture dynamics. Maintaining seal integrity is crucial, as worn gaskets or O-rings can cause lean or rich conditions that affect engine performance and create excessive exhaust emissions.

Carburetor inspection and adjustment require meticulous attention to both the external and internal components. Begin by removing the carburetor carefully and inspecting the float, needle valve, and metering orifices for wear, pitting, or dirt buildup. If the engine runs inconsistently, idles roughly, or dies under load, it may indicate improper carburetor calibration or gasket leaks. Use the manufacturer’s recommended diagnostic procedures to verify correct idle speed, low-speed, and high-speed jet settings, and adjust only within these tolerances. When rebuilding, replace gaskets, seals, and the diaphragms with OEM parts to prevent air leaks and ensure reliable throttle response. After adjustments, reassemble with careful alignment of the linkage and ensure the fuel-to-air mixture remains stable across operating temperatures and elevations. Regular carburetor maintenance also includes priming the system correctly and verifying that the primer bulb functions without allowing air into the fuel line.

Fuel filter and line replacement procedures require a methodical approach to prevent contaminants from entering the carburetor and causing performance issues. Inspect the fuel filter for clogging, soft spots, or frayed fabric, and replace it if any degradation is observed. When replacing lines, cut to exact lengths with clean, square cuts to avoid kinking and to ensure a proper seal at barbed fittings. Use fresh fuel and a clean container during the replacement process to minimize particulate contamination. After installing new lines and filters, inspect all clamps and fittings for secure connections and absence of leaks. It is prudent to perform a pressure test of the fuel supply if the equipment permits, which helps identify leaks or weak connections that could impair efficiency. Regular preventive maintenance of the fuel system reduces the risk of hard starts, surging, and erratic operating behavior, extending the life of the engine and the saw’s overall performance.

Air system and filtration service

The air system on the STIHL MS 291 plays a critical role in engine performance, fuel efficiency, and long-term reliability. Begin with a careful inspection of the air intake path, including the air filter housing, connecting boots, and any clamps or fasteners. Look for cracks, signs of wear, or loose connections that could allow unfiltered air or debris to enter the carburetor. A thorough assessment ensures the engine receives clean air and operates within its designed parameters. When performing maintenance, always work in a clean environment to prevent contaminants from entering the air pathway during disassembly and reassembly.

For proper carburetor air reference and boot inspection, reference the routing of the air intake from the air filter to the carburetor throat. Inspect the carburetor boot for elasticity and cracks, particularly at aging joints or where heat and vibration are most intense. A brittle boot can cause vacuum leaks, leading to fluctuating idle, reduced power, or difficult starting. If the boot shows any significant deformation, tears, or hardening, replace it with the correct OEM part to maintain a proper seal and consistent air delivery to the carburetor. When reassembling, ensure all mating surfaces are clean and free of debris that could compromise the seal or introduce contaminants into the intake tract.

Regarding filter replacement interval and technique, follow a scheduled maintenance plan that aligns with operating conditions, dust exposure, and runtime. The air filter should be inspected at every service interval and replaced when visible dirt, oil saturation, or reduced airflow is detected. Use the recommended paper or foam filter elements and avoid over-tightening clamps or housings, which can distort the filter and impede airflow. When installing a new filter, ensure the lips seal evenly against the housing and that the filter sits squarely within its channel. Keep a log of replacement dates and hours to track service life and prevent performance degradation due to restricted air intake. Regular maintenance of the air filtration system contributes to efficient combustion, reduced engine wear, and extended tool longevity in demanding outdoor conditions.

Lubricant types and change intervals

Proper lubrication is essential to maintain the STIHL MS 291’s engine efficiency and longevity. Use the recommended bar and chainsaw oil, ensuring it meets the manufacturer’s viscosity specification for your ambient temperature range. Regularly check the oil reservoir level before each use and top up as needed to maintain consistent lubrication during operation. Depending on usage, plan for oil changes at specific service intervals or after a set number of running hours, replacing contaminated oil to prevent carbon buildup and sludge formation. Always inspect the oil line and pump thoroughly during routine maintenance, looking for cracks, leaks, or blockages that could impede oil delivery to the bar and chain. When replacing the oil, purge the system to remove air pockets, ensuring a steady flow to prevent uneven lubrication and accelerated wear on the bar and chain. In dirty or dusty environments, increase the frequency of checks to compensate for faster oil degradation and potential contamination. Consider recording oil consumption and interval data to help establish a personalized maintenance schedule that fits your cutting conditions and work pace.

Cooling fins cleaning and overheat prevention

Efficient cooling is crucial to prevent overheating and maintain optimal engine performance. Regularly inspect the cooling fins for dirt, sawdust, resin, and small debris that can insulate the engine and impede heat transfer. Use low-pressure compressed air or a soft brush to remove obstructions from between the fins without bending or damaging them. After cleaning, recheck the fin surfaces for any signs of damage, such as nicks or cracks, and address them promptly to preserve airflow. Ensure the cooling air intake is clear and unobstructed, as restricted air can dramatically raise operating temperatures and shorten engine life. Monitor operating temperatures during heavy use and pause to allow the saw to cool if you notice unusual warmth or power loss, which can indicate restricted cooling or fuel issues. For high-demand tasks, consider performing a cooldown after extended cutting sessions to prevent thermal stress on the cylinder and piston assembly. Regular cooling system maintenance, combined with clean air pathways, supports consistent performance and a longer service life for the MS 291 platform.

The ignition system on the STIHL MS 291 is a critical component that delivers a reliable spark to ignite the air-fuel mixture in every cylinder cycle. Regular inspection of the spark plug, ignition coil, and related wiring helps prevent misfires and hard starting, especially under varying weather conditions and thermal loads. Begin by removing the spark plug boot carefully and inspecting the porcelain for cracks, fouling, or a characteristic oily residue that indicates oil intrusion. Clean or replace the spark plug as needed, ensuring the electrode gap matches the manufacturer’s specification. When replacing the plug, torque to the recommended value and apply a light anti-seize compound if specified by STIHL. After reinstalling, perform a quick resistance check on the ignition coil and spark plug boot to confirm continuity and absence of excessive resistance that could weaken the spark.

Inspecting timing reference marks is essential for ensuring the engine remains in proper synchronization between the crankshaft position and the ignition event. Before checking marks, remove any debris from the flywheel cover and align the saw to a safe position to prevent accidental starts. Use a proper tool to view the timing marks on the flywheel and matching indicators on the crankcase or flywheel housing. If marks are misaligned, you may need to adjust the stator or timing stop components according to the service data, making sure to recheck clearances and fastener torque after any adjustment. It is important to confirm that the engine has the correct timing under both idle and full-throttle conditions, as discrepancies can lead to reduced power, increased fuel consumption, and potential engine damage over time. Always perform a cautious test run after adjustments to verify smooth running and consistent ignition timing across the RPM range.

Timing reference marks and adjustments require meticulous attention to detail because even small deviations can impact engine performance. Start by turning the engine to the appropriate standing position and double-checking that the compression is within normal limits, which helps ensure that timing checks reflect true mechanical alignment. When interpreting timing marks, compare them against the STIHL specification for the MS 291 and note any wear or damage to the flywheel key that could cause timing drift. If you observe recurring timing drift, inspect the stator magnet, flywheel, and keyway for deformation or wear, replacing components as necessary to restore proper timing reference. After any adjustment, rotate the assembly through several complete cycles to confirm that the marks realign consistently, and recheck the spark plug firing condition to confirm ignition is synchronized with piston position. Adhering to these steps preserves engine efficiency, reduces emissions, and extends the life of the ignition system components.

Exhaust system inspection and maintenance

The exhaust system on the STIHL MS 291 is a critical component for performance, emissions, and user safety. Regular inspection helps prevent muffler degradation, exhaust leaks, and spark arrestor buildup that can impair engine efficiency and pose fire hazards. Begin with a visual and tactile check of the muffler housing for cracks, corrosion, or loose mounting hardware. Pay particular attention to the exhaust outlet flange where heat stress can cause gasket failure or warping. If any signs of damage or excessive carbon buildup are present, plan for replacement or professional service before proceeding with further operation. Always ensure the unit is cool and the spark plug is kept clear of any conductive debris during inspection. Muffler condition and spark arrestor service should be performed with the engine off and the fuel system depressurized. Remove the muffler carefully using the appropriate wrenches, taking care not to drop fasteners into the internal passages. Inspect the muffler for perforations, delamination, or melted insulation material that could restrict exhaust flow or alter backpressure. The spark arrestor screen must be free from soot, hot spots, and corrosion to maintain proper flame arresting capability. Clean the screen using a soft brush and a rust-inhibiting solvent if necessary, then reassemble with the correct torque to the mounting studs. If the screen is damaged or the internal baffles show signs of wear, replace the muffler assembly to preserve engine performance and safety. After reassembly, run the engine briefly to ensure there is no exhaust leak audible from the inlet or outlet joints and verify that mounting hardware remains secure. Port and gasket inspection is essential to maintain optimal exhaust flow and seal integrity. Remove the spark plug boot and carefully detach the muffler to expose the exhaust ports and intake interfaces. Look for any scoring, warping, or carbon buildup inside the port areas that could restrict flow or cause hot gas pockets. Inspect the intake and exhaust gasket surfaces for nicks, indentations, or hardened residues that could compromise the seal. If gasket material appears worn or damaged, replace with OEM gaskets matched to the MS 291 specification, ensuring clean mating surfaces prior to reassembly. When reinstalling, apply a light coat of anti-seize compound on threaded fasteners as recommended by STIHL service guidelines and torque them to the specified values. Finally, perform a cautious test run in a controlled environment, listening for abnormal exhaust sounds or leaks that would indicate insufficient seal or port obstruction, and address any issues before resuming regular operation.

Safety devices and chain brake servicing

The STIHL MS 291 relies on an integrated safety system to protect the operator from kickback and contact with the cutting chain. Regular inspection of safety devices ensures they deploy correctly under load and respond reliably during unexpected situations. Begin with a visual and functional check of the chain brake lever, ensuring it moves freely, returns to the neutral position, and engages the chain brake fully when rotated or released. Verify that the brake band and components do not show signs of excessive wear or damage that could impede engagement or cause unintended movement during operation. A clean, dry environment during inspection helps prevent contaminants from masking wear or deformation that could compromise performance.

Chain brake inspection and function test: This test confirms that the chain brake engages promptly when activated and that it remains engaged under simulated kickback conditions. With the chain in a non-cutting state and the engine idling, apply the chain brake and confirm that the chain stops within a short, observable distance. Remove the spark plug boot for safety and perform a brief test to ensure the brake lever physically engages the brake band and arrests the chain’s rotation. If the chain does not stop promptly, inspect the brake band for wear, glazing, or contamination, and check the brake housing for cracks that could affect alignment. After testing, reassemble all safety components securely and verify that the chain brake deactivates only with intentional operator input.

Chain catcher and clutch cover maintenance: The chain catcher serves as a backup protection in the event of chain derailment or brake failure, and the clutch cover protects the clutch mechanism from debris. Inspect the chain catcher for cracks, deformation, or looseness, ensuring it is firmly mounted to the chassis and aligned with the guide bar. Remove the clutch cover and examine the cover screws for proper torque and thread integrity, replacing any stripped or damaged fasteners as needed. Clean any buildup of pitch, resin, or sawdust from the interior surfaces of the clutch cover to prevent interference with clutch operation or chain movement. When reinstalling the cover, confirm that the chain brake components remain unobstructed and that the cover seating is even to maintain correct chain alignment and braking performance.

During routine maintenance, verify that all safety devices remain correctly positioned relative to the bar tip and drive sprocket. Confirm the brake handle resistance feels consistent across its travel and that returning the lever to its resting position does not leave the chain brake partially engaged. If any abnormal binding, excessive play, or inconsistent brake response is detected, remove the bar and chain assembly and inspect the brake housing, brake band, and return springs for wear or damage. Replace worn parts with OEM components to maintain the integrity of the safety system and ensure reliable operation under load.

The clutch, drive system, and sprocket assembly on the STIHL MS 291 are critical for efficient power transfer and safe operation. Regular inspection of these components helps prevent unexpected failures and costly downtime. Begin by checking for any signs of unusual wear, heat discoloration, or glazing on the clutch drum and shoes, as these can indicate improper engagement or an overworked engine. Ensure the drive sprocket teeth show even wear and are free of burrs or hooked edges that could damage the chain. When removing the clutch and sprocket assembly for inspection, follow the manufacturer’s torque specifications and use the correct tools to prevent misalignment or reassembly issues. After reassembly, verify that the chain moves freely around the bar with the engine off, and that there is no binding or excessive resistance in the clutch engagement mechanism.

The clutch inspection and replacement process begins with isolating the bar and chain for safety, then removing the cover and any shielding to access the clutch bell and drum. Carefully inspect the clutch springs, shoe linings, and the drum for wear patterns or cracks, replacing any components that show damage or significant wear. When replacing the clutch drum or shoes, ensure that the friction surfaces are clean and free of oil or fuel residue, as contaminants can compromise grip and cause slippage. After new parts are installed, lubricate only where specified by STIHL’s service guidelines and torque all fasteners to the recommended values. A test run should follow to confirm smooth engagement and to listen for any abnormal noises that could indicate misalignment or incorrect part seating. Always discard any used parts that show glazing, scoring, or delamination, since reusing worn components can lead to sudden clutch failure.

Drive sprocket wear is typically indicated by hooked teeth, rounding of the tooth profile, or chips along the tooth edge, which can cause chain derailment or uneven cutting. Begin by removing the sprocket cover, securing the saw against movement, and using the correct socket or bearing puller to remove the sprocket from the crankshaft; follow the reverse steps for installation. Compare the sprocket’s teeth to the original specifications and replace if the tooth profile is no longer within tolerance or if there is visible elongation of the mounting bore. When installing a new drive sprocket, clean the crankshaft sprocket interface and apply a thin, even coat of silicon-based or STIHL-approved lubricant to aid seating and prevent corrosion, avoiding any lubricant on the chain or bar. After installation, rotate the chain by hand to ensure it tracks properly over the sprocket and that there is no wobble or binding at the bearing surface. Finally, reassemble the cover and test the saw at a low idle to verify that power transfer remains consistent and that there is no unusual noise during acceleration or deceleration.

For ongoing reliability, establish a routine maintenance schedule that includes periodic inspection of clutch springs, shoe wear, drum surface condition, drive sprocket tooth integrity, and proper tensioning of the chain. Document wear measurements with a caliper or micrometer to track progressive wear over time, and replace components before they reach the end of their service life. Maintain clean, dry conditions in the tool storage area to slow corrosion and keep mating surfaces free of debris. When conducting any service work, always consult the STIHL MS 291 service manual for torque specifications and sequence recommendations, and employ the correct replacement parts to preserve performance and safety. Regular professional inspections can extend the life of the drive system and help maintain consistent cutting performance across demanding forestry tasks.

Bar and chain maintenance and tuning

Maintaining the bar and chain on a STIHL MS 291 is essential for safe operation, efficient cutting, and prolonged tool life. Begin with a thorough inspection of the chain to identify any dull teeth, chipped cutting edges, or uneven sharpening. A properly sharpened chain should have a consistent hook angle and file marks that are uniform across all cutters. When in doubt, remove the bar and chain assembly and inspect the drive links, plate thickness, and the rivets for signs of wear or elongation. Regular cleaning of the bar groove and oil holes ensures proper lubrication and minimizes heat buildup during operation.

Chain tensioning and lubrication require careful calibration to balance performance and safety. After the engine has cooled, loosen the bar nuts and snug the bar to prevent misalignment during tensioning. Use a tension gauge or measure by pulling the chain away from the guide bar at the midpoint; there should be a slight sag without binding, typically a few millimeters depending on the model. Lubrication is controlled by the oiling system, which should deliver a steady stream of oil to the chain while cutting; inspect the oil inlet hole on the bar and confirm that the oil can flow freely. Verify that the oiler reservoir is filled to the recommended level and that the oil passages are clear of obstructions, as insufficient lubrication accelerates chain and bar wear and increases the risk of kickback. After adjusting tension, rotate the bar by hand to ensure smooth operation and confirm that the chain seats properly in the bar groove without binding on the rivets.

Bar wear assessment and replacement require a careful measurement of the bar rails, groove, and nose sprocket alignment. Inspect the bar rails for excessive side-to-side wear, which can cause the chain to track improperly and increase strain on the engine. A worn groove can be detected by a noticeable widening of the groove width or irregularities along the cutting edge of the chain. The nose sprocket should rotate freely without wobble, and the bar nose tip should not be rounded or chipped. If the groove depth or bar rails show significant wear, or if the bar shows heat discoloration or warping, replace the bar to maintain proper chain alignment and cutting efficiency. When installing a new bar, ensure that it is compatible with the MS 291 model and that the bar mount holes align correctly with the studs and nuts to maintain precise alignment and reduce vibration during operation.

Riving knife alignment and safety checks are a critical part of bar and chain maintenance. The riving knife should be securely mounted and aligned to prevent the chain from binding into the bar groove during cutting, especially when engaging through the workpiece. With the chain removed or secured in a safe manner, inspect the alignment by ensuring the riving knife sits flush against the bar near the drive links without creating a gap that could trap wood fibers. Verify that the riving knife does not protrude beyond the bar's edge, which could cause interference with the chain or wood. Perform functional tests on a cutting task to confirm that the chain maintains correct tracking and that the riving knife actively reduces kickback potential by guiding the wood away from the chain path. If any misalignment is observed, adjust the rake or replace the riving knife per the manufacturer’s specifications to restore proper safety clearance and cutting efficiency.

The STIHL MS 291’s electrical system is relatively straightforward, but proper diagnosis requires careful inspection of the kill switch, wiring harness, and ignition components. Start with a visual check of all wiring harness connections for signs of wear, corrosion, or pinched conductors. Look for frayed insulation, melted sleeves, or damaged connectors that could cause intermittent loss of power or false readings. When inspecting the kill switch, ensure that the actuator engages fully and that the wiring from the switch to the ignition module is secure and undamaged. A loose or contaminated kill switch can cause abrupt shutdowns or failure to start, so test continuity with a multimeter when suspicious. Always disconnect the spark plug boot before handling electrical components to prevent accidental starts and ensure safe service procedures.

To troubleshoot common electrical faults effectively, establish a baseline by testing for spark, fuel delivery, and compression, since electrical issues can masquerade as ignition problems. Use a basic spark test by grounding the spark plug against a known good metal surface and cranking the engine to verify a strong, blue spark. If the spark is weak, fouled, or absent, inspect the ignition coil, magnetic flywheel ring, and its magnet for damage or misalignment, as a compromised magnetic interaction can reduce ignition strength. Inspect the on/off switch wiring and the kill switch circuit for continuity and correct resistance values as specified in the service data. Any unexpected resistance or open circuit requires replacing the faulty harness segment or connectors to restore reliable operation.

Further, assess the electronic timing and ignition module for signs of overheating or moisture ingress, which can cause erratic firing or complete failure to start. Check the ignition module mounting for security and ensure that any insulating barriers remain intact to prevent short circuits. If the engine experiences intermittent starting, verify that the wiring harness ground is solid and free of corrosion at the grounding point. A poor ground can manifest as mis-timed ignition events or stalling under load. After performing repairs or replacements, recheck all connectors for proper seating and secure any loose wires with compliant clips or ties to prevent future abrasion. End with a functional test by performing a controlled start and run cycle, monitoring for smooth acceleration, consistent ignition, and absence of detection codes or abnormal behavior in the engine’s performance.

Vibration and alignment service

Proper vibration control and bar alignment are essential for safe, efficient operation of the STIHL MS 291. Begin by performing a thorough inspection of the guide bar, bar studs, and mounting surfaces to identify any wear, bending, or looseness that could contribute to excessive vibration. Check the bar nose and edges for burrs or uneven wear, as these factors can alter the alignment and create uneven cutting forces. Ensure that the bar mounting surfaces on the saw body are clean, flat, and free of debris before reinstalling the bar and chain. Worn or damaged components should be replaced with genuine STIHL parts to maintain optimal performance and safety margins. After reassembly, rotate the bar by hand to confirm that it sits flush against the bar studs and the clutch cover studs without gaps or binding.

Guide bar alignment and bar studs are critical for maintaining straight cuts and reducing operator fatigue. To verify alignment, position the bar so that the chain sits squarely along the guide groove and check that the bar edges align evenly with both sides of the chainsaw body. Tighten the bar nuts to the manufacturer’s specified torque in a crisscross sequence to ensure even seating and to prevent induced stresses that could affect vibration characteristics. Inspect the bar studs for wear, rounding, or elongation, as these conditions can lead to bar misalignment and increased vibration. If any studs or mounting holes show signs of wear, replace them with new components and recheck alignment after installation. Periodic measurement of the bar groove width and the depth of the bar rails can help determine when the bar is nearing the end of its service life and should be replaced.

Anti-vibration system inspection and replacement involve examining the interaction between the engine mounting, the chassis, and the handles designed to dampen engine-induced oscillations. Start by visually inspecting the anti-vibration elastomer mounts for cracks, deformation, or hardening, and check for oil contamination that can degrade their performance. Wiggle the handles and body to detect any looseness that could indicate worn isolators or failing mounts; any movement beyond manufacturer tolerances should prompt replacement. Use the correct reinstall torque values for all hardware involved in the anti-vibration system and ensure that screws and nuts are threaded cleanly and secured to spec. If the engine mounting bolts show signs of elongation or the rubber bushings exhibit excessive deformation, replace the entire anti-vibration assembly or the defective components to restore proper damping and reduce operator fatigue. After replacement, perform a controlled test run to verify that vibration levels are within expected range and that the saw handles smoothly without excessive vibration transfer to the operator’s hands and arms.

Storage and long term care

Proper storage and long-term care of your STIHL MS 291 chainsaw helps ensure reliable starting, safe operation, and extended service life. Before placing the saw into storage, perform a thorough inspection and address any signs of wear, damage, or leakage. Clean all surfaces thoroughly to remove dust, sap, oil residues, and debris that can cause corrosion or attract moisture over time. Pay special attention to the cooling fins and air intake to prevent crusted buildup that could impede airflow when you resume use.

Seasonal storage steps and fuel stabilization are essential for preserving fuel system components. Drain or stabilize the fuel according to local regulations and manufacturer recommendations to prevent gum formation in carburetors and fuel lines. If you use fuel stabilizer, mix it with fresh gasoline at the recommended concentration and run the engine for several minutes to circulate the treated fuel through the carburetor. For longer storage periods, consider removing the battery (if applicable) and storing it in a cool, dry place away from direct sunlight, verifying that the battery terminals are clean and free of corrosion before reinstallation.

When storing the saw for an extended period, empty the fuel tank if the fuel is old or stale, and seal or cap the tank to prevent moisture ingress. Inspect the bar and chain for rust or dullness, and either remove the chain and bar for separate storage or cover them to protect from dust. Apply a light coat of bar and chain oil to the chain to prevent rust and preserve lubrication pathways, ensuring the chain brake and riving knife are clean and uncorroded. Store the saw in a dry, well-ventilated area, ideally on a rack or in a protective case to minimize accidental damage and to limit exposure to extreme temperatures.

Battery and spark plug storage considerations require careful handling to maintain performance and readiness for the next use. Remove the spark plug if you are storing the saw for an extended period and check it for signs of wear or fouling; replace if necessary and store it in a dry, insulated bag to prevent moisture exposure. If the saw uses a rechargeable battery, store the battery at approximately 40–60 percent charge in a cool, dry environment, away from heat sources that could degrade capacity. Periodically inspect the battery for voltage and integrity during long storage, and recharge to the recommended level before reinstallation. Clean the spark plug boot and terminal connections prior to storage to prevent corrosion and ensure quick, reliable startups when you return to operation.

Additional long-term care tips include protecting all exposed metal surfaces with a light rust preventative suitable for light-duty motorized tools, and keeping the air filter housing clean and free of pests or nesting material during storage. Ensure that the pull-start mechanism remains free of oil and debris and test its operation periodically to confirm it retracts smoothly. If the saw will not be used for several months, rotate the chain periodically to prevent stiffening and ensure that the drive sprocket teeth remain in good condition. Finally, keep a record of storage conditions and any maintenance performed, so you have a clear history to reference when you resume operation, helping you identify potential issues before they become failures.

When reactivating after storage, perform a thorough pre-start inspection following the manufacturer’s guidelines. Check for fuel, air, and exhaust system cleanliness, verify that the chain is properly tensioned and sharpened, and confirm that the bar is free of burrs or deformation. Start the engine with the saw held in a stable position, and listen for abnormal sounds that could indicate internal wear or contamination. If any issues arise during startup or initial operation, halt use and consult a qualified technician or the official service manual to avoid damage and ensure continued safety and reliability.

Troubleshooting quick reference

The following guidance provides rapid diagnostics for common STIHL MS 291 issues based on symptom observation, likely causes, and practical recovery steps. Begin with a calm assessment of the symptom and confirm basic conditions such as fuel health, air flow, and chain brake status before proceeding to more in-depth checks. Document any observed patterns or recurring symptoms to help refine future maintenance and prevent recurrence. Always follow safe starting procedures and depressurize the system as required when performing inspections that involve fuel or hot surfaces. This quick reference is designed to be used in the shop or in the field to get the saw back to working condition efficiently.

Symptom to probable causes mapping

A common symptom is the engine failing to start or hard starting. Probable causes include an empty or stale fuel mixture, a clogged fuel filter, a fouled spark plug, or an insufficient compression due to intake or exhaust restrictions. Another frequent issue is the engine starting but running poorly or dying soon after start; this can indicate carburetor maladjustment, contaminated fuel, or air leaks in the carburetor boot or intake gasket. If the chain does not move when the trigger is pulled, verify that the chain brake is disengaged, the throttle lockout is functioning, and there is adequate chain tension. For reduced power or poor cutting performance, inspect the air filter for dirt, confirm the muffler is not obstructed by carbon buildup, and ensure the spark plug gap remains correct. A chainsaw that runs but vibrates excessively may have loose muffler screws, a damaged bar, improper chain tension, or a misadjusted idle; verify all mounting hardware and chain alignment, and check the bar for heat or wear signs. If fuel leaks or wants to leak after startup, inspect the fuel line connections, fuel tank seals, and the carburetor seals for signs of wear or damage. In cases of excessive smoke or fuel smell, examine the carburetor settings, fuel quality, and the presence of any oil-rich fuel mixtures that could indicate a faulty oil metering system. When the chain fails to move smoothly or stalls under load, assess chain sharpness, tension, and bar condition, as well as the drive sprocket for wear. Finally, a saw that overheats quickly requires checking for clogged cooling fins, blocked air intake, or a pinched muffler, as well as ensuring proper ventilation during operation.

Step by step recovery flow for common issues

Begin with a visual and mechanical sweep of the exterior to identify obvious faults like loose screws, damaged fuel line clamps, or a loose chain. If starting problems are present, start with fuel quality and freshness; replace old fuel with a fresh, properly mixed fuel and replace the fuel filter if needed. Remove the spark plug, inspect for fouling, and clean or replace it as appropriate, ensuring the correct gap specification. Check the air filter for cleanliness and replace it if it shows signs of heavy dirt or damage. Inspect the carburetor for any signs of clogging or air leaks; if necessary, perform a careful carburetor cleaning or service, following STIHL service recommendations. Verify the intake boot, carburetor gaskets, and seals for wear and reseal if leaks are detected. With the engine running, observe exhaust flow and muffler condition for carbon buildup; clean or replace as required to restore proper back pressure. If the chain does not move, confirm the chain brake is disengaged, the throttle trigger is functioning, and the chain tension is appropriate; adjust if necessary. Inspect the drive sprocket and the centrifugal clutch for wear or damage and replace components that show excessive wear. In case of overheating, pause operation, remove material buildup from cooling fins and air intake, and ensure adequate clearance around the saw during use to promote proper cooling. Finally, perform a test run under light load, gradually increasing to full speed to confirm that the issue is resolved and that the saw maintains stable idle and smooth acceleration. Document all steps taken and test results to assist future maintenance and troubleshooting efforts.

The STIHL MS 291 is a robust chainsaw designed for mid to heavy-duty cutting tasks, and maintaining it on a rigorous service schedule is essential for reliable performance and safety. Regular service intervals help ensure optimal engine efficiency, dependable starting, and prolonged component life. Establishing a consistent routine for inspection, cleaning, and part replacement minimizes downtime and reduces the likelihood of unexpected failures in the field. A structured approach to maintenance also preserves fuel efficiency and reduces emissions, contributing to a safer and more productive work environment. Adhering to manufacturer-recommended intervals in conjunction with on-site usage patterns will yield the best balance between uptime and reliability.

Regular service intervals should be aligned with hours of operation, working conditions, and the type of wood or material being cut. At a minimum, perform a thorough inspection of the air intake, filter, and cooling fins after every major job or every few hours of operation in dusty conditions. Clean or replace the air filter as needed, and inspect the saw chain for proper tension, sharpness, and wear. Check ignition components, fuel system connections, and the spark plug for signs of fouling or wear, and replace them according to the manufacturer’s recommendations. Routine checks of the guide bar, sprocket, and chain oiling system help prevent uneven wear and ensure smooth operation, particularly under heavy-load tasks. Maintaining proper fuel mixture and using fresh, high-quality fuel minimizes internal deposits and extends engine life.

Additionally, perform periodic lubrication of movable parts such as the clutch components, handle mounts, and throttle linkage to prevent binding or premature wear. Keep the cooling system clear of debris to avoid overheating, especially during prolonged use in hot environments. Always verify that safety features, such as the chain brake and chain catcher, function correctly before starting the saw, and replace any worn or damaged parts promptly. Document the results of each inspection and maintenance task to establish a clear service history that supports warranty compliance and resale value. A proactive approach to maintenance reduces the likelihood of sudden outages and helps ensure consistent performance across different cutting tasks.

Logbook templates and record keeping are essential tools for capturing maintenance activities, parts replacements, and service dates. A well-structured log should include fields for date, hours of operation, technician name, and a concise description of the maintenance performed. Recording part numbers, batch codes, and gendered specifications of components such as filters, spark plugs, bars, and chains enables precise parts tracking and simplifies future ordering. Photographs or scanned copies of receipts and warranty documents can be linked to each service entry for quick reference and audit readiness. Regularly reviewing the log helps identify recurring issues, schedule preventive replacements before failures, and plan budget for upcoming maintenance cycles. In practice, a standardized template ensures consistency across multiple technicians and sites, which is particularly valuable for businesses with a fleet of STIHL MS 291 units.

For field operations, maintain a concise, easily accessible maintenance checklist that accompanies the equipment. The checklist should cover critical items such as chain tension, chain sharpness, lubrication status, fuel levels, air filter condition, and cooling fin cleanliness. If the log indicates a cluster of minor issues, schedule a full workshop maintenance to address them comprehensively, rather than addressing symptoms individually in the field. Align the logbook with the manufacturer’s recommended service intervals and local regulations regarding equipment maintenance and emissions. Over time, the accumulated records become a valuable resource for troubleshooting and performance optimization, helping operators sustain peak efficiency and safety across all cutting tasks.

When preparing service reports for customers or supervisors, include a clear summary of actions taken, parts replaced, and any deviations from standard procedures with justifications. Provide rough estimates of remaining service life for components that show wear, and outline recommended follow-up actions and timing. Maintaining thorough, accurate maintenance records not only supports warranty claims but also enhances resale value and confidence in equipment reliability. By following these guidelines for maintenance scheduling and meticulous record keeping, operators can maximize the STIHL MS 291’s performance while ensuring safety and regulatory compliance on every job.

Appendix and resources

The STIHL MS 291 service manual appendix provides essential references for technicians performing routine maintenance, troubleshooting, and repairs. This section consolidates authoritative contact information, customer support channels, and guidance on accessing official STIHL service documentation. By consulting these resources, technicians can verify part numbers, obtain authorized service procedures, and ensure compliance with STIHL’s engineering standards. It is important to use only STIHL-approved documents and consumables to maintain safety, performance, and warranty integrity for the chainsaw.

The first resource category focuses on Manufacturer contact information. Clear, direct access to STIHL technical support, regional offices, and distributor networks helps technicians procure genuine parts, schedule service, and obtain expert guidance when faced with unusual or non-standard issues. When reaching out, be prepared to provide model details, serial numbers, and a concise description of the symptom or fault. Maintaining a record of these communications can streamline repairs and improve traceability across service events.

The second resource category covers Official STIHL service documentation access. Authorized technicians should reference the latest service bulletins, illustrated parts lists, wiring diagrams, torque specifications, and safety instructions contained in STIHL’s official library. Access to these documents is typically governed by distributor agreements or login credentials, ensuring that only qualified personnel perform advanced procedures. Regularly updating your repository with current documents helps prevent misinterpretation of procedures and promotes consistent, safe maintenance practices for the MS 291.