Stihl MS 251 Manual: A Comprehensive Guide
This guide offers detailed instructions for the Stihl MS 251 chainsaw, covering operation, maintenance, troubleshooting, and parts lists – downloadable as a PDF.
The Stihl MS 251 is a widely-used gasoline-powered chainsaw, known for its reliability and performance in various cutting applications. This manual serves as a comprehensive resource for owners and operators, providing essential information for safe and efficient use. It details everything from initial setup and operation to routine maintenance and troubleshooting common issues.
Users will find detailed parts lists, diagrams, and warranty information within this guide. Whether you’re a professional arborist or a homeowner tackling occasional yard work, understanding your MS 251 is crucial for maximizing its lifespan and ensuring safe operation. Download the PDF for complete details.
Safety Precautions
Operating a chainsaw like the Stihl MS 251 involves inherent risks. Prioritize safety by always wearing appropriate Personal Protective Equipment (PPE), including a helmet, eye protection, hearing protection, gloves, and chainsaw chaps. Before each use, inspect the chainsaw for damage and ensure all safety features are functioning correctly.
Never operate the chainsaw with missing or damaged guards. Maintain a firm grip and secure footing. Be aware of your surroundings and potential hazards like overhead branches or obstructions. Refer to the full manual for detailed safety rules and warnings to prevent serious injury.
Personal Protective Equipment (PPE)
Essential PPE for Stihl MS 251 operation includes a certified helmet with face shield or safety glasses to protect against flying debris. Hearing protection, such as earmuffs, is crucial due to the chainsaw’s loud noise. Heavy-duty, cut-resistant gloves enhance grip and protect hands.
Chainsaw chaps or pants are vital for leg protection, significantly reducing injury risk. Sturdy, non-slip boots provide foot support and protection. Always inspect PPE for damage before each use, ensuring a proper fit for maximum safety during operation.
General Safety Rules
Always read the complete Stihl MS 251 manual before operation, understanding all safety warnings and instructions. Maintain a firm grip with both hands, keeping a safe distance from the chain. Never operate the chainsaw with one hand or while fatigued. Be aware of your surroundings, ensuring no people or obstacles are nearby.
Avoid cutting above shoulder height, maintaining a stable stance. Never force the saw; let the chain do the work. Inspect the saw before each use, checking for loose parts or damage. Always carry the chainsaw with the chain brake engaged.
Understanding the Components
The Stihl MS 251 features a robust engine powering a chain and bar assembly designed for efficient cutting. Key components include the fuel tank, carburetor, air filter, and spark plug, vital for engine function. Familiarize yourself with the location of the chain brake, throttle trigger, and on/off switch.
The chainsaw’s housing protects internal parts, while the anti-vibration system reduces operator fatigue. Understanding these components is crucial for proper maintenance and safe operation, as detailed in the complete manual.
Engine Overview
The Stihl MS 251 is powered by a 2-stroke engine, requiring a fuel-oil mixture for lubrication. Key engine parts include the cylinder, piston, crankshaft, and connecting rod, all working in unison to generate power. The carburetor mixes air and fuel for combustion, while the ignition system initiates the process.
Proper engine maintenance, including air filter cleaning and spark plug replacement, is vital for optimal performance. Refer to the manual for detailed specifications and diagrams of the engine’s internal components.
Chain and Bar Assembly
The Stihl MS 251’s chain and bar are crucial for cutting performance. Proper assembly involves securing the bar to the engine mount, ensuring correct chain tension, and lubricating the chain effectively. Regularly inspect the chain for sharpness and damage, replacing it when necessary.
Bar maintenance includes cleaning the bar groove and checking for wear. Always use a chain specifically designed for the MS 251 to prevent damage and ensure safe operation. Refer to the manual for detailed diagrams and instructions.
Fueling System
The Stihl MS 251 utilizes a two-stroke engine requiring a precise fuel mixture of gasoline and high-quality two-stroke oil. Always use fresh fuel and the correct oil ratio as specified in the operator’s manual – typically 50:1.
The fuel tank features a fuel filter to prevent contaminants from reaching the carburetor. Regularly check and replace the fuel filter to maintain optimal engine performance. Ensure proper fuel cap sealing to avoid spills and fuel evaporation during operation.
Starting the Stihl MS 251
Before each start, perform pre-start checks including fuel level, chain lubrication, and proper assembly. Engage the chain brake for safety. For a cold start, activate the choke control and prime the carburetor bulb several times. Then, firmly grasp the starter handle and pull briskly.
A warm start typically requires no choke; instead, pull the starter cord without engaging the choke. If the engine fails to start after several attempts, consult the troubleshooting section of the manual.
Pre-Start Checks
Prior to starting, always verify sufficient fuel and chain oil levels. Inspect the chain for proper tension and sharpness, ensuring it moves freely around the bar. Confirm the anti-vibration system is intact and functioning correctly. Engage the chain brake for enhanced safety during the starting process.
Additionally, check for any loose parts or damage. Ensure the spark plug cap is securely attached. A thorough pre-start inspection minimizes risks and maximizes operational efficiency.
Cold Start Procedure
For a cold start, engage the chain brake and position the saw on a stable surface. Activate the choke control – typically by sliding it forward. Slowly pull the starter cord with a firm, steady motion until the engine attempts to start. Once it sputters, disengage the choke and continue pulling until the engine runs.
Gradually warm up the engine by allowing it to idle briefly before applying a load. Proper choke usage is crucial for successful cold starts, especially in cooler temperatures.
Warm Start Procedure
When starting a warm engine, the procedure differs slightly. Ensure the chain brake is engaged and the saw is securely positioned. Typically, no choke is required for a warm start; however, if needed, apply it briefly. Pull the starter cord with a smooth, deliberate motion.
The engine should ignite quickly. Avoid excessive pulling, as this can flood the carburetor. Allow the engine to warm up fully before commencing work, ensuring optimal performance and longevity.
Operating Instructions
Before operation, always verify the chain is correctly tensioned and sharpened, and the bar is properly lubricated. Maintain a firm grip with both hands, keeping a safe distance from the chain. When cutting, use proper body positioning and anticipate kickback.
Always be aware of your surroundings and potential hazards. Never operate the saw above shoulder height. Regular checks of chain tension and lubrication are crucial for safe and efficient operation.
Proper Cutting Techniques
Employ a firm stance and secure footing while operating the Stihl MS 251. Utilize the lower portion of the bar for controlled cuts, avoiding pinching. Maintain consistent pressure and let the chain do the work, never forcing it. Be mindful of branch tension during felling to prevent binding.
Always plan your cuts, considering the wood’s weight and potential movement. Avoid cutting with the tip of the bar, as this increases kickback risk. Regular sharpening ensures clean, efficient cuts and reduces strain on the saw.
Felling Trees (Basic Guidelines)
Before felling, assess the tree’s lean, wind direction, and surrounding obstacles. Create a proper notch on the side of the intended fall, typically a 45-degree angle. Follow with a back cut, slightly higher than the notch base, leaving a hinge for control.
Use escape paths angled away from the fall line. Be aware of potential kickback and maintain a safe distance. Never fell trees in hazardous conditions or beyond your skill level; professional assistance is recommended for complex felling operations.
Limbing and Bucking
Limbing involves removing branches from a felled tree, always working from the base towards the tip. Maintain a firm stance and avoid overreaching. Bucking is cutting the trunk into manageable lengths, considering compression and tension forces within the wood.
Support the wood to prevent pinching the chain. Use appropriate cutting techniques for each situation, avoiding cuts that could cause the wood to split or bind the saw. Prioritize safety and maintain control throughout the process.
Maintenance and Servicing
Regular maintenance is crucial for optimal performance and longevity of your Stihl MS 251. This includes frequent chain sharpening to ensure efficient cutting, and consistent bar maintenance – cleaning and checking for wear.
Air filter cleaning prevents engine damage from debris. Fuel system maintenance, like checking the fuel filter, is also vital. Following the schedule outlined in the operator’s manual will help prevent costly repairs and ensure safe operation.
Chain Sharpening
Maintaining a sharp chain is paramount for safe and efficient cutting with your Stihl MS 251; Dull chains require more force, increasing kickback risk and reducing performance. Use a round file of the correct size, guided by a sharpening guide, to restore the cutting angles.
File each tooth consistently, maintaining the correct depth gauges. Regular sharpening extends chain life and ensures clean, precise cuts. Consult the manual for detailed instructions and recommended filing angles for optimal results.
Bar Maintenance
Proper bar maintenance is crucial for smooth chainsaw operation and extended component life. Regularly inspect the guide bar for wear, burrs, and damage. Clean the bar groove to ensure free movement of the chain and optimal lubrication.
Periodically flip the bar to distribute wear evenly. Check the bar rails for straightness and file down any burrs. A well-maintained bar contributes to precise cutting and reduces strain on the engine, enhancing overall performance and safety.
Air Filter Cleaning
Maintaining a clean air filter is vital for optimal engine performance. A dirty filter restricts airflow, leading to reduced power and increased fuel consumption. Regularly inspect the air filter for dirt and debris – ideally after each use, or at least daily with heavy use.
Remove the filter and gently clean it with warm, soapy water. Allow it to dry completely before reinstalling. For heavily soiled filters, consider replacement to ensure consistent engine operation and longevity.
Fuel System Maintenance
Proper fuel system care ensures reliable starting and consistent engine performance. Regularly inspect the fuel lines for cracks or leaks, replacing them as needed. The fuel filter should be checked and replaced periodically to prevent debris from clogging the carburetor.
Carburetor adjustments, specifically high and low settings, may be necessary after cleaning or if performance declines. Refer to the manual for precise adjustment procedures to maintain optimal fuel-air mixture.
Carburetor Adjustment (High & Low)
Adjusting the carburetor requires careful attention to detail. Begin with the engine warmed up. The low-speed screw controls idle and initial acceleration; adjust for smooth running at idle. The high-speed screw governs performance at higher RPMs – adjust for maximum power without engine surging.
Precise settings depend on altitude and fuel mix. Consult the manual for factory specifications and proceed with small adjustments, testing after each change. Incorrect settings can damage the engine.
Fuel Filter Replacement
Regular fuel filter replacement is crucial for optimal engine performance. Locate the filter within the fuel tank, typically accessed by removing the fuel tank cap. Carefully disconnect the fuel line, noting its orientation for reassembly. Remove the old filter and install the new one, ensuring a secure fit.
Prime the fuel system after replacement to remove air pockets. A clogged filter restricts fuel flow, causing starting issues and reduced power. Replace the filter periodically as part of routine maintenance.
Troubleshooting Common Issues
Common problems with the Stihl MS 251 include difficulty starting, stalling, and lack of chain lubrication. If the engine won’t start, check the spark plug, fuel supply, and air filter. Stalling after a few seconds often indicates a dirty carburetor or fuel filter – cleaning is essential.
Insufficient chain lubrication can stem from a blocked oiler or low oil level. Addressing these issues promptly prevents damage and ensures safe operation. Consult the manual for detailed diagnostics.
Engine Won’t Start
If the Stihl MS 251 engine fails to start, several factors could be at play. First, verify the fuel tank contains fresh fuel and the fuel cap vent is clear. Next, inspect the spark plug for fouling or damage – replacement may be necessary. Ensure the choke is engaged correctly for a cold start.
Also, check the air filter for obstructions and confirm the ignition system is functioning. A flooded engine requires specific procedures; consult the manual for details.
Engine Stalls After a Few Seconds
When the Stihl MS 251 engine stalls shortly after starting, a common culprit is a dirty carburetor. Fuel passages can become clogged, restricting fuel flow. Thorough carburetor cleaning is often required, potentially involving disassembly and solvent use.
Additionally, inspect the fuel filter for blockage and ensure proper fuel delivery. A faulty spark plug or a restricted air filter can also contribute to this issue. Check and adjust carburetor settings as needed.
Lack of Chain Lubrication
If the chain isn’t receiving adequate lubrication, friction increases, leading to premature wear and potential damage. First, verify the oil reservoir is full and the oiler cap is securely fastened. Inspect the oil outlet for blockage – debris can obstruct flow.
A malfunctioning oil pump, potentially due to a worn spring or internal damage, is another possibility. Check the pump’s operation and consider replacement if necessary. Ensure the chain brake isn’t engaged, as it can sometimes interfere with oil delivery.
Repairing Common Problems
Addressing issues promptly extends the life of your Stihl MS 251. Spark plug replacement is straightforward – disconnect the boot, remove the old plug, gap the new one correctly, and reinstall. For a clogged carburetor, disassembly and cleaning with carburetor cleaner are essential.
Pay close attention to small parts during reassembly. If issues persist after these repairs, professional servicing is recommended. Always use genuine Stihl replacement parts to maintain performance and safety.
Spark Plug Replacement
To replace the spark plug, first ensure the engine is cool and disconnected from the spark plug wire. Carefully remove the wire boot, then use a spark plug socket to unscrew the old plug. Inspect the new plug and adjust the gap to the manufacturer’s specification – typically 0.08 inches.
Thread the new plug in by hand to avoid cross-threading, then tighten with the socket. Reattach the spark plug wire securely. A faulty spark plug can cause starting difficulties or poor engine performance.
Gaźnik Cleaning
A clogged carburetor is a common cause of starting issues and poor engine running. Begin by disconnecting the fuel line and carefully disassembling the carburetor. Use carburetor cleaner to thoroughly spray and clean all jets, passages, and the float chamber. Pay close attention to small orifices, ensuring they are clear.
Reassemble the carburetor with new gaskets if necessary. Incorrect carburetor adjustment or a dirty carburetor can lead to stalling after a few seconds of operation, as reported by some users.
Technical Specifications
The Stihl MS 251 is a gasoline-powered chainsaw designed for various cutting tasks. Engine displacement is 45.4 cc (2.77 cu in), delivering a power output of 2.2 kW (3.0 hp). Its weight, excluding the bar and chain, is approximately 5.8 kg (12.8 lbs). The fuel tank capacity is 0.25 liters (8.5 fl oz), while the oil tank holds 0.21 liters (7.1 fl oz).
Dimensions vary slightly depending on the bar length installed, but generally, it’s a compact and manageable tool for professional and home users alike.
Engine Data
The Stihl MS 251 utilizes a 2-stroke engine with displacement of 45.4 cc (2.77 cubic inches). Its cylinder bore measures 40 mm (1.57 in), and the piston stroke is 32 mm (1.26 in). The compression ratio is 12:1, requiring a minimum octane rating of 90 RON/87 AKI gasoline mixed with a high-quality 2-stroke engine oil. Maximum engine speed reaches 9,000 rpm, providing ample power for diverse cutting applications;
Ignition is CDI (Capacitive Discharge Ignition) for reliable starting.
Weight and Dimensions
The Stihl MS 251 boasts a dry weight of approximately 5.8 kg (12.8 lbs), contributing to its maneuverability. Overall length measures 39.6 cm (15.6 in), providing a balanced reach for various cutting tasks. The bar length options range from 30 cm (12 in) to 45 cm (18 in), adapting to different job requirements. Its height is around 26.8 cm (10.6 in), and width is 24.3 cm (9.6 in), ensuring compact storage.
These dimensions enhance user control and efficiency.
Parts List and Diagrams
Detailed parts lists for the Stihl MS 251 are crucial for repairs and maintenance, identifying each component with a unique part number. Exploded view diagrams visually represent how these parts assemble, simplifying the repair process. These resources, often spanning multiple pages (up to 39 pages in some manuals), cover everything from the engine to the chain and bar assembly.
Accessing these diagrams, often in PDF format, ensures accurate part identification and successful servicing of your chainsaw.
Warranty Information
Stihl products, including the MS 251 chainsaw, are backed by a limited warranty against defects in materials and workmanship. Warranty duration varies depending on the intended use – commercial or residential. Registration of your Stihl MS 251 is often required to validate warranty coverage.
The official Stihl warranty statement, found within the operator’s manual or on the Stihl website, details specific terms, conditions, and exclusions. Proper maintenance, as outlined in the manual, is essential to maintain warranty validity.
Disposal Considerations
Responsible disposal of your Stihl MS 251 chainsaw is crucial for environmental protection. Do not simply discard the unit with regular waste. Old engines contain potentially hazardous components like oil and fuel requiring careful handling.
Contact your local Stihl dealer or waste management facility for information on proper recycling or disposal procedures. Many communities offer designated collection points for electronic and gasoline-powered equipment. Adhering to local regulations ensures environmentally sound practices.
