STIHL MS 251 C Manual

The STIHL MS 251 C is a lightweight, professional-grade chainsaw featuring STIHL's innovative Easy2Start™ system, anti-vibration technology, Ematic™ lubrication system for reduced oil consumption, a side-access chain tensioner, and a quick-stop chain brake. It is designed for demanding cutting tasks such as felling, limbing, and bucking. Below are key sections for safety, features, operation, maintenance, and troubleshooting.

Features at a Glance

Key components: Engine with Easy2Start™, Ematic™ lubrication system, QuickStop® Super chain brake, side-access chain tensioner, anti-vibration system, and STIHL Oilomatic® saw chain.

Feature	Description
Easy2Start™	Reduces pulling force required to start the engine
Ematic™ System	Directs chain oil precisely to reduce consumption
QuickStop® Super	Inertia-activated chain brake for enhanced safety
Side-Access Tensioner	Allows chain adjustment without removing side cover
Anti-Vibration	Reduces operator fatigue during extended use
Decompression Valve	Eases starting by reducing cylinder pressure
Chain Catch	Helps prevent chain from hitting operator if it breaks
Fuel & Oil Caps	Large openings for easy filling
Muffler	Designed for reduced emissions and noise
Handle	Ergonomic design with comfortable grip

Safety Information

Read and understand all safety warnings before operation.

1. Personal Protective Equipment (PPE): Always wear safety glasses, hearing protection, gloves, chainsaw chaps/pants, and sturdy boots.
2. Work Area Safety: Keep bystanders and pets at least 15 feet away. Ensure secure footing and clear escape paths.
3. Chain Brake Test: Test the chain brake function before each use.
4. Kickback Awareness: Be aware of kickback zone (upper quadrant of guide bar tip). Use reduced-kickback chain and maintain sharp chain.

WARNING! A chainsaw is a dangerous tool. Failure to follow safety instructions can result in serious injury or death. Never operate when tired or under the influence.

Assembly & First Use

Unpack and inspect contents. Assemble guide bar and chain.

1. Attach Guide Bar & Chain: Place bar on studs, loop chain over sprocket and onto bar groove, ensuring cutting teeth face forward on top. Install side cover and hand-tighten nuts.
2. Add Fuel & Oil: Use STIHL MotoMix® pre-mixed fuel or mix 50:1 with STIHL HP Ultra oil and 89+ octane gasoline. Fill chain oil reservoir with STIHL chain oil.
3. Tension Chain: Use side-access wheel to adjust tension until chain snaps back when pulled from bottom of bar.
4. Start Engine: Place on ground, engage chain brake, set master control lever to cold start position, pull starter handle until engine fires, then move lever to run position.

CAUTION! Fuel is highly flammable. Refuel in well-ventilated area with engine off and cool. Wipe spills immediately.

Specifications

• Engine Displacement: 45.4 cc
• Power Output: 2.6 kW / 3.5 hp
• Fuel Capacity: 14.2 oz. (0.42 L)
• Oil Capacity: 8.5 oz. (0.25 L)
• Guide Bar Lengths: 16" or 18" (recommended)
• Chain Pitch/Gauge: 3/8" PMM3, .050" (1.3 mm)
• Weight (powerhead): 10.8 lbs (4.9 kg)
• Sound Pressure Level: 106 dB(A)
• Vibration Levels: Front/Rear Handle: 4.5/3.5 m/s²
• Warranty: Limited 1-year commercial, 2-year residential

Controls and Components

Master Control Lever: Combines stop switch, choke, and run positions. Throttle Trigger & Lockout: Prevents accidental throttle engagement. Chain Brake Lever: Manual activation; inertia-activated. Decompression Valve: Button to press before starting. Side-Access Chain Tensioner: Wheel for adjusting chain tension. Fuel & Oil Caps: Marked for easy identification.

Maintenance Points: Air filter cover, spark plug, chain catcher, muffler, anti-vibration elements.

Operation

Starting, cutting techniques, and shutdown.

1. Starting: Engage chain brake. Set master control to cold start. Pull starter handle sharply until engine fires. Move lever to run position. Disengage chain brake before cutting.
2. Basic Cutting: Use full throttle when cutting. Let chain do the work; do not force. Be aware of pinch points, especially when bucking.
3. Felling: Plan escape path. Make notch cut and back cut. Never cut above shoulder height.
4. Shutdown: Allow engine to idle briefly. Move master control to STOP position.

Tip: Keep both hands on handles during operation. Maintain a firm grip with thumb wrapped under handlebar.

Maintenance

Daily and periodic maintenance schedule.

1. Daily: Check chain tension and sharpness. Clean air filter. Check fuel and oil levels. Inspect for loose fasteners.
2. Weekly/Monthly: Clean cooling fins and spark arrestor screen. Check spark plug gap (0.020"). Clean guide bar groove and oil holes.
3. Chain Sharpening: Use correct round file size. Maintain proper filing angle (30°). File all cutters to equal length.
4. Fuel System: Use fresh fuel mix. Empty tank for storage over 30 days.

WARNING! Perform all maintenance with engine off, cool, and spark plug wire disconnected.

Chain & Guide Bar Care

Proper care extends life and improves performance.

Rotate guide bar regularly to ensure even wear. Dress bar rails with a flat file if burred. Clean oil delivery hole in bar. Ensure chain is properly tensioned—should snap back when pulled from underside. Sharpen chain frequently; a sharp chain is safer and more efficient. Use STIHL recommended filing kit.

Storage

Prepare chainsaw for short or long-term storage.

1. Empty fuel tank and run carburetor dry.
2. Remove chain, clean, and soak in oil. Clean guide bar and coat with oil.
3. Clean entire saw, especially cooling fins and air filter.
4. Store in a dry, secure place, out of reach of children.

CAUTION! Never store with fuel in the tank for more than 30 days. Old fuel can damage engine components.

Warranty & Support

STIHL Limited Warranty: 1 year for commercial use, 2 years for non-commercial/residential use from date of retail purchase. Proof of purchase required. Warranty covers defects in material and workmanship. Normal wear, misuse, or improper maintenance are not covered. For genuine parts, service, and support, contact an authorized STIHL servicing dealer. Find a dealer at www.stihlusa.com or call 1-800-467-8445.

Troubleshooting

Symptom	Possible Cause	Corrective Action
Engine will not start	No fuel, flooded, spark plug	Check fuel; set control to run, hold throttle open and pull; check/clean spark plug.
Engine starts then dies	Clogged air/fuel filter, vent	Clean/replace air filter; check fuel tank vent; clean fuel filter.
Loss of power	Dirty air filter, clogged spark arrestor	Clean air filter and spark arrestor screen.
Chain does not turn	Brake engaged, clutch, sprocket	Disengage chain brake; check clutch drum and sprocket for wear.
Excessive chain oil use	Oil adjustment screw	Turn oiler adjustment screw counterclockwise to reduce flow.
Chain throws oil	Over-oiling, wrong oil	Adjust oil flow; use STIHL chain oil.
Vibration increase	Loose fasteners, AV mounts	Tighten all nuts/bolts; inspect anti-vibration elements.

Service: For repairs beyond basic maintenance, take to an authorized STIHL dealer.

Support: 1-800-467-8445; www.stihlusa.com