STIHL MS 251 C Manual

The STIHL MS 251 C is a lightweight, professional-grade chainsaw featuring a powerful 45.4 cc engine with STIHL's innovative Easy2Start™ system, anti-vibration technology, Ematic™ lubrication system, QuickStop® Plus inertia chain brake, side-access chain tensioner, and a decompression valve for easier starting. Below are key sections for safety, features, operation, maintenance, and troubleshooting.

Features at a Glance

Key components: Engine with Easy2Start™, anti-vibration system, QuickStop® Plus chain brake, side-access chain tensioner, Ematic™ lubrication, and decompression valve.

Feature	Description
Easy2Start™	Reduces starting resistance by up to 30%
QuickStop® Plus	Inertia-activated chain brake for enhanced safety
Ematic™ Lubrication	Directs oil precisely to the chain for reduced consumption
Anti-Vibration System	Reduces operator fatigue during extended use
Side-Access Chain Tensioner	Allows easy chain adjustment without removing cover
Decompression Valve	Reduces cylinder pressure for easier pull starts
Chain Catcher	Helps reduce risk if chain breaks or derails
Throttle Interlock	Prevents accidental throttle activation
Master Control Lever	Combines choke, throttle, and stop functions
Fuel & Oil Caps	Large openings for easy filling

Safety Information

Read all instructions before operation. Wear proper PPE.

1. Personal Protective Equipment (PPE): Wear safety glasses, hearing protection, gloves, chainsaw chaps, and steel-toe boots.
2. Work Area Safety: Clear area of bystanders, especially children. Ensure secure footing.
3. Kickback Zone: Avoid contact with upper quadrant of guide bar tip.
4. Fuel Safety: Refuel in well-ventilated area, away from ignition sources. Use STIHL MotoMix® or 89+ octane fuel with STIHL HP Ultra oil.

WARNING! Kickback can cause severe injury. Always hold saw firmly with both hands.

Assembly & First Use

Assemble guide bar and chain. Fill with fuel and oil.

1. Attach Guide Bar & Chain: Place bar on studs, loop chain over sprocket, tension correctly.
2. Fill Fuel Tank: Use fresh fuel mix (50:1 with STIHL HP Ultra). Do not overfill.
3. Fill Oil Tank: Use STIHL chainsaw bar oil. Check flow before cutting.
4. Starting Procedure: Engage chain brake. Set Master Control to cold start position. Pull starter handle until engine fires, then move lever to run position and restart.

CAUTION! Ensure chain brake is engaged before starting. Keep hands away from cutting area.

Specifications

• Engine Displacement: 45.4 cc
• Power Output: 2.6 kW / 3.5 HP
• Fuel Capacity: 0.5 L (16.9 fl. oz.)
• Oil Capacity: 0.26 L (8.8 fl. oz.)
• Guide Bar Lengths: 16" or 18" (recommended)
• Chain Pitch/Gauge: 3/8" PMM / 0.050"
• Weight (powerhead): 5.2 kg (11.5 lbs)
• Sound Pressure Level: 106 dB(A)
• Vibration Levels: Left/Right 3.2 m/s², Front/Rear 2.8 m/s²

Controls and Components

Master Control Lever: Combines stop switch, choke, and throttle functions. Front Handle: Includes throttle trigger and throttle interlock. Rear Handle: Contains Master Control Lever and starter grip.

Safety Features: QuickStop® Plus chain brake (manual or inertial activation), chain catcher, right-hand guard, throttle interlock.

Maintenance Points: Side-access chain tensioner, spark plug, air filter, fuel and oil caps, chain lubrication adjustment.

Operation

Starting, cutting techniques, and shutdown.

1. Starting: Engage chain brake. Set Master Control to cold start. Pull starter until engine fires, then move to run position and restart.
2. Cutting: Use full throttle when cutting. Let chain do the work; do not force.
3. Kickback Prevention: Hold saw firmly, avoid tip contact, maintain secure stance.
4. Shutdown: Move Master Control to stop position. Engage chain brake when not in use.

Tip: Regularly check chain tension and lubrication during operation.

Maintenance & Cleaning

Daily and periodic maintenance schedule.

1. Air Filter: Clean regularly; replace if damaged.
2. Spark Plug: Check gap (0.5 mm / 0.020"); replace if worn.
3. Fuel Filter: Replace annually or if clogged.
4. Chain Sprocket: Inspect for wear; replace if necessary.
5. Exterior Cleaning: Remove debris from cooling fins, air intake, and guide bar groove.

WARNING! Perform maintenance only when engine is off and cool. Disconnect spark plug boot.

Chain & Bar Care

Sharpening, tensioning, and bar maintenance.

1. Sharpening: Use round file and guide. Maintain correct filing angle (30°).
2. Tensioning: Adjust via side-access when chain is cool. Proper tension = snug against bar but pullable by hand.
3. Bar Maintenance: Clean groove regularly, flip bar periodically for even wear.
4. Lubrication: Ensure oiler is working; adjust flow if needed.

CAUTION! A dull chain increases kickback risk and reduces efficiency.

Storage

Long-term and short-term storage procedures.

1. Short-term: Clean saw, empty fuel tank, or add fuel stabilizer.
2. Long-term: Run engine dry, remove spark plug, add oil to cylinder, store in dry place.
3. Chain: Remove, clean, and soak in oil.

CAUTION! Never store with fuel in tank for more than 30 days without stabilizer.

Regulatory Information

EPA and CARB compliant. Meets ANSI B175.1 safety standards. Manufactured by STIHL Incorporated. For genuine parts and service, contact authorized STIHL dealers. For support, visit www.stihlusa.com or call 1-800-467-8445.

Troubleshooting

Symptom	Possible Cause	Corrective Action
Engine won't start	Fuel, spark, or air	Check fuel mix, spark plug, air filter. Use fresh fuel.
Engine runs poorly	Clogged filter or carb	Clean/replace air filter. Check fuel filter and carburetor.
Chain doesn't turn	Brake engaged or clutch	Disengage chain brake. Check clutch and sprocket.
Excessive vibration	Loose components or chain	Tighten all fasteners. Check chain balance and sharpness.
Chain throws oil	Over-lubrication	Adjust oiler flow. Use correct oil viscosity.
Chain dulls quickly	Cutting dirty wood or improper filing	Avoid cutting into dirt. Sharpen correctly with proper file size.

Service: For repairs, use authorized STIHL dealers only.

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