Stihl MS 251 C-BE Manual

The Stihl MS 251 C-BE is a professional-grade chainsaw featuring a powerful 45.4 cc engine with STIHL 2-MIX technology for reduced emissions and fuel consumption, an anti-vibration system, QuickStop® inertia chain brake, Ematic™ lubrication system, side-access chain tensioner, tool-free air filter cover, and Easy2Start™ system. Below are key sections for safety, features, operation, maintenance, and troubleshooting.

Features at a Glance

Key components: Engine with STIHL 2-MIX technology, anti-vibration system, QuickStop® chain brake, Ematic™ lubrication, side-access chain tensioner, tool-free air filter cover, and Easy2Start™ system.

Feature	Description
Engine	45.4 cc STIHL 2-MIX engine for high power with low emissions
Anti-Vibration System	Reduces operator fatigue during extended use
QuickStop® Inertia Chain Brake	Automatically stops chain in kickback situations
Ematic™ Lubrication System	Directs oil precisely to chain and bar for reduced consumption
Side-Access Chain Tensioner	Allows easy chain adjustment from the side
Tool-Free Air Filter Cover	Quick access for cleaning without tools
Easy2Start™ System	Reduces pulling force required for starting
Fuel Tank Capacity	0.53 US pt (0.25 l)
Oil Tank Capacity	0.32 US pt (0.15 l)
Recommended Bar Lengths	16" or 18" (Guide bar 3005 000 4820/4821)

Safety Information

Read all instructions before operation. Wear appropriate PPE: safety glasses, hearing protection, gloves, chainsaw chaps, and sturdy boots.

1. Inspect chainsaw before each use: check chain tension, sharpness, and lubrication.
2. Clear work area of obstacles and ensure secure footing.
3. Never operate with one hand; always use both hands on handles.
4. Be aware of kickback zone; do not let bar nose contact objects.
5. Shut off engine before adjusting, transporting, or leaving unattended.

WARNING! Chainsaw kickback can cause severe injury. Always engage chain brake when not cutting. Keep bystanders at a safe distance.

Assembly & Preparation

Unpack and inspect contents. Assemble guide bar and chain.

1. Attach guide bar: Place bar onto studs, align chain with sprocket, tension chain.
2. Fill fuel: Use STIHL MotoMix® or 50:1 mixture of gasoline and STIHL HP Ultra oil.
3. Fill chain oil: Use STIHL chain oil or equivalent.
4. Check controls: Ensure throttle trigger, throttle trigger lockout, and master control lever function properly.

CAUTION! Use only STIHL-approved fuels and lubricants. Do not use automotive oil or mixed fuels older than 30 days.

Specifications

• Engine Displacement: 45.4 cc.
• Power Output: 2.6 kW (3.5 bhp).
• Fuel/Oil Ratio: 50:1 (STIHL MotoMix® recommended).
• Weight (Powerhead): 10.8 lbs (4.9 kg).
• Sound Pressure Level: 106 dB(A).
• Vibration Level (Front/Rear): 4.5/2.5 m/s².
• Chain Pitch/Gauge: 3/8" P / .050" (1.3 mm).
• Ignition System: Electronic, capacitor discharge.
• Warranty: Limited 1-year commercial, 2-year residential.

Controls and Components

Master Control Lever: Combines stop switch, choke, and fast idle. Front Handle: Includes throttle trigger lockout. Rear Handle: Contains throttle trigger. Right Side: Chain brake lever, side-access chain tensioner.

Additional Controls: Decompression valve (for easier starting), purge bulb (primes carburetor), fuel/oil caps, air filter cover latch.

Maintenance: Chain tension adjustment, air filter cleaning, spark plug access, muffler cover removal.

Starting & Stopping

Starting (Cold Engine):

1. Engage chain brake by pushing forward.
2. Set master control lever to choke position (✱).
3. Press purge bulb 5-6 times until fuel visible.
4. Place on ground, hold rear handle with right foot.
5. Pull starter handle until engine fires (1-2 pulls).
6. Move master control to half-throttle position (⏻).
7. Pull starter to start; engine will run at fast idle.
8. Blip throttle to return to idle.

Stopping: Release throttle, move master control to STOP (0).

Tip: For warm restart, set master control to run position (⏼) only.

Operation Guidelines

Proper cutting techniques ensure safety and efficiency.

1. Felling: Plan escape path. Make notch cut, then felling cut. Use wedges if needed.
2. Limbing: Work from trunk outward. Keep saw stable; avoid tip contact.
3. Bucking: Support log fully. Cut from top, avoid ground contact.
4. Kickback Prevention: Hold firmly, do not overreach, maintain sharp chain.
5. Chain Lubrication: Check oil flow by running saw over light surface; look for oil line.

WARNING! Do not cut above shoulder height. Watch for tension in wood to prevent pinching.

Maintenance Schedule

Daily: Clean air filter, check chain tension/sharpness, inspect for loose parts. Weekly: Clean cooling fins, check spark plug, clean guide bar groove. Monthly: Clean fuel filter, replace air filter if damaged, inspect anti-vibration elements.

CAUTION! Disconnect spark plug wire before performing maintenance. Use only STIHL replacement parts.

Chain & Bar Care

Sharpening: Use round file (7/32" or 5.5 mm) with guide. Maintain 30° cutting angle, 10° top plate angle. Depth gauges: File to 0.025" (0.65 mm) with depth gauge tool.

Bar Maintenance: Clean groove weekly, flip bar monthly for even wear, file rails if burred.

Tip: Keep chain sharp; dull chains increase kickback risk and reduce efficiency.

Storage

Long-term storage: Empty fuel tank, run engine dry. Remove chain, clean and oil. Store in dry place, cover to prevent dust.

CAUTION! Never store with fuel in tank for more than 30 days. Fuel deterioration can damage carburetor.

Troubleshooting

Symptom	Possible Cause	Corrective Action
Engine won't start	Fuel, spark, air	Check fuel freshness, spark plug, air filter. Use fresh 50:1 mix.
Engine runs poorly	Clogged filter/carburetor	Clean/replace air filter; have carburetor serviced.
Chain doesn't turn	Brake engaged/low oil	Disengage chain brake; check oil level and flow.
Excessive vibration	Loose parts/damaged AV	Tighten all fasteners; inspect anti-vibration mounts.
Chain throws oil	Over-oiling	Adjust oil flow via screw (if equipped); use correct oil.
Chain dulls quickly	Cutting dirty wood	Avoid ground contact; sharpen regularly.

Service: For repairs, contact authorized STIHL dealer. Do not attempt major repairs yourself.

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