Stihl MS251C Manual

The Stihl MS251C is a lightweight, professional-grade chainsaw featuring a 45.4 cc engine, STIHL Quickstop® inertia chain brake, Ematic™ lubrication system, decompression valve, and side-access chain tensioner. Designed for demanding cutting tasks with enhanced durability and user safety. Below are key sections for safety, features, operation, maintenance, troubleshooting, and specifications.

Features at a Glance

Key components: 45.4 cc engine, STIHL Quickstop® inertia chain brake, Ematic™ lubrication system, decompression valve, side-access chain tensioner, anti-vibration system, and tool-free air filter cover.

Feature	Description
Engine Displacement	45.4 cc, 2-stroke engine
Guide Bar Length	Typically 16" or 18" (varies by model)
Chain Brake	STIHL Quickstop® inertia-activated
Lubrication System	Ematic™ for reduced oil consumption
Decompression Valve	Easier starting
Chain Tensioning	Side-access, tool-free adjustment
Anti-Vibration System	Reduces operator fatigue
Air Filter	Tool-free cover for easy cleaning
Fuel Tank Capacity	Approx. 14.9 fl oz (0.44 liters)
Oil Tank Capacity	Approx. 8.5 fl oz (0.25 liters)

Safety Information

Read all instructions before operation. Always wear protective gear.

1. Personal Protective Equipment (PPE): Wear safety glasses, hearing protection, gloves, chainsaw chaps, and sturdy boots.
2. Work Area Safety: Clear area of obstacles, ensure secure footing, keep bystanders away.
3. Chain Brake: Test before each use; engage when carrying or not cutting.
4. Kickback Awareness: Avoid contact with bar nose; maintain firm grip.

WARNING! Chainsaws are dangerous; improper use can cause serious injury or death. Never operate when tired or under influence.

Assembly & Preparation

Unpack and inspect contents. Assemble guide bar and chain.

1. Attach Guide Bar: Remove bar cover, fit bar onto studs, align chain with sprocket.
2. Install Chain: Place chain over bar, ensure cutting teeth face forward on top.
3. Tension Chain: Use side adjuster to set proper tension (snug but movable by hand).
4. Fuel Mix: Use 50:1 mix of unleaded gasoline (min. 89 octane) and STIHL 2-cycle oil.
5. Fill Tanks: Add fuel mix to fuel tank; fill bar/chain oil tank with STIHL chain oil.

CAUTION! Use only specified oils; improper mix can damage engine.

Specifications

• Engine: 45.4 cc, single-cylinder 2-stroke.
• Power Output: 2.6 kW (3.5 hp).
• Weight (powerhead): Approx. 10.8 lbs (4.9 kg).
• Fuel Consumption: Approx. 680 g/kWh.
• Sound Pressure Level: 106 dB(A).
• Vibration Levels: Front handle 4.2 m/s², rear handle 3.8 m/s².
• Chain Pitch: 3/8" PMM3.
• Chain Gauge: 0.050" (1.3 mm).
• Ignition System: Electronic, capacitor discharge.
• Warranty: Limited 1-year warranty for personal use.

Controls and Components

Main components: Throttle trigger, throttle trigger lockout, master control lever, chain brake handle, decompression valve, choke knob, fuel cap, oil cap, rear handle, front handle, spark plug, air filter cover.

Master Control Lever: Combines stop switch, choke, and start positions. Chain Brake: Engage by pushing handle forward; disengage by pulling back. Decompression Valve: Press to reduce cylinder pressure for easier starting.

Starting & Stopping

Cold Start Procedure:

1. Engage chain brake.
2. Set master control lever to choke position (full down).
3. Press decompression valve (if equipped).
4. Pump primer bulb 5-6 times (if equipped).
5. Place on ground, hold rear handle with right foot.
6. Pull starter handle until engine fires (1-3 pulls).
7. Move master control to half-throttle position.
8. Pull starter until engine runs.
9. Blip throttle to disengage fast idle.

Stopping: Release throttle, move master control to STOP position.

Operation & Cutting Techniques

Basic Cutting:

1. Disengage chain brake before cutting.
2. Use full throttle when cutting; never "ride" the chain.
3. Let chain do the work; avoid forcing.
4. For felling: Plan escape path, make notch cut, then felling cut.
5. For limbing: Work from trunk outward, support log when possible.
6. For bucking: Support log, cut from top, avoid ground contact.

Kickback Prevention: Hold saw firmly, maintain secure stance, never cut with bar nose.

Maintenance Schedule

Interval	Task
Before each use	Check chain tension, test chain brake, inspect for damage
Daily	Clean air filter, check bar/chain oil flow
Weekly	Clean spark arrestor screen, inspect spark plug
Monthly	Clean cooling fins, check fuel filter
Seasonally	Replace spark plug, clean carburetor air passage
As needed	Sharpen chain, replace worn bar, clean clutch drum

Chain & Bar Care

Chain Sharpening: Use round file matching chain pitch (typically 5/32" or 4.0 mm). Maintain 30° cutting angle, 10° top plate angle. File all cutters equally.

Bar Maintenance: Clean bar groove weekly, flip bar monthly for even wear. Check for "burring" on rails; file if needed.

Lubrication: Always use STIHL chain oil; check oil flow by holding saw over light surface and running at full throttle—oil should appear as line.

Storage Guidelines

Long-term Storage (over 30 days):

1. Drain fuel tank completely.
2. Run engine until it stops to clear carburetor.
3. Remove spark plug, add 1 tsp of engine oil through spark plug hole.
4. Pull starter slowly 2-3 times to distribute oil.
5. Clean entire saw, sharpen chain.
6. Store in dry, cool place, away from ignition sources.

CAUTION! Never store with fuel in tank; fuel can deteriorate and damage engine.

Troubleshooting

Symptom	Possible Cause	Corrective Action
Engine won't start	No spark, flooded, stale fuel	Check spark plug; use fresh 50:1 mix; follow cold start procedure.
Engine runs then dies	Clogged fuel filter, dirty air filter	Replace fuel filter; clean air filter.
Poor cutting performance	Dull chain, improper tension	Sharpen chain; adjust tension.
Chain won't turn	Brake engaged, clutch worn	Disengage chain brake; inspect clutch.
Excessive vibration	Loose components, unbalanced chain	Tighten all fasteners; sharpen chain evenly.
No chain oil	Empty tank, clogged oil passage	Fill oil tank; clean oil holes in bar.

Service: For repairs, contact authorized STIHL dealer. Find dealer at www.stihlusa.com or call 1-800-467-8445.