Stihl Chainsaw MS 391 Manual

The STIHL MS 391 is a professional-grade chainsaw featuring a powerful 64.1 cc engine, STIHL Quickstop® inertia chain brake, anti-vibration system, Ematic™ lubrication, side-access chain tensioner, and a decompression valve for easier starting. It is designed for demanding cutting tasks, including felling, limbing, and bucking. Below are key sections for safety, features, assembly, operation, maintenance, and troubleshooting.

Features at a Glance

Key components: Engine, guide bar, saw chain, chain brake, throttle trigger, master control lever, fuel and oil tanks.

Safety Information

Read and understand all instructions before use. Always wear proper PPE.

1. Personal Protective Equipment (PPE): Wear safety glasses, hearing protection, gloves, chainsaw chaps/pants, and sturdy boots.
2. Work Area Safety: Clear area of obstacles, ensure secure footing, keep bystanders away.
3. Chain Brake: Test function before each use. Engage when carrying or not cutting.
4. Kickback: Be aware of kickback zone (upper quadrant of bar tip). Hold saw firmly.

WARNING! Improper use can cause serious injury or death. Never operate when tired or under the influence.

Assembly & Preparation

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

1. Attach Guide Bar & Chain: Place bar on studs, loop chain over sprocket and bar, adjust tension.
2. Fuel Mix: Use high-quality 2-stroke engine oil mixed with unleaded gasoline (50:1 ratio for STIHL oil).
3. Fill Fuel Tank: Use clean fuel mix. Do not overfill.
4. Fill Chain Oil Tank: Use STIHL chain oil or equivalent for lubrication.
5. Check Chain Tension: Chain should snap back when pulled from bar.

CAUTION! Fuel is flammable. Fill in well-ventilated area, away from ignition sources.

Specifications

• Engine Displacement: 64.1 cc.
• Powerhead Weight: Approx. 13.9 lbs (6.3 kg) without bar and chain.
• Guide Bar Lengths: Typically 16" to 25" (available options).
• Chain Pitch/Gauge: 3/8" PM / .050" (standard).
• Fuel/Oil Ratio: 50:1 with STIHL 2-stroke oil.
• Sound Power Level: Meets applicable standards (check local regulations).
• Vibration Levels: Reduced via anti-vibration system.
• Warranty: Limited warranty; see dealer for details.

Controls and Components

Familiarize yourself with all controls before operation.

Main Controls: Master Control Lever (Choke/Start/Run/Stop), Throttle Trigger, Throttle Trigger Lockout, Chain Brake Lever, Decompression Valve, Fuel/Oil Caps.

Components: Muffler, Spark Plug, Air Filter, Chain Catcher, Front & Rear Hand Guards, Spark Arrestor Screen (if equipped).

Operation: Master control lever settings: Stop (0), Run (I), Choke/Start (II). Chain brake: Push forward to engage (brake on), pull back to disengage (brake off).

Starting & Stopping

Follow correct procedure to avoid damage and ensure safety.

1. Cold Start: Engage chain brake. Set master control to choke (II). Press decompression valve. Pull starter rope until engine fires. Move lever to run (I). Pull to start.
2. Warm Start: Master control to run (I). Pull starter rope.
3. Stopping: Release throttle. Move master control to stop (0).

Tip: Always engage chain brake when starting or carrying the saw.

Operating Instructions

Use proper cutting techniques for efficiency and safety.

1. Felling: Plan escape path. Make notch cut, then felling cut. Use wedges if needed.
2. Limbing: Stand on opposite side of log. Cut from top, avoid tip contact.
3. Bucking: Support log. Use undercut for binding. Let chain do the work.
4. General: Operate at full throttle when cutting. Avoid cutting with bar tip.
5. Kickback Prevention: Maintain firm grip, be aware of tip position, use reduced-kickback chain.

WARNING! Never operate above shoulder height or with one hand. Beware of reactive forces.

Maintenance Schedule

Regular maintenance ensures performance and longevity.

Note: Use only STIHL-approved parts and lubricants.

Chain Sharpening & Tensioning

A sharp, properly tensioned chain is essential.

1. Sharpening: Use correct round file size (typically 5/32" for 3/8" PM chain). Maintain 30° filing angle. File all cutters evenly.
2. Tensioning: Loosen bar nuts. Adjust tensioning screw until chain fits snug against bar bottom. Tighten bar nuts. Re-check tension.
3. Depth Gauges: File depth gauges with flat file to maintain proper height (use gauge tool).

CAUTION! Wear gloves. Chain is sharp. Ensure saw is off and cool.

Storage

Prepare saw for storage to prevent fuel system issues.

1. Short Term: Run carburetor dry or add fuel stabilizer.
2. Long Term: Drain fuel and oil tanks completely. Clean entire saw. Remove chain and store in oil.
3. Location: Store in dry, secure place, out of reach of children.

CAUTION! Never store with fuel in tank for extended periods without stabilizer.

Troubleshooting

Service: For major repairs, contact an authorized STIHL servicing dealer.

Support: STIHL Inc., 1-800-467-8445, www.stihlusa.com