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, decompression valve for easy starting, side-access chain tensioner, and an Ematic™ lubrication system. It is designed for demanding cutting tasks such as 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, master control lever, chain brake, anti-vibration system, and fuel/oil tanks.

Assembly & Preparation

Unpack and inspect all contents. Assemble on a clean, stable surface.

1. Attach the guide bar and chain: Place bar on studs, fit chain over sprocket and bar, adjust tension.
2. Fill with fuel: Use STIHL MotoMix® or mix high-quality 2-stroke oil (50:1 ratio) with unleaded gasoline (min. 89 octane).
3. Fill chain oil: Use STIHL chain oil or a quality substitute.
4. Check chain brake: Ensure it engages and disengages properly.

WARNING! Always wear appropriate personal protective equipment (PPE): helmet, eye protection, hearing protection, gloves, and chainsaw chaps.

First-Time Operation

Perform pre-start checks before each use.

1. Check chain tension: Chain should be snug against bar but pull freely.
2. Check chain sharpness: A sharp chain reduces kickback risk and improves cutting.
3. Start the saw: Place on ground, engage chain brake, set master control to cold start position, pull starter rope until engine fires, then set to run position and start.
4. Warm up: Allow engine to idle for 30 seconds before cutting.

CAUTION! Never start the saw unless the chain brake is engaged and you are in a clear, stable position.

Specifications

• Engine Power: 4.0 bhp (3.0 kW).
• Powerhead Weight: Approx. 13.9 lbs (6.3 kg) without bar and chain.
• Fuel/Oil Ratio: 50:1 (STIHL 2-stroke oil).
• Ignition System: STIHL Electronic Ignition (EM).
• Chain Pitch/Gauge: Typically 3/8" or .325", 0.063" gauge (check bar marking).
• Sound Power Level: Approx. 112 dB(A).
• Vibration Levels: Left/Right: 4.5 m/s², Front/Rear: 2.5 m/s².
• Warranty: Limited warranty for personal/commercial use (see manual).

Controls and Functions

Master Control Lever: Combines stop (0), run (I), and start/choke positions. Throttle Trigger: Controls engine speed. Throttle Trigger Interlock: Must be depressed to engage throttle. Chain Brake Lever: Manual activation; also inertia-activated. Decompression Valve: Button to press before starting. Chain Catcher: Helps reduce risk if chain breaks. Front Hand Guard: Protects left hand.

Maintenance Controls: Side-access chain tensioner, oil filler caps, air filter cover, spark plug access.

Safe Operation Procedures

Always plan your cut, maintain secure footing, and be aware of your surroundings.

1. Starting: Follow starting procedure exactly; never "drop start".
2. Cutting: Use full throttle when cutting; let chain do the work.
3. Kickback Prevention: Keep saw body close to your body; do not cut with the tip of the bar.
4. Carrying: Engage chain brake when moving more than a few steps.
5. Shut Down: Allow to idle briefly, then move master control to STOP (0).

Tip: Regularly check chain brake function by performing a manual test (see manual).

Maintenance Schedule

Daily or before each use: Check chain tension and sharpness, check fuel and oil levels, inspect for loose parts or damage.

1. Air Filter: Clean regularly; replace if damaged.
2. Spark Plug: Clean and check gap (0.020") every 10 hours; replace as needed.
3. Fuel Filter: Replace annually or if clogged.
4. Chain Sprocket: Inspect for wear; replace if worn (can cause chain damage).
5. Bar: Clean bar groove and oil holes; flip bar regularly for even wear.
6. Anti-Vibration Elements: Inspect for wear or damage.

WARNING! Perform maintenance only when the saw is switched off and completely cool. Disconnect the spark plug boot for safety.

Chain & Bar Care

Proper chain tension is critical. A loose chain can derail; an overtightened chain can damage the bar and sprocket.

Sharpening: Use correct round file size for your chain pitch. Maintain correct filing angle (typically 30°). File all cutters to equal length. Depth gauges must be filed down periodically.

Storage Guidelines

For long-term storage (over 30 days):

1. Drain fuel tank and run engine until it stops to clear carburetor.
2. Remove chain, clean it and the bar, and coat with oil.
3. Clean entire saw and store in a dry, dust-free place.
4. Protect from extreme temperatures.

CAUTION! Never store a chainsaw with fuel in the tank for extended periods. Old fuel can damage engine components.

Regulatory & Warranty Information

This chainsaw meets applicable ANSI/OPEI standards. It is EPA and CARB certified for emissions. STIHL, the STIHL logo, and Quickstop are trademarks of ANDREAS STIHL AG & Co. KG. The warranty is valid only when the product is purchased from an authorized STIHL dealer. For technical support, parts, or service, contact your local authorized STILL dealer or visit www.stihlusa.com.

Troubleshooting

Service: For repairs beyond basic maintenance, contact an authorized STIHL servicing dealer.

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