STIHL MS 291 Chainsaw Manual

The STIHL MS 291 is a professional-grade chainsaw featuring a powerful 55.5cc engine, STIHL Quickstop® inertia chain brake, Ematic™ lubrication system, anti-vibration system, decompression valve for easy starting, side-access chain tensioner, and STIHL ErgoStart™. This manual covers safety, features, assembly, operation, maintenance, and troubleshooting. Always read and understand the manual before use.

1. Features at a Glance 2. Assembly & Preparation 3. First-Time Operation 4. Specifications 5. Controls and Functions 6. Chain & Bar Setup 7. Operation Procedures 8. Safety Features 9. Maintenance & Cleaning 10. Regulatory Information 11. Troubleshooting

Features at a Glance

Key components: Engine, guide bar, saw chain, chain brake, throttle trigger, master control lever, fuel tank, oil tank, and anti-vibration system.

Feature	Description
Engine Displacement	55.5 cc two-stroke engine
Guide Bar Length	Typically 16" to 20" (options available)
Chain Brake	STIHL Quickstop® inertia-activated
Lubrication System	Ematic™ for reduced oil consumption
Starting System	ErgoStart™ and decompression valve
Anti-Vibration	Reduced vibration handles
Chain Tensioning	Side-access for easy adjustment
Fuel Tank Capacity	Approx. 16.9 fl oz (500 ml)
Oil Tank Capacity	Approx. 11.8 fl oz (350 ml)
Weight (powerhead)	Approx. 12.8 lbs (5.8 kg)

Assembly & Preparation

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

Attach guide bar and chain: Place bar on studs, fit chain with drive links in bar groove, tension correctly.
Fill fuel: Use STIHL MotoMix® or mix 50:1 with STIHL HP Ultra oil and unleaded gasoline (min. 89 octane).
Fill chain oil: Use STIHL chain oil or approved substitute.
Check controls: Ensure throttle trigger, chain brake, and master control lever function properly.

WARNING! Chainsaw is dangerous; wear protective gear (helmet, gloves, chaps, boots, eye/ear protection). Keep bystanders away.

First-Time Operation

Before starting, ensure chain brake is engaged (pulled forward).

Cold start: Set master control to choke position (full down), press decompression valve, pull starter rope until engine fires, move control to half-throttle, pull again to start.
Warm start: Set master control to run position, pull starter.
Disengage chain brake: Pull back toward handle.
Test chain: Hold saw firmly, briefly apply throttle to check chain rotation and oiling.

CAUTION! Never drop-start or start above waist height. Keep firm grip with both hands.

Specifications

Engine: 55.5 cc single-cylinder two-stroke.
Power Output: 3.4 kW (4.6 bhp).
Fuel/Oil Mix: 50:1 (STIHL HP Ultra).
Chain Pitch/Gauge: .325" / .063" (typical).
Sound Pressure: Approx. 106 dB(A).
Vibration (front/rear): Approx. 4.5/2.5 m/s².
Ignition: Electronic, capacitor discharge.
Carburetor: Diaphragm-type with fuel pump.
Warranty: Limited warranty; see STIHL terms.

Controls and Functions

Master Control Lever: Combines stop switch, choke, and run positions. Throttle Trigger: Controls engine speed. Throttle Trigger Lockout: Must be depressed to access throttle. Chain Brake Handle: Engages brake when pushed forward; protects against kickback. Decompression Valve: Reduces cylinder pressure for easier starting. Side-Access Chain Tensioner: Adjusts chain tension without tools.

Maintenance Controls: Air filter cover, spark plug access, fuel/oil caps, chain catcher, and muffler.

Chain & Bar Setup

Proper chain tension is critical: Chain should snap back when pulled from bar.

Loosen bar nuts with combination wrench.
Turn tensioning screw clockwise to tighten chain; check fit.
Retighten bar nuts while lifting bar tip.
Check oil flow: Run saw at high idle; look for oil line on ground.

Tip: Always use matched STIHL guide bar, chain, and sprocket. Keep chain sharp.

Operation Procedures

Supports felling, limbing, bucking, and pruning.

Starting: Follow cold/warm start procedure.
Cutting: Use full throttle in cut; let chain do the work.
Kickback avoidance: Hold firmly, avoid tip contact, use reduced-kickback chain.
Stopping: Release throttle, engage chain brake, move master control to STOP.
Refueling: Stop engine, let cool, clean area, use fuel can with spout.

WARNING! Beware of kickback—can cause severe injury. Never operate above shoulder height or with one hand.

Safety Features

Chain Brake: Automatically engages on kickback or manually activated. Throttle Trigger Lockout: Prevents accidental throttle engagement. Right-Hand Guard: Protects from chain breakage. Chain Catcher: Helps catch broken chain. Anti-Vibration System: Reduces operator fatigue. Muffler: Reduces noise and directs exhaust.

Maintenance & Cleaning

Perform daily checks: Chain sharpness, tension, bar condition, air filter, fuel/oil levels.

Weekly: Clean cooling fins, check spark plug, clean chain brake mechanism.

Monthly: Inspect fuel lines, carburetor adjustment (by dealer if needed), sprocket wear.

CAUTION! Always disconnect spark plug before maintenance. Use STIHL parts only.

Regulatory Information

EPA and CARB compliant for emissions. Meets ANSI B175.1 safety standards. Copyright © STIHL Incorporated. STIHL, Quickstop, Ematic, and ErgoStart are trademarks. For support, visit www.stihlusa.com or contact 1-800-467-8445.

Troubleshooting

Symptom	Possible Cause	Corrective Action
Engine won't start	Fuel, spark, flood	Check fuel mix; clean spark plug; wait if flooded; ensure choke correct.
Engine runs poorly	Air filter, carburetor	Clean/replace air filter; have dealer adjust carburetor.
Chain doesn't oil	Oil tank, passages	Fill oil; check oiler holes; clean bar groove; replace oil pump if needed.
Chain comes off bar	Tension, wear	Adjust tension; check bar wear; replace if grooved.
Excessive vibration	Balance, mounting	Check bar/chain match; ensure all fasteners tight.

Service: Authorized STIHL dealers only. Do not attempt major repairs yourself.

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