stihl ms 250 workshop manual

The STIHL MS 250 is a professional-grade chainsaw featuring a powerful 45.4 cc engine, STIHL Quickstop® inertia chain brake, Ematic™ lubrication system, anti-vibration system, side-access chain tensioner, and a decompression valve for easy starting. This workshop manual provides detailed instructions for maintenance, repair, troubleshooting, and safety procedures. Below are key sections covering specifications, safety, maintenance intervals, engine service, fuel system, ignition, cutting equipment, and troubleshooting.

Specifications & Technical Data

Key technical specifications for the STIHL MS 250 chainsaw.

Feature	Specification
Engine Displacement	45.4 cc
Power Output	2.6 kW (3.5 bhp)
Fuel Tank Capacity	0.50 L
Oil Tank Capacity	0.26 L
Guide Bar Length (Recommended)	40 cm (16") / 45 cm (18")
Chain Pitch / Gauge	3/8" PM / 1.5 mm
Weight (Powerhead only)	5.0 kg
Ignition System	Electronic, capacitor discharge (CDI)
Carburetor	Zama C1Q-S199 / Walbro WT-215
Spark Plug	NGK BPMR7A (gap 0.5 mm)

Safety Information & Warnings

Critical safety procedures must be followed before any service work.

1. Disconnect Spark Plug: Always remove the spark plug boot before performing any maintenance.
2. Fuel Safety: Drain fuel tank in a well-ventilated area away from sparks or flames.
3. Chain Brake Check: Verify Quickstop® inertia brake function before and after service.
4. Personal Protective Equipment (PPE): Wear safety glasses, gloves, and hearing protection.
5. Work Area: Ensure clean, organized, and well-lit workspace.

WARNING! Failure to follow safety instructions can result in serious injury or death. The chain can kick back even when the engine is off.

Maintenance Schedule & Intervals

Recommended service intervals for optimal performance and longevity.

1. Daily/Before Use: Check chain tension, sharpness, and lubrication. Inspect for loose fasteners.
2. Every 10 Hours: Clean air filter, check spark plug condition, clean cooling fins.
3. Every 20 Hours: Replace fuel filter, clean spark arrestor screen (if equipped).
4. Every 50 Hours: Clean carburetor air passage, check fuel lines for cracks, replace spark plug.
5. Every 100 Hours: Check piston/cylinder through exhaust port, clean muffler, inspect clutch and sprocket.
6. Seasonal/Storage: Drain fuel system or use stabilizer. Clean entire saw and store in dry place.

CAUTION! Use only genuine STIHL replacement parts and specified lubricants.

Engine Disassembly & Assembly

Step-by-step procedure for engine top-end service.

• Tools Required: STIHL tool kit, torque wrench, piston stop, ring compressor, gasket set.
• Disassembly: Remove muffler, cylinder cover, decompression valve, cylinder bolts. Lift cylinder off carefully.
• Piston Inspection: Check for scoring, ring groove wear, and pin bearing play. Replace if out of spec.
• Cylinder Inspection: Inspect bore for scoring or glaze. Light honing permissible if plating is intact.
• Assembly: Lubricate piston and rings. Use ring compressor. Torque cylinder bolts to 10 Nm (88 in-lb) in crisscross pattern.
• Post-Assembly: Set ignition gap (0.3-0.4 mm). Prime fuel system. Perform break-in (3 tanks at varied RPM).

Fuel System Service

Servicing fuel tank, lines, filter, and pump.

1. Drain fuel tank completely.
2. Remove fuel hose from carburetor and tank. Inspect for brittleness or cracks.
3. Extract fuel filter from tank using hooked wire. Replace filter.
4. Check tank vent for blockage. Clean or replace if necessary.
5. Inspect fuel cap seal and vent.
6. Reassemble with new lines, ensuring secure connections. Pressure test for leaks.

Tip: Use STIHL MotoMix or ethanol-free fuel to prevent carburetor and line degradation.

Ignition System & Electrical

Testing and replacing ignition components.

Spark Test: Remove spark plug, reconnect boot, ground plug against cylinder. Pull starter - look for strong blue spark.

Coil Air Gap: Set between 0.3 mm and 0.4 mm using feeler gauge. Adjust by loosening coil screws.

Switch Testing: Use multimeter to check for continuity in ON/OFF positions.

STIHL EasyStart System: If equipped, check spring mechanism and engagement pawls for wear.

Replacement: If no spark, replace ignition coil (module) with genuine STIHL part.

Cutting Equipment & Bar/Chain

Maintenance of guide bar, chain, and Ematic™ lubrication system.

1. Bar Maintenance: Clean bar groove, flip bar weekly for even wear. Check for straightness and groove wear.
2. Chain Sharpening: Use correct round file size (4.0 mm). Maintain 30° top plate cutting angle, 10° down angle.
3. Depth Gauge Setting: File depth gauges to 0.65 mm using depth gauge tool.
4. Tensioning: Adjust with side-access tensioner when chain is cool. Proper tension: snug against bar but pullable by hand.
5. Oil System Test: Run saw at high RPM pointed at light surface - should throw oil line.
6. Oil Pump Output: Adjust via screw on bottom of saw (if adjustable).

WARNING! Always stop engine before adjusting chain tension. Use gloves when handling chain.

Carburetor Adjustment

Procedure for adjusting H, L, and LA screws.

Screw	Function	Initial Setting	Final Adjustment
L (Low Speed)	Idle and low RPM mixture	1 turn open	Adjust for fastest idle, then rich slightly
H (High Speed)	High RPM mixture and max power	1 turn open	Adjust for max RPM, then lean 1/8 turn (using tachometer)
LA (Idle Speed)	Engine idle speed	-	Set so chain does not move at idle

Process: Start with warm engine. Adjust L screw for smooth acceleration. Adjust H screw for maximum RPM (not exceeding 13,500 RPM). Set LA for steady idle without chain creep. Finalize by checking acceleration and return to idle.

Clutch & Sprocket

Service of centrifugal clutch and drive sprocket.

1. Remove bar, chain, and clutch cover.
2. Use clutch tool to hold drum. Remove clutch nut (left-hand thread).
3. Inspect clutch shoes for wear, cracking, or glazing. Replace if worn more than 50%.
4. Check drum for scoring. Replace if grooves are deep.
5. Inspect needle bearing in crankshaft. Replace if rough or noisy.
6. Replace rim sprocket or spur sprocket if teeth are hooked.
7. Reassemble, torque clutch nut to 40 Nm (30 ft-lb).

Note: Worn sprocket accelerates chain wear. Replace sprocket with every second chain.

Anti-Vibration System

Inspection and replacement of AV mounts.

The MS 250 uses rubber AV mounts at front and rear handles. Over time, these harden and crack.

1. Remove handle assembly screws.
2. Extract old rubber mounts from mounting points.
3. Clean metal surfaces.
4. Press new genuine STIHL AV mounts into position.
5. Reassemble handle, tightening screws evenly to avoid distortion.
6. Check for excessive handle movement after assembly.

CAUTION! Do not operate saw if AV mounts are damaged, as vibration transfer can cause long-term injury.

Troubleshooting Guide

Symptom	Possible Cause	Corrective Action
Engine will not start	No spark, flooded, fuel issue	Check spark, dry plug, verify fuel flow, check decomp valve.
Engine starts then dies	Clogged fuel filter, tank vent, carb adjustment	Replace fuel filter, clean vent, adjust L screw.
Loss of power under load	Clogged air filter, spark arrestor, carb H setting	Clean/replace filter, clean spark arrestor, adjust H screw.
Chain does not oil	Empty oil tank, clogged oil passages, faulty pump	Fill tank, clean bar groove and oil ports, replace pump.
Excessive vibration	Worn AV mounts, unbalanced chain, bent bar	Replace AV mounts, sharpen chain evenly, replace bar.
Chain rotates at idle	High idle speed, worn clutch springs	Adjust LA screw, replace clutch springs/shoes.

Special Tools: STIHL diagnostic tool (for advanced diagnostics), compression tester, tachometer.

Service Support: For technical assistance, contact STIHL authorized service center or visit www.stihlusa.com.