Stihl MS250 Chainsaw Service Manual

The Stihl MS250 is a lightweight, professional-grade chainsaw featuring a 45.4cc engine, Easy2Start™ system, anti-vibration technology, Ematic™ lubrication, Quickstop® inertia chain brake, and STIHL Quick Chain Adjuster (QCA). This manual provides comprehensive instructions for maintenance, troubleshooting, repair, and safety procedures to ensure optimal performance and longevity of your chainsaw. Below are key sections covering safety, specifications, maintenance, troubleshooting, and repair.

Safety Information & Warnings

Always wear appropriate PPE: safety glasses, hearing protection, gloves, chainsaw chaps, and sturdy boots. Operate chainsaw with both hands. Ensure chain brake is functional before use.

Specifications & Features

Key components: Engine, guide bar, chain, starter assembly, carburetor, ignition module.

1. Engine: 45.4cc single-cylinder, 2-stroke, air-cooled.
2. Power Output: 2.6 kW (3.5 bhp) at 9,500 rpm.
3. Fuel Capacity: 0.5 L (16.9 fl. oz.).
4. Oil Capacity: 0.26 L (8.8 fl. oz.).
5. Guide Bar Lengths: 16" (40 cm) or 18" (45 cm).
6. Chain Pitch/Gauge: 3/8" PMM, 0.050" (1.3 mm).
7. Weight (powerhead): 5.2 kg (11.5 lbs).
8. Ignition: Electronic, non-adjustable.
9. Carburetor: Zama C1Q-S267 (adjustable H/L).

WARNING! Use only STIHL-approved replacement parts. Modifications void warranty.

Maintenance Schedule

Regular maintenance ensures safety and performance. Follow intervals based on usage hours.

1. Daily/Before Use: Check chain tension, sharpness, bar condition; test chain brake; inspect air filter; verify fuel/oil levels.
2. Weekly (10 hrs): Clean air filter; inspect spark plug; check all fasteners for tightness; clean cooling fins.
3. Monthly (50 hrs): Replace spark plug (BPMR7A); clean fuel filter; inspect fuel lines; check carburetor adjustment.
4. Annually (100 hrs): Replace fuel filter; clean muffler spark arrestor; inspect anti-vibration elements; check clutch drum/sprocket.

CAUTION! Disconnect spark plug wire before performing maintenance.

Engine & Carburetor

• Cylinder: Bore 40.0 mm, stroke 36.0 mm. Inspress for scoring; replace if deep scratches present.
• Piston: Measure ring end gap (0.25-0.50 mm). Replace if worn beyond limits.
• Crankshaft: Check bearings for smooth rotation; no axial play.
• Carburetor Adjustment: Factory settings: L=1 turn out, H=1 turn out. Fine-tune for smooth acceleration.
• Idle Speed: 2,800-3,200 rpm (chain must not rotate).
• Maximum Speed: 13,500 rpm (governed).

Fuel & Lubrication System

Fuel System: Tank, filter, lines, carburetor. Lubrication: Oil tank, pump, delivery line.

Fuel Mix: 50:1 (2% oil). Use STIHL HP Ultra or equivalent ISO-L-EGD certified oil.

Oil Pump: Adjusts automatically to engine speed. Test output: run saw at full throttle against wood; observe oil streak on cardboard.

1. Inspect fuel lines for cracks/hardness; replace if deteriorated.
2. Clean fuel filter every 50 hours; replace annually.
3. Check oil delivery by removing bar and running saw; oil should flow from outlet.

Tip: Always empty fuel tank before storage >30 days.

Ignition System

Components: Flywheel, ignition module, spark plug, stop switch, wiring.

1. Spark Plug: BPMR7A (NGK) or equivalent; gap 0.5 mm (0.020").
2. Ignition Module: Non-adjustable; check for spark with tester (5 mm gap).
3. Stop Switch: Test continuity; should be open when OFF, closed when ON.
4. Flywheel: Check key for shearing; torque nut to 40 Nm (30 ft-lb).

WARNING! Never crank engine with spark plug removed and wire connected (fire hazard).

Chain & Bar Assembly

Supports STIHL Rollomatic® bars and .050" gauge chains.

1. Chain Tension: Adjust via side knob (QCA). Proper tension: chain snaps back when pulled from bar.
2. Sharpening: Use 4.0 mm round file at 30°; maintain equal cutter lengths.
3. Bar Maintenance: Clean groove weekly; flip bar monthly for even wear; dress rails with flat file.
4. Sprocket: Inspect clutch drum sprocket; replace if worn (teardrop shape).
5. Drive Sprocket: 7-tooth standard; replace with bar/chain.

WARNING! Always wear gloves when handling chain. Ensure chain brake is disengaged during tensioning.

Starting System

Easy2Start™ reduces pulling force by 30%. Components: starter pulley, spring, rope, decompression valve.

Decompression Valve: Automatically releases cylinder pressure. Test: press button; should return freely.

1. Starter Rope Replacement: Wind spring 3.5 turns clockwise; align rope groove.
2. Recoil Spring: Lubricate lightly with grease during assembly.
3. Common Issue: Rope retracts slowly – check spring engagement or replace spring.

CAUTION! Keep fingers clear of starter handle during recoil.

Troubleshooting Guide

Reset: For electronic issues, disconnect spark plug wire for 1 minute.

Disassembly & Assembly

General sequence: Remove top cover, air filter, carburetor, cylinder, piston, crankshaft.

1. Label all parts and fasteners.
2. Use STIHL special tools (piston stop, flywheel puller).
3. Clean all parts in solvent; inspect for wear.
4. Apply 2-stroke oil to piston/cylinder during reassembly.
5. Torque cylinder bolts to 10 Nm (7.5 ft-lb) in crisscross pattern.

Tip: Refer to STIHL service manual for detailed exploded views.

Torque Specifications

• Cylinder bolts: 10 Nm (7.5 ft-lb)
• Clutch: 40 Nm (30 ft-lb) – left-hand thread
• Flywheel nut: 40 Nm (30 ft-lb)
• Spark plug: 25 Nm (18 ft-lb)
• Guide bar nuts: 9 Nm (6.5 ft-lb)
• Muffler bolts: 10 Nm (7.5 ft-lb)
• Starter cover screws: 4 Nm (3 ft-lb)

Service: Authorized STIHL dealers only. For support, visit www.stihlusa.com or contact 1-800-467-8445.