stihl ms 250 service manual pdf

The STIHL MS 250 is a professional-grade chainsaw designed for demanding cutting tasks. This service manual provides comprehensive information for maintenance, troubleshooting, and repair of the MS 250 model. It covers safety procedures, technical specifications, engine components, fuel system, ignition system, cutting equipment, and detailed step-by-step repair instructions. Below are key sections for safety, features, maintenance procedures, specifications, and troubleshooting.

Features at a Glance

Key components: STIHL 2-MIX engine, QuickStop® inertia chain brake, Ematic™ lubrication system, side-access chain tensioner, and anti-vibration system.

Safety Information

Always wear protective equipment and follow safe operating procedures.

1. Personal Protective Equipment (PPE): Wear safety glasses, hearing protection, gloves, chainsaw chaps, and sturdy boots.
2. Pre-Operation Check: Inspect chainsaw for damage, ensure chain brake functions, check chain tension and sharpness.
3. Safe Starting: Place on ground, engage chain brake, hold front handle with left hand, step on rear handle.
4. Operation: Maintain secure footing, keep bystanders away, be aware of kickback zone.

WARNING! Failure to follow safety instructions can result in serious injury or death. Always refer to the operator's manual before use.

Maintenance Schedule

Regular maintenance ensures optimal performance and longevity.

1. Daily/Before Use: Check chain tension, sharpness, and lubrication. Inspect for loose fasteners.
2. After 5 Hours: Clean air filter, check spark plug.
3. After 20 Hours: Clean spark arrestor screen (if equipped), check fuel filter.
4. After 100 Hours: Replace fuel filter, clean carburetor (if necessary), check cylinder and piston.
5. Annually: Replace spark plug, clean cooling fins, inspect anti-vibration elements.

CAUTION! Use only STIHL-approved parts and lubricants. Disconnect spark plug wire before performing maintenance.

Specifications

• Engine: STIHL 2-MIX, 45.4 cc, single cylinder, air-cooled.
• Fuel/Oil Mix: 50:1 ratio using STIHL HP Ultra or equivalent ISO-L-EGD certified oil.
• Idle Speed: 2,800 RPM.
• Maximum Power Speed: 9,500 RPM.
• Ignition: STIHL Electronic Ignition (CDI).
• Carburetor: Zama C1Q-S series, adjustable H and L jets.
• Starter: STIHL Rewind starter with decompression valve.
• Vibration Damping: STIHL anti-vibration system.
• Warranty: Limited warranty period - refer to STIHL warranty statement.

Engine Components

Major engine components: Cylinder, piston, crankshaft, connecting rod, bearings, seals.

Cylinder: Nikasil-plated aluminum cylinder. Piston: Single-ring piston with intake and transfer ports. Crankshaft: One-piece crankshaft with ball bearings. Seals: Lip seals prevent air leaks. Cooling: Aluminum fins with flywheel fan.

Service procedures include: Measuring compression, inspecting cylinder scoring, checking piston clearance, replacing crankshaft seals.

Fuel System Service

Components: Fuel tank, filter, lines, carburetor, purge bulb.

1. Fuel Filter Replacement: Drain tank, remove filter through filler neck using hook tool.
2. Carburetor Adjustment: Initial settings: L - 1 turn open, H - 1 turn open. Fine-tune at operating temperature.
3. Carburetor Cleaning/Repair: Disassemble, clean jets and passages with compressed air. Replace diaphragms and gaskets if hardened.
4. Fuel Lines: Inspect for cracks; replace if leaking or brittle.

Tip: Always use fresh fuel mixture. Stale fuel can cause starting and performance issues.

Ignition System

STIHL Electronic Ignition Module (CDI), spark plug, stop switch, wiring.

1. Spark Plug: NGK BPMR7A or equivalent. Gap: 0.5 mm (0.020").
2. Ignition Module Testing: Check for spark with tester. Resistance values: Primary coil 0.18-0.27 Ω, Secondary coil 7.5-11.5 kΩ.
3. Stop Switch: Test continuity; switch should be open when OFF, closed when RUN.
4. Air Gap: Adjust between flywheel and ignition module to 0.3 mm (0.012").

WARNING! Never check for spark by holding plug against cylinder. Use approved spark tester.

Cutting Equipment

Guide bar, saw chain, sprocket, chain tensioner, oil pump.

1. Chain Tension: Adjust so chain snaps back when pulled from guide bar.
2. Bar Maintenance: Clean bar groove, flip bar regularly for even wear.
3. Sprocket: Replace if worn (teardrop shape on drive links).
4. Oil Pump: Check output; adjust if necessary (MS 250 has adjustable pump).
5. Chain Sharpening: Maintain correct filing angle (30°) and depth gauge clearance.

CAUTION! Always stop engine before adjusting chain tension. Use proper chain brake when not cutting.

Troubleshooting

Compression Test: Minimum 110 psi for proper operation.

Disassembly & Assembly

Step-by-step procedures for major component removal.

1. Remove top cover: Remove screws, disconnect wiring connectors.
2. Remove fuel tank: Drain fuel, disconnect lines, remove mounting screws.
3. Remove cylinder: Remove muffler, decomp valve, cylinder bolts.
4. Remove crankshaft: Requires special puller tools for bearings and seals.
5. Reassembly: Use new gaskets and seals. Torque fasteners to specification.

Torque Values: Cylinder bolts: 10 Nm (88 in-lb), Clutch: 40 Nm (30 ft-lb), Spark plug: 25 Nm (18 ft-lb).

Parts List & Diagrams

Exploded view diagrams with part numbers for ordering genuine STIHL parts.

• Group 1: Engine Components (Cylinder, Piston, Crankshaft)
• Group 2: Fuel System (Tank, Carburetor, Lines)
• Group 3: Ignition System (Module, Flywheel, Switch)
• Group 4: Cutting Equipment (Bar, Chain, Sprocket)
• Group 5: Covers and Handles
• Group 6: Anti-Vibration System
• Group 7: Starter Assembly
• Group 8: Lubrication System

Note: Always use STIHL part numbers when ordering replacements. Non-genuine parts may affect performance and safety.

Service Support: Contact authorized STIHL servicing dealer or visit www.stihlusa.com