Craftsman 18 40cc Chainsaw Repair Manual

The Craftsman 18-inch 40cc Gas Chainsaw is a powerful tool designed for demanding cutting tasks. This manual provides comprehensive repair, maintenance, and troubleshooting guidance for model series 358.xxxxxx. It covers safety procedures, engine components (fuel system, ignition, cylinder/piston), cutting assembly (chain, bar, sprocket), carburetor adjustment, routine maintenance, and common fault diagnosis. Always disconnect the spark plug before any repair.

1. Safety Precautions 2. Specifications & Identification 3. Tools & Workshop Requirements 4. Engine Disassembly & Assembly 5. Fuel System Repair 6. Ignition System Service 7. Cutting Assembly Maintenance 8. Carburetor Adjustment & Tuning 9. Routine Maintenance Schedule 10. Troubleshooting Guide 11. Parts List & Exploded Diagrams

Safety Precautions

Before any repair, ensure the chainsaw is cool, the spark plug wire is disconnected, and all fuel is drained. Wear cut-resistant gloves and safety glasses.

Hazard	Precaution
Fuel Fire/Explosion	Drain fuel in well-ventilated area away from sparks or flame.
Accidental Start-up	Always disconnect spark plug boot before working on engine or chain.
Sharp Chain	Handle chain by the drive links; use a chain guard or vise.
Hot Surfaces	Allow muffler and cylinder to cool completely before disassembly.
Toxic Fumes	Work in a ventilated area when cleaning carburetor or fuel tank.

Specifications & Identification

Locate the model and serial number plate on the rear housing or crankcase.

Engine: 40cc 2-cycle air-cooled gasoline engine.
Fuel Mix: 50:1 (High-quality 2-cycle oil with 89+ octane gasoline).
Bar Length: 18 inches (Oregon or equivalent).
Chain Pitch/Gauge: .325" pitch, .050" gauge (Check spec plate).
Ignition: Electronic, air gap ~0.3mm.
Carburetor: Walbro or Zama diaphragm type with H, L, and idle adjustment screws.
Spark Plug: Champion RCJ7Y or equivalent, gap 0.025".

Tools & Workshop Requirements

Basic mechanic's toolset plus specialty tools.

Socket set (including 13mm for clutch, 8mm/10mm for covers).
Torx bits (T27 for bar nuts common).
Chain breaker/spinner tool.
Compression tester (expected: 120-150 psi).
Carburetor adjustment tool (splined or screwdriver type).
Piston stop or strap wrench for flywheel removal.
Feeler gauges for ignition air gap.
Mityvac or equivalent for pressure/vacuum testing fuel system.

WARNING! Use proper tools to avoid damage to fasteners and components.

Engine Disassembly & Assembly

Procedure for accessing cylinder and crankcase.

Remove top cover, air filter, and carburetor box.
Disconnect fuel line and impulse line from carburetor.
Remove muffler and spark plug.
Remove cylinder cover/base screws; lift off cylinder carefully.
Inspect piston for scoring, rings for free movement.
For crankshaft/seal replacement, split crankcase after removing clutch, flywheel, and all fasteners.
Assembly Tip: Use new gaskets; torque cylinder bolts in crisscross pattern to spec (typically 10-12 ft-lb).

CAUTION! Label all parts and fasteners. Do not force crankcase halves.

Fuel System Repair

Addressing fuel delivery issues: tank, lines, filter, pump.

Components: Fuel tank, fuel filter, fuel lines (supply and return), impulse line, carburetor diaphragm pump.

Common repairs: 1. Clogged Fuel Filter: Replace annually; located in tank. 2. Cracked Fuel Lines: Replace all lines with ethanol-resistant tubing. 3. Faulty Fuel Pump Diaphragm: In carburetor kit; test with Mityvac. 4. Leaking Tank Vent: Clean or replace tank cap assembly.

Ignition System Service

Testing coil, spark plug, stop switch.

Check spark plug: Replace if fouled or electrode worn; set gap.
Test for spark: Ground plug to cylinder, pull starter. No spark? Proceed.
Check kill switch wire: Disconnect from coil; retest for spark.
Test ignition coil resistance: Primary ~0.5-2Ω, Secondary ~5-15kΩ (refer to manual).
Check flywheel magnets and coil air gap: Adjust to 0.3mm with feeler gauge.

Tip: Weak or intermittent spark often indicates failing coil or poor ground connection.

Cutting Assembly Maintenance

Chain, bar, and drive sprocket service.

Component	Maintenance	Specification
Guide Bar	Clean groove, flip weekly, file rails if burred.	18" length, .050" gauge
Chain	Sharpen with round file (5/32" common), depth gauge setting 0.025".	.325" pitch, 72 drive links (verify)
Drive Sprocket	Replace if worn (teeth hooked). Rim type or spur.	Match chain pitch
Clutch	Inspect shoes for wear; clean drum.	Engages ~2500-2800 RPM
Oil Pump	Clear passage, test output. Adjust if adjustable.	Delivers oil to bar groove

Carburetor Adjustment & Tuning

Standard initial settings for Walbro WT series carburetor.

Initial Settings (screws lightly seated): L (Low) = 1-1/4 turns out, H (High) = 1 turn out, Idle = 1 turn out.
Start engine, warm up for 5 minutes.
Adjust idle speed screw so chain just stops moving.
Fine-tune L screw for smoothest acceleration from idle.
Under load, adjust H screw for maximum RPM, then richen slightly (approx 1/8 turn) for 4-stroke "burble".
Re-check idle after H adjustment.

WARNING! Over-leaning H screw can cause engine seizure. Use tachometer for best results (max RPM ~13,500).

Routine Maintenance Schedule

Preventative maintenance checklist.

Before Each Use: Check chain tension, bar oil level, fuel mix, air filter cleanliness.
Every 10 Hours: Clean air filter, inspect spark plug, clean cooling fins.
Every 20 Hours: Sharpen chain, clean bar groove, check clutch and sprocket.
Every 50 Hours: Replace fuel filter, inspect fuel lines, clean carburetor screen.
Seasonal/Annual: Replace spark plug, decarbon exhaust, pressure test crankcase seals.

Troubleshooting Guide

Symptom	Possible Cause	Corrective Action
Engine won't start	No spark, flooded, fuel issue	Check spark, plug condition; dry plug; verify fuel delivery.
Starts then dies	Clogged fuel filter, bad pump diaphragm	Replace filter; rebuild carburetor.
Lacks power under load	Clogged air filter, exhaust screen, incorrect H setting	Clean filter/screen; tune H screw.
Chain won't turn	Clutch worn, sprocket seized, chain too tight	Inspect clutch/sprocket; loosen chain.
Excessive vibration	Unbalanced flywheel, bent crankshaft, loose components	Check flywheel key; inspect crank; tighten mounts.
Oil not dispensing	Clogged oil port, faulty pump, wrong oil viscosity	Clean bar hole and tank filter; test pump output.

Reset: After major repair, retune carburetor from initial settings.

Parts List & Exploded Diagrams

Refer to Craftsman parts catalog for model 358.xxxxxx. Key replacement part numbers (example):

Cylinder/Piston Kit: 530069854
Carburetor Kit (Walbro): K20-WAT
Ignition Coil: 530035722
Clutch Assembly: 530069852
Oil Pump: 530041506
Fuel Line Kit: 530069853

For diagrams and latest parts, visit www.searspartsdirect.com or contact Craftsman support at 1-888-331-4569.