Spark Plug: Service and Repair

REMOVAL
1. Remove the ignition coil on plug.







2. Remove the spark plugs.

NOTE: Use compressed air to remove any debris from the spark plug well before removing the spark plugs.








3. Inspect for gap bridged.
- Identified by deposit build-up closing gap between electrodes.
- Caused by oil or carbon fouling. Clean spark plug.







4. Inspect for oil fouled.
- Identified by wet black deposits on the insulator shell bore electrodes.
- Caused by excessive oil entering combustion chamber through worn rings and pistons, excessive clearance between valve guides and stems, or worn or loose bearings. Correct oil problem.
- Replace spark plug.







5. Inspect for carbon fouled.
- Identified by black, dry fluffy carbon deposits on insulator tips, exposed shell surfaces and electrodes.
- Caused by too cold a plug, dirty air cleaner, damaged fuel pump, too rich a fuel mixture or excessive idling.
- Clean spark plug.







6. Inspect for normal burning.
- Identified by light tan or gray deposits on the firing tip.







7. Inspect for pre-ignition.
- Identified by melted electrodes and possibly blistered insulator. Metallic deposits on insulator indicate engine damage.
- Replace spark plug.







8. Inspect for overheating.
- Identified by a white or light gray insulator with small black or gray brown spots and with bluish-burnt appearance of electrodes.
- Caused by engine overheating, wrong type of fuel, loose spark plugs, too hot a plug, low fuel pump pressure or incorrect ignition timing. Replace spark plug.







9. Inspect for fused spot deposits.
- Identified by melted or spotty deposits resembling bubbles or blisters.
- Caused by sudden acceleration. Clean spark plug.

INSTALLATION







1. Adjust the spark plug gap as required.







2. Install the spark plugs.