Spark Plug: Testing and Inspection

INSPECTION AND REPAIR
Spark plug inspection is an excellent way to determine overall engine performance and efficiency.
1. Check the electrodes and the insulators for cracks. Replace if faulty.
2. Check the electrodes for wear and replace as necessary.
3. Check the gaskets for damage and replace as necessary.





4. Check the insulation resistance with an ohmmeter. Replace if found to be defective.





5. Spark plug gap should be 1.05 mm (0.04 in.).
If spark plug fouling is excessive, check the fuel and electrical systems for possible causes of trouble. If fuel and electrical systems are normal, install spark plugs of a higher heat range.
If burning of the insulator and electrodes is considerable, install spark plugs of a lower heat range.

Sooty Spark Plugs
If the spark plug electrodes and insulators are fouled with carbon or oil, the engine will not operate efficiently. There are a number of possible causes.
- The fuel mixture is too rich.
- The ignition timing is retarded.
- There is oil in the combustion chamber.
- The spark plug gap is not set correctly.
In most cases of this sort, the problem can be corrected by using hotter type spark plugs.

Running Too Hot
This condition is characterized by scorched or heavily oxidized electrodes and a blistered insulator nose. Some possible causes are listed below.
- The fuel mixture is too lean.
- The ignition timing is too far advanced.
- The heat range is incorrect.
In most cases of this sort, the problem can be corrected by using colder type spark plugs.

Insulation Resistance
Check the insulation resistance using a 500 volt megohm meter.
Replace the spark plug if it is found to be defective.

Insulation resistance: 50 Meg Ohms or more.

Spark Plug Cleaning Procedure
Clean the spark plugs with a spark plug cleaner.
1. Raise the grounded electrode to an angle of 45° to 60°.
2. If the hot tip insulator nose is damp or wet, wipe it dry before cleaning it.
3. When cleaning, use a wiping motion to facilitate cleaning of confined areas at the inner part of the insulator.
4. When the spark plug is thoroughly cleaned, check to make certain the porcelain insulator is free from cracks.
5. Clean the threads and metal body, using a wire brush.
6. If the insulated electrode is worn excessively, file the tip of the electrode flat with a file.
7. Adjust the spark gap by bending the grounded electrode.