Spark plugs should be cleaned about every 250 hours of use. The type of plug should be changed to correspond to the kind of fuel used. A "hot" plug, one with a long distance for the heat to travel from point to gasket in the shell, is used for heavy fuel. A "cold" plug, one with a short distance for heat to travel from point to gasket in the shell, is used for gasoline.

Cleaning procedures:

• Brush or blow dirt from around the spark plug base.

• Remove the plug with a correctly fitted wrench.

• Examine the porcelain insulator and points. If the insulator appears to be melted or blistered, cracked or broken, and the points seem unduly burned it is evident that the plug is operating too hot and it should be replaced with a colder plug. If the plug is fouled excessively with carbon it apparently is operating too cold and it should be replaced with a hotter plug. Plug and engine manufacturers recommend specific plugs for specific uses. Even the correct style of plug will accumulate some carbon and the electrodes will scale to a certain extent. Carbon accumulation tends to allow leakage of electricity with the possibility of a complete short. Corroded or scaled points tend to weaken the spark.

• Misfit plugs should be replaced with the proper plugs.

• Clean plugs in a sandblast cleaner, if possible. If one is not available, clean with a wire brush.

• Regap the plug points. Use round gauge, and bend outside electrode to the correct gap as recommended by the manufacturer. Gap varies widely among engines, from 20/000 to about 40/000 inch. Gap specs for many models of tractors are available here..
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