Spark Plug: Description and Operation

Spark Plug Showing Coated Insulator:

PURPOSE
To start the combustion process, resistor type, tapered seat spark plugs are used on all gasoline engines. No gasket is used on these tapered seat plugs. When replacing spark plugs, use only the type specified. Spark plugs are identified as shown in Figure 1.

OPERATION
Normal service is assumed to be a mixture of idling, slow speed, and high speed driving. Occasional intermittent high-speed driving is needed for good spark plug performance. It gives increased combustion heat, burning away carbon or oxides that have built up from frequent idling, or continual stop-and-go driving.

CONSTRUCTION
These spark plugs have a ceramic insulator that is approximately 6.35 mm (1/8 inch) longer than conventional spark plugs. The longer length spark plugs magnify the problem of cracked insulators because most spark plug sockets are not of sufficient length to properly engage the shell hex. If the spark plug shell hex is not fully engaged in the spark plug socket wrench, the socket may cock at an angle and cause insulator cracking and/or breakage during plug installation or removal.