General Description

These engines use resistor-type, tapered-seat spark plugs. These plugs do not have a gasket. These spark plugs are High Efficiency (HE) spark plugs that have a fine wire electrode, a nickel plated shell, and a platinum pad across from the electrode. These features give the HE spark plug long life and durability. For correct spark plug gap information,

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 or breakage during plug installation or removal.

Normal or average service is assumed to be a mixture of idling, low speed, and high speed operation with some of each making up the daily total driving. Occasional or intermittent high speed driving is essential for good spark plug performance. High speed driving provides increased and sustained combustion heat that burns away any excess deposits of carbon, or oxide, that may accumulate from frequent idling, continual stop-and-go, or slow speed driving. An insulating boot made of special heat-resistant material that covers the spark plug terminal, and extends downward over a portion of the plug insulator. Protects the spark plugs. These boots prevent flash-over with resultant misfire of the engine, even though a film is allowed to accumulate on the exposed portion of the plug porcelains.

Do not mistake corona discharge for flash-over or a shorted insulator. Corona discharge is a steady blue light appearing around the insulator, just above the shell crimp. This is the visible evidence of a high-tension field, and has no effect on the ignition performance. You usually can only detect corona discharge in darkness. This discharge may repel dust particles, leaving a clear ring on the insulator just above the shell. This ring is sometimes mistakenly regarded as evidence that combustion gases have blown out between the shell and the insulator.