Years of operating debris can accumulate in a spark plug port to such an extent that a clean-out brush cannot remove enough to restore the spark plug port dimensions to SAE J548d standards. This is typically the case when thread anti-seize compound is so routinely used that it eventually fuses to the cast iron. When this is the situation, the port threads may have to be re-cut.

By hand, on the engine, when the spark plug port is at the bottom of a deep spark plug well, the tap must be fitted into an extended-length holder. The standard, extended-length holders are sized for the majority of deep spark plug well cylinder heads that are in service. Special lengths can be made available on request. Please consult our recommendation charts (page 11 of the STITT Professional Spark Plug Installation Manual for Integral Compressor Engines, PSIM / 8-99) for the engine that you are interested in tapping.