Spark Plug Thread Repair

CAUTION: The cylinder head must be removed from the engine before installing a tapersert. If this procedure is done with the cylinder head on the engine, the cylinder walls can be damaged by metal chips produced by the thread cutting process. Do not use power or air-driven tools for installing taperserts. Cylinder head damage may occur.

NOTE: This repair is permanent and will have no effect on cylinder head or spark plug life.





1. Clean the spark plug seat and threads.





2. Start the tap into the spark plug hole, being careful to keep it properly aligned. As tap begins to cut new threads, apply aluminum cutting oil.
3. Continue cutting the threads and applying oil until the stop ring bottoms against the spark plug seat.
4. Remove the tap and metal chips.





5. Coat the threads of the mandrel with cutting oil. Thread the tapersert onto the mandrel until one thread of the mandrel extends beyond the tapersert.





6. Tighten the tapersert into the spark plug hole.

NOTE: A properly installed tapersert will be either flush with or just below the spark plug gasket seat.





7. Turn the mandrel body approximately one-half turn counterclockwise and remove.