Spark Plug Thread Service

CAUTION: The cylinder head must be removed from engine before installing a tapersert. The service procedure includes a thread cutting process which produces metal chips. Performing this procedure while the cylinder head is on the engine will cause metal chips to fall into the cylinder. Once in the cylinder, these chips can damage the cylinder wall when the engine is started.





Damaged spark plug threads in the cylinder head can be serviced using Rotunda Tapersert Installation Kit 107-R0921 or equivalent.

The procedure involves cutting new threads in the spark plug hole. After the rethreading operation, a tapered sleeve will be installed in the cylinder head. The sleeve is threaded on the inside and outside. The outside threads into the cylinder head while the inside provides new threads for the spark plug.

This service is permanent and will have no affect on cylinder head or spark plug life.
1. Thoroughly clean spark plug counterbore, seat, and threads of all dirt or other foreign material.
2. Start the tap into the spark plug hole, being careful to keep it properly aligned. As the tap begins cutting new threads, apply aluminum cutting oil to the tap.

Continue cutting the threads and applying oil until the stop ring lightly bottoms against the spark plug seat.

NOTE: The use of power or air-driven tools is not approved for the installation of taperserts.

3. Remove the tap. Remove all metal chips using compressed air.





4. 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.
5. Thread the tapersert into the tapped spark plug hole using a torque wrench. Continue tightening the mandrel until the torque wrench indicates 61 Nm (45 ft. lbs.).

NOTE: A properly installed tapersert will be flush to one millimeter (0.03937 inch) below spark plug gasket seat.





6. To loosen the mandrel for removal, hold the mandrel stationary and turn the mandrel body approximately one-half turn counterclockwise. Remove the mandrel.