Spark Plug Thread Repair

Damaged spark plug threads in the cylinder head can be serviced using Rotunda Sav-A-Thread Spark Plug Kit 107-R0921 or equivalent.

1. Thoroughly clean spark plug counterbore, seat and threads of all dirt or other foreign material.

CAUTION: The cylinder head must be removed from cylinder block 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 cylinder block 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.

NOTE: The use of power or air-driven tools is not approved for the installation of taperserts. The procedure involves cutting new threads in the spark plug hole. After 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 effect on the life of the cylinder head or spark plug.





2. Start tap into spark plug hole and keep it properly aligned.

As tap begins cutting new threads, apply aluminum cutting oil to tap.

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

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

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





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

NOTE: A properly installed tapersert will be flush to 1.0 mm (0.254 inch) below spark plug gasket seat.

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