Spark Plug Thread Repair

DESCRIPTION
Damaged spark plug threads in the cylinder head can be serviced using Rotunda Metric Thread Repair Set Kit or an 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 screw into the cylinder head while the inside threads are for the spark plug (12405). This thread service is permanent and will have no affect on cylinder head or spark plug life.

CAUTION: Do not use power or air-driven tools to install the inserts.

Engine Damage Hazard
The cylinder head must be removed from the engine before installing an insert. 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.

PROCEDURES
1. Thoroughly clean the 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 the new threads, apply aluminum cutting oil to the tap. Continue cutting threads and applying oil until the stop ring bottoms against the spark plug seat.
3. Remove the tap. Remove all metal chips using compressed air.
4. Coat the threads of the mandrel with cutting oil. Thread the insert onto the mandrel until one thread of mandrel extends beyond the insert.

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

5. Thread the insert into the tapped spark plug hole using a torque wrench. Continue tightening the mandrel until the torque wrench indicates 61 Nm (45 ft. lbs.).
6. To loosen the mandrel for removal, hold the mandrel stationary and turn the mandrel body approximately one-half turn. Remove the mandrel.