The spark plugs may become dislodged from the cylinder heads. A loud popping noise can be heard and a subsequent misfire experienced. The threads on the spark plug ports in the cylinder head(s) can become stripped or missing when the spark plug is dislodged. The threads in cylinder heads may be replaced using “Lock-N-Stitch” aluminum inserts. Our technicians tell us thread replacement is performed when the vehicle is out of base warranty. Vehicles under base warranty receive a new cylinder head.