A helicoil is a coil of spring steel that is inserted in an oversized tapped hole. The inside of the coil matches the original thread. Since it is spring steel, it fits snugly and essentially restores the origninal thread if it is all done correctly. You will need enough room to do the drilling and tapping, so it may be a job with the engine out. Do a Google search on Helicoil and you will find a lot of information and sources, or just ask any good auto mechanic.