My wifes car has some buggered up threads in the spark plug hole. Appearantly it is a common problem. Anyhow, I bought a tap to attempt to chase the threads. I tried to start it, but it's not going to be easy. I was curious if a thread chaser might have threads to start as the tap is wanting to cut new threads. Or should I take the head off and start from the bottom up? I am relativly new to this type of repair, but I am convinced I can do it. Worse case I may have to take the head to a machinest to have a heli coil installed. What are your thoughts?