tapped out head perfectly with tool, then inserted heliocoil (napa brand) on sparkplug as directed and tried to install unit into newly threaded sparkplug hole, no way, could not catch a thread and ended up buggering top thread, seems to me a mismatch somewhere..Napa now says that maybe the napa brand insert is not compatible with K-D brand tap threads, I am also being told that contrary to what I am being told that there is a special tool for inserting heliocoil into head and not putting it on sparkplug..I am in big trouble here as machine shops say now head must come off for them to work on it. has anybody done this job? thanx