There are two types of thread repair inserts. One is a solid sleeve, the other is a wire coil. The coil wire insert is designed for a smaller size thread and does require a special tool for insertion. (The K-D tool that I've seen taps a thread designed for the solid inserts, not the coil wire insert.)
As far as I'm aware, all the solid type inserts are the same thread size and can be inserted using a spark plug, including one also made and branded by helicoil. (If not, just get the matching insert for the tap you used!) If the tap you used is designed for the wire coil insert, the thread/hole is too small for the solid inserts. I'm not sure, but I don't think the wire coil insert will thread into a hole tapped for the solid insert either.
I doubt the head has to come off. You must simply obtain the correct insert for the tap used. When you sort it out, I would loctite (green) the insert in otherwise there is apparently a good chance it will come out in the future with the spark plug.
Last edited by deaconblues; 10-04-2003 at 06:12 AM.