Just saw yeserdays post about repairing threads in a head. I've used Helicoils on numerous occasions but have had better luck over the years using a different type insert from Time-Sert. They are made similar to a Helicoil but the insert is solid instead of just being an open coil. You can look at the way they make them but basically they time the internal and external thread to make a solid bodied insert but still have a wall thickness as nearly thin as a regular, old style helicoil. I've used them with great success in applications where a regular helicoil has failed. They make a variety of different kinds/sizes for just about anything be it metric, standard,or spark plug thread repairs. They are available directly from Timesert or you can also get them from places like McMaster Carr, etc.
Time Sert
Time Sert
