Question on thread repair, exhaust stud.

[mike96]

Sorry no pictures, my phone is giving me issues right now and wont let me upload anything. Anyway I was wondering if anyone knows how large diameter and how deep you can drill the head at the bottom left exhaust stud, (the 10mm one closest to the thermostat housing). It has already had a repair done to it once with the wrong thread pitch stud and that helicoil felt like it was pulling out so I want to repair it with a solid insert. However, in order to replace it with the correct thread pitch stud it will need to be a bigsert insert witch is over 1/2 inch in diameter and I am worried about hitting an oil or coolant passage.

Thanks
Mike