@seven
If the threads have gone bad, you have to use the Helicoil Thread repair method. However, my brother uses it in his line of work. I have never seen it used by some kharadiya.
Also, i think (but there can be another way) to avoid small metal filings being dropped in the cylinder, you'ld rather want to remove the head and then then proceed with the repair job.
What my sibling uses