Workshop

Thread repair on a cock eyed tapped hole:

Working on a dismantled gear box, this tapped hole should always be rethreaded with helicoil or an insert.
The old threads are often stripped and you need to tighten well that bolt.

This case had old repairs and was welded around the tapped hole - too big and cock eyed to drill for a 1/4" UNC helicoil.
It needs filling up with new weld. For good results, cut away half the wall to eliminate air holes.

After welding, due to material distortion, the sealing surface needs to be reworked.

With the help of the primary case drill the new tap hole - not deeper than 1/2", otherwise you'd break through.