Here is what we know:
1. Where the original screw was, the threads are stripped.
2. The hole isn't straight.
3. The owner does't want to remove the shaft.
Here is what we don't know:
1. Was the original hole straight?
2. Is the non-concentricity of the hole to the shaft caused by it not being drilled correctly in the first place?
3. Is the non-concentricity of the hole to shaft only at the end of the shaft caused by a harder bolt working the metal?
4. What is the diameter of the shaft relative to that of the bolt?
5. What makes it so difficult to remove the shaft?
Solutions as posted by me and others:
1. Drill and tap hole to next larger size bolt.
2. Drill and tap for a spring type helicoil.
3. Drill and tap for a Time-Sert.
4. Remove shaft, weld and redrill hole.
Obviously, to do the job right, solution number 4 is the best, especially so since the shaft can be put in a lathe and the hole drilled and tapped true.
Solutions 2 and 3 are worse than solution 1 since the helicoil and the Time-Sert still require that a hole be drilled and tapped, then a threaded insert installed to take the original size bolt. Why not just use a larger bolt and skip the Helicoil or Time-Sert? What am I missing? Why are two threaded objects required to secure one bolt?
Furthermore, a helicoil or Time-Sert would be recommended if the threaded area had to meet a specific size, like a spark plug
. However, in this case, we don't seem to need that.