Stripped rear derailer thread
So I picked up a mountain bike from a local auction for $50. It was missing a seat and the rear derailer was bent and broken off. At the time the threads on the hanger where the rear derailer attaches worked, though they were pretty messed up. After messing with it to much, and trying to re tap the hole it became to stripped to use.
So I have this nice new bike that's all cleaned up, new break pads, new seat etc. .. but I can't attach the rear derailer.
I can't just drill out the hole and use a bigger bolt because the the bolt on the derailer is a special shape, and part of a berring.
The best fix I've found after searching online are these coil thread repair inserts. FIX-A-THRED, Helicoil are two brands that I've found. Has anyone has any experience with these?
The only problem is this was supose to be a cheap bike and a helicoil kit is around $20. So I'm looking for other suggestions on how to fix this.
I have a tap that is the right size, but I don't have access to any sort of welder. Is there any other material that I could plug the hole up with before I drill it out and re-tap it. Polyester resin? Solder? Anyway thanks in advance.