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It's a bodgy old hack, but I've seen this work before:
- Cover the pedal thread in grease. Lots of grease. This cannot be emphasised enough.
- Smear JB Weld (the proper kind, not the quick-setting kind) on the inside of the crank threads.
- Thread the pedal in from the back of the cranks.
- Smear the excess JB Weld which gets pushed out around the face of the crank and scrape off any excess.
- Wait for the JB Weld to set (24 hours to be on the safe side)
- Hope you added enough grease so that the JB Weld doesn't stick to the pedal.
JB Weld is amazing stuff. Part of the engine block on my old race car was held together using it, after I cracked it overtightening a tapered oil pressure sender fitting. If you don't add enough grease to the pedal threads, and the JB Weld bonds the pedal to the crank, it's never coming out again without copious amounts of drilling.
The other option is to build up the damaged thread with JB Weld or (if you have an AC TIG welder) with weld, and then retap it from the back, but that requires a 9/16" tap. And possibly an AC TIG welder.
- Cover the pedal thread in grease. Lots of grease. This cannot be emphasised enough.
Brommers-
Yes this is the kind of thing that I was wondering about. It's a bit awkward because the thread is knackered only on one side of the outer end, so the area that needs fixing/gap filling is a sort of rounded wedge. Also, I have wound the pedal in from the back, but the axle doesn't reach all the way through to the outer face, which is the questionable bit. In the above method is it possible to let the JB weld semi-harden, "tap" it with the pedal and then remove the pedal again to allow it to fully harden?
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This JB Weld trick sounds like a proper evil genius hack if it works.
A less genius approach would be to simply araldite (epoxy) a pedal into the crank, preferably a pedal that is easily serviceable. Clean the crank and pedal threads first. Obviously it's never coming out again but should still be serviceable.
ffm
Ndeipi
Is there a "it'll do" repair for a partially mangled thread. I've just got a bike where the pedal was put in diagonally (on the DS surprisingly). The inner 3-4 threads or intact but one side of the outer few threads is mangled. I can tighten it down and I think it will be fine, but is there anything I could add to give a bit of contact and fill the gap between the threaded section of the pedal axle and the mangled part of the crank thread. I could just add loads of threadlock, but is there something I could leave mostly harden off and then wind the pedal into?