Bent one piece crank...

[flatblack50]

Hello, I just picked up a 1920's bike with a bent one piece crank. It's bent on the left side. I'm wondering if I heat it up and bend back on the pedal, if I can straiten it... But since it's forged i'm worried that the crank might becoming brittle. The crank is very hard to find... So i'd like to try to fix it. Any ideas?

 

[Crassly]

I have bent back a number of them. I have just done them cold. I figure they got bent that way, they should be able to be straightened that way. I use a Park frame straightener, but I'm sure you could improvise with a piece of pipe or square tubing. If you do happen to break it, let me know, I might have a replacement that would work.

 

[flatblack50]

Thanks! Ya, I might have to just swap out the crank for now. It's one of the "diamond" cranks though. On the outside it has to flat edges instead of being round like most. I'll try to add pics later.

 

[TornadoDave2]

I've straightened a number of old Schwinn one-piece cranks, and have found that they never break, even when bent cold. They must have used good metal back then. My preferred method is the Armstrong Proceedure..... where you put one arm in a bench vise and use a long pipe cheater bar to armstrong it back straight.

One caution: Newer chinese cranks may not be as good as old Schwinn cranks, so they may break.

 

[c.p.odom]

Align it cold. I have done many and always do it before chroming. On every bike I ever restored I aligned the frame, fork, stem, cranks, pedal spindles, etc. Lost of small and large bends happen over the years. The hardest to align are springer forks but well worth the trouble.

 

[deorman]

Unless you pedal bomb like a kid or mountain biker/bmxer, or it's bent badly, you can probably fix it. Unlike with repeated blow forging, or drawing (rolling or extrusion) however, the crystalline structure of a stamp-forged blank is pretty large and disorganized. Very strong, but also brittle. If you feel it getting easier to bend, or see evidence of cracking, I'd say toss it. :|
I wouldn't use heat either, an amateur re-tempering it properly is pretty unlikely.