i recently converted an old puch mountain bike into a singlespeed. no new parts yet, just removed the deraulliers and shortened the chain. the first time i rode, the rear axle on the chain side kept slipping forward in the horizontal dropout. so i cranked down on the nut to tighten it, and kept riding. later, the rear axle and the frame bent, just forward of the axle. i bent the frame back into place and i plan to replace the rear axle and hope for the best, but has anyone had this happen? any idea why? did i take too much slack out of the chain?

I don't know if I understand... Do you have pics?

sorry no pics. imagine this: the chain pulled forward on the rear wheel. the rear axle bent just at the outside edge of the hub, as the axle pulled the hub forward. the frame bent inward at the dropouts just forward of the rear axle. the bend in the frame was in the flat part that includes the droupout.

is the rear wheel bolt on, or does it have a quick release? in my experience, i have never been able to prevent the rear wheel from being pulled over during hard pedaling on a single speed running a quick release.

if your FRAME bent from that little of an issue, I wouldn't ride it.

bolt-on.