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?