The photo shows that the crank seated fairly deeply. It was well within the range of what's acceptable. Much deeper, and you run the risk of bottoming out the crank bolt. The taper has a very shallow angle, so even small variations in the taper cause big differences in how deep the crank seats. Since there are tolerances in the dimensions of both BB and crank, you need some margin for these tolerances. If you designed the system that the BB spindle comes within 1 mm of the end of the crank, you'd get 10% where the spindle is a tad small or the crank taper a tad large, and the spindle would extend beyond the edge of the crank. The crank bolt would bottom out, and you couldn't tighten the crank properly.
It's hard to speculate about the reason for the failure. It's not a place where the crank gets stressed in use, only when mounting. It could be that the crank was tightened repeatedly by a previous owner, and thus pulled further and further onto the spindle, until it "burst". (Repeated tightening is not recommended - install the crank and tighten it once 50 miles later. Then leave it alone. After 2 years or so, take it off, inspect it and reinstall it. But don't just tighten it every few months or so.) Another possible explanation is a flaw in the forging. Jan Heine Compass Bicycles Ltd. www.compasscycle.com On Thursday, January 7, 2016 at 11:57:38 AM UTC+9, Ron Mc wrote: > > I think Peter's dead on, it may have not seated deeply enough, and I maybe > contact stresses were too high. > > > <http://img.photobucket.com/albums/v728/bulldog1935/Raleigh/700c/aP1207650.jpg> > > or it may have just been seated too many times on too many tapers. I > didn't know the age of it, it was a used ebay purchase. > -- You received this message because you are subscribed to the Google Groups "RBW Owners Bunch" group. To unsubscribe from this group and stop receiving emails from it, send an email to rbw-owners-bunch+unsubscr...@googlegroups.com. To post to this group, send email to rbw-owners-bunch@googlegroups.com. Visit this group at https://groups.google.com/group/rbw-owners-bunch. For more options, visit https://groups.google.com/d/optout.
