cracked bottom bracket shell
I built a frame about 2 and a half years ago. and the bottom bracket seat tube lug area cracked. looks like it was around the shoreline, what do i do and is there a easy way to fix this problem.
First, post some clear images of the bottom bracket.
That's the only way others can really access what needs to be done.
Is it the shell that is cracked, or the seat tube?
I've seen this happen with bulge-formed BB shells. You can repair it, but it is a big job. First you need to cut the shell into several sections, then sweat each section off the tubes, clean them all up, and braze in a new shell. If the new shell is different from the old one, you may also need to replace the chainstay bridge. And of course you'll need to repaint.
Thinking like a welder. but in miniature..
Dremel a V into the crack and run a tig pass over it, . file the bead down.. though it may likely locally melt some of the brass that was used to build it in the 1st place.
a bulge formed BB should have drawn brass in under that spot.. .. perhaps you can ride with a helmet cam mounted there looking at the site,
and see how much it moves .. as you ride .. maybe live with it as you build another one to replace it.
Is not better just go and change the BB shell? I have seen this stuff fixed just brazing it from out side but since lugs are available and looks like you know how to braze why not just change the BB shell for a new one?
from what I think I see, you didn't get good penetration over on the drive side, and now that has resulted in a crack through the bb shell. If that's the case, you are going to have problems unless you fix the underlying problem.
I think this is one to strip the paint, get two torches on it, and yank it apart, and look at what you did. I agree the brazing penetration was not uniform. Kind of amazing how lugged construction can be so durable even when not perfect.
Originally Posted by unterhausen