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[Closed] facing a bb??
i was chatting to my mate on a ride the other day about facing a frame, and we couldn't see the logic..
as i understand, you face a frame to make sure that the bb shells are directly opposite and facing each other. however, if a bb edge wasn't faced, and was, say, 1/2mm out, what would the impact be? surely due to the bb thread, the cup won't align to the outer edge of the bb shell, as that would mean every thread would have to become crossed? in addition, i don't figure there's enough flex in the bb cup itself to fit both the thread and the shell edge? so all that would happen is the bb shell would be tighter against one part of the shell than another? this could, obviously, lead to it coming loose a little prematurely but this doesn't appear to be what everyone is worried about?
have i missed something?
H
have i missed something?
yes
hours of protracted argument over the necessity of BB facing, whether external BBs are any cop and what was wrong with the internal ones 🙂
There's a bit of movement in a bb cup when nearly screwed all the way in, so it in theory can happen.
Whether it does matter is contentious. In theory there's no difficulty that a mis-aligned bearing will wear out more quickly. There are many who will swear blind that it does/doesn't matter on an average frame.
You may have missed the fact that Race Face cranks need an exact width BB shell to avoid destroying the BB bearings through excessive preload if the shell's too wide(much the same effect as overtightening a Shimano preload cap).Other than that, not really seen any definitive evidence that it's needed.
Your crank arms will come flying off and you will die (probably)