I was helping my brother remove and clean his chain and he noticed his crank was dirty plus the bearing dust cap wasn’t staying on. So figure easy enough to remove the crank and regrease the dust caps. So I helped him remove the hollow tech crank and clean it up. Then comes time to reinstall the crank. Put it in and noticed that the crank is way too close to the frame. Was thinking that we missed a spacer or something. Then I started looking into the BB which I believe to be a t47a. I am very familiar with t47 but never messed with the A variate which is asymmetrical. I guess the drive side isn’t a cup with a bearing but a threaded ring that the non drive side press through. Noticed that the drive side cup moves inside the frame and then about flush being moved by hand. Exposing the threads that it should be threaded on. Which seemed very weird to me. So I am thinking that the middle section broke and then allowed the small ring on the driver side to push through the threads (sounds like it may be plastic?)
Taking it to the shop Monday that he bought it from last year to hopefully get it fixed under warranty.
Do y’all think my diagnosis is correct? What causes something like that to happen? He hasn’t done any work on it. I saw there are some known issues with the t47a in Cervelo’s but haven’t seen this specifically called out.
Edit: After more research it turns out the video I watched was an after market replacement that presses through the drive side. I guess the factory bb driver side is really just an external t47 and as someone said the flange broke.
by SpaceOlympix3022
1 Comment
The stock BB, in combination with the heavy chamfer of the BB shell means that it’s easy for the BB flange to break off and it allows the BB to thread itself into the frame. It’s something that is somewhat known. Unthread the BB, and replace it with an aftermarket one with a larger and thicker flange. The Wolftooth one is a good option. Should solve your problem.