Originally Posted by
Papa Tom
Explain?
Bottom line: Is a 68mm BB going to solve this problem? Having surveyed this forum and a bicycle mechanics forum on FB, I think it might. I will let you know when I install the new one that's coming (hopefully) by the weekend.
Thank you all.
If you're installing a 73 in a 68mm shell, then yes, definitely. Sounds pretty clear that you just have a bearing that's too wide for your shell. The 68 on order should install fine, no problem.
And your old BB left cup may not be the same ID as the new one. I found the old UN71's and 91's are a smaller diameter, so an old cup from them will not slide over the UN55 BB cylinder and seat properly. So unless you have calipers, don't try to mix and match cups from different vintages. If the UN55 left cup won't go in all the way (sticks out 5mm), then it's obviously a shell width issue.
Just put a metric ruler up to your shell and measure it so there isn't any more question (although I think the question has been more than answered).