Over-tightening a BB

Question

I just installed an external bottom bracket (Hollowtech II type) on my steel bike. The manufacturer (Sugino) prescribes a 40-50Nm torque. I own no torque wrench, so I just wrenched it on pretty tight. Later on I came to bright idea to stand on a scale whilst I pull the wrench, and compute from this the exerted torque. Turn's out I've put a bit more than 50Nm on the cups, not sure how much more though. Would it be fine to leave it this way, or should I loosen the cups and redo the installation?

In other words, can over-tightening an external bottom bracket do harm?

Answer 1

I don't think anyone uses a torque wrench for installing the cups. If you did any damage, it would be to the threads of the BB or to the threads on the frame. However, unless you were an ogre when you tightened it down or you cross-threaded it, I doubt you did any damage. I do hope you used grease/anti-seize though, since you may ruin the threads if you didn't. You could also have damaged the spacers for the BB, I suppose, but it'd have to be pretty mangled if it affected the chainline and Q-factor significantly. So, if its this which you're worried about, I'd just leave it. Given that you have a Sugino crank, I'm assuming you probably don't have spacers.

When you're installing the crank, theres a cap you have to put on -- this only requires something like 0.5 Nm. If you overdo this, you'll load the bearings such that they wear down faster. If you've overtightened this, you need to undo it. Same with putting the non-drive side crank arm (which is something like 15 Nm normally).