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?