Originally Posted by
Grand Bois
I don't think you could get the tap started crooked even if you tried really hard. It threads right in and just removes a little bit of material. Fourteen millimeters and 9/16" are very close. You don't need special cutting oil for this. Any oil will do. In fact, no oil at all will do.
I'm afraid you're wrong there, old boy. I managed to do exactly that on a 1950s NOS Stronglight 49D. The crank side worked fine. I still regret it. The local engineering shop says they can repair it for $60 but I'm hesitating...