You didn't mention what type of frame you're working on. If it is some sort of older French bike that would normally have a French BB, then everything kinda makes sense. It might be that you pulled out a tight-fitting French cup and then "cleaned up" the shell with an English tap. At that point it would stand to reason the the new, English cup would fit, while the original French cup would not. The English cup is 1.370" in diameter with 24 tpi. The French cup is 35mm with 1mm thread pitch. Assuming that the nominal sizes are close to actual sizes: The English BB is 0.20mm smaller in diameter which would fit loosely in a shell previously cut to 35mm; the French thread is finer than the English 25.4 tpi (1mm pitch) vs. 24 tpi and would bind in an English shell. So, perhaps this bike is now Franglais (speaking French, mais weeth un ree-dic-u-luze ax-cent.)
Also note that some cups are bigger (or smaller) than the nominal size (especially cheap ones) and may bind in a cleanly threaded shell. Also, there are some wierdo sizes out there that can cause problems. 26tpi cups on some older English bikes come to mind. Note too that some "French" threaded bikes have left hand threads on the drive side. These are actually called Swiss threaded.
> Yesterday one of my mechanics was pulling a bottom
> bracket apart. The
> non-drive side was hard to get out so I chased the
> BB shell and put in a new
> cup and it fit like a champ. Then tried to put the
> old cup in and it got
> half way and started to seize up. Pulled the cup
> back out and checked the
> threads and they looked ok. Then checked the threads
> against the new cup and
> discovered that they were more or less threads per
> inch, dont remember
> which, so I put in a new bottom bracket. The only
> thing I could think that
> could be the problem would be that it was a French
> cup that had been forced
> into the shell. Not having a clue to French BB
> threading I was hoping
> someone here could shed some light on this.
>
> Thanks in advance,
>
> Mark, three new old bikes on the way-you guys and
> gals are a bad influence,
> Poore
>
>
>
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