Originally Posted by
Ozpedal
I am restoring a 1980s Zeus and after much research, purchased a NOS French-threaded Zeus BB off good-old EBay. And it doesn't fit! The cups won't even start, I.e the cups are larger than the shell.
English/ISO cups are slightly smaller diameter than metric (French/Swiss) thread cups.
Further investigation suggested the shell is probably British standard (or ISO if you prefer). So I did what any normal person would do BEFORE parting with their cash and tried a Shimano hollowtech cup I had lying around in the garage...and it fitted perfectly! The problem I have now is because my Zeus shell is right-hand threaded on both sides, I can't simply purchase ISO cups because one will be left-hand and the other right hand.
No standard English/ISO bottom bracket came with right-hand thread fixed cups, so either you're mistaken, or a previous owner cross-threaded the fixed cup side. You seem to know what you're doing so I'll assume that the shell may have been cross-threaded.
If the threads aren't too badly damaged, you could, as CliffordK suggests, use an adjustable cup on each side. If the cup doesn't seem secure in the damaged threads, you could use a threadless cartridge, such as is available from Velo-Orange and others, or ream and tap the shell for Italian thread and use Italian thread cups with a spindle for a 68mm shell to get the proper chain line.