Should I reinstall a fixed cup that came loose?
 

On Sheldon Brown's site mentioned in the post above, I read that an old fixed cup shouldn't be reinstalled in one's bottom bracket after being removed. But why not? The fixed cup on my bike came (1984 Trek 560) loose recently so I removed it the rest of the way. I suspect that some water eventually penetrated the BB this winter and contaminated the grease, after which it loosened gradually? In any case, after cleaning the cup and BB shell as best I can, I can't identify any damage except a slight rustiness on the outermost few threads of the shell on the fixed cup side. Is there any reason I can't just reinstall the same cup? If yes, why not? If no, are there precautions to take or techniques to follow when reinstalling? I was thinking of greasing the threads and perhaps gently using the bench vise removal technique in reverse.

Thanks for your advice!

there is no reasons why you can not reinstalled a fix cup, unless there a problem with it. do use plumber tape or grease on the treads of the cup. do bring it up to torque .use new bearing & grease. I alway remove & reinstalled my fix cup as part of overhaul my bb. good luck.

You misunderstand. His point is that you don't *really* need to remove the fixed cup during a normal bb overhaul. I'd say it's wise to do this IF you are going to the trouble of repacking the bb anyways. Good preventative measure against seizing.

The only reason your fixed cup came loose is because it was installed with inadequate torque, not because the grease was contimnated. If the grease was contimnated/washed out then you'd have a seized bb, not one that is backing out.

All you need to do is clean the BB shell and the fixed cup as best you can, use loads of grease and re-torque to spec. If you're going to all this trouble, you might as well put in a $20 shimano cartridge bb which will last years and require no mainteanece.

Thanks for the encouragement and for setting me straight on the meaning of Sheldon Brown's tip. I've reinstalled the fixed cup for now (without torque wrench, just using a bench vise and the frame), and will probably go for a cartridge bottom bracket in the near future.