i have this recurring problem with a cup and cone bb: it keeps coming loose. now, i've opened and re-greased this bb a number of times in the past without problem, but ever since my last re-grease the bb can't stay tight. since then i've had to re-tighten it about once every couple of days -- i tighten it up on the adjustable side until there's no play on either crank arm but then, within 30 or 40km of moderate riding it starts to loosen again.

any ideas?

First off, english or italian shell and what type of bb? If your using a cup and cone, with a lockring, yeah, you've really got to get a good purchase on that lockring and crank it, while at the same time keeping the cup from threading in with it. If this is what your doing, and it's not working, sounds to me like you should probably have your bb shell faced to ensure the fixed cup and the lockring are truly flat and tight against the surface. Another thing to check is making sure you don't have a crack in your frame or the adjustable cup of the bb.

right, i should have mentioned that it's not italian. whoever thought that concept up in the first place i wonder?

when i tighten it, i take the pin pliers and tighten the adjustable cup until there is no play, keeping the lock ring a turn or so from tight. then i hold the cup steady with the pin pliers and reef that lock ring on with a lockring wrench. there's always some slippage with the pin pliers, though, so it usually takes three or four tries until it's "right", but i assume that's normal.

i'm planning on re-inspecting the fixed cup tonight. i did take it off on my last re-grease, but i'm pretty sure i put that sucker on tight. will check for facing.

Sounds like you're doing everything right. Possibly use teflon tape instead of grease on the threads? Use a lot. Failing that, I might be persuaded to go to blue loctite.

Is this on a fixed gear? I couldn't make my fixed cup stay on my track bike. Moved to a cartridge.

coincidentally, it is. but i'm far from a masher and rarely ever do any of those high-stress maneovers that fg's are known for.

The same BB I had on a SS bike wouldn't stay put once I went to fixed. I think it has something to do with the tension on the chain and the additional stress of tension in both directions but don't quote me on it. My knowledge is purely anecdotal.