Bottom bracket feels rough ... for a while
 

I've been having a weird intermittent problem with the BB on my bike that has persisted despite putting in a brand new BB.

Before I go into (long-winded) detail, here's a quick executive summary of the problem:

UN54 BB feels rough and binds, then corrects itself and is smooth for a few hundred miles, then gets rough again. Have seen this on two different BB's (UN54, UN55) on same frame and crank. Brand new UN55 is doing the same thing.


Originally, I built up the frame (Soma Double Cross Disc) with a Sugino XD600 crank and Shimano UN54 113mm BB that I moved over from my previous bike. I should also note that the BB shell was faced and chased before assembly. This combo ran fine for a couple of years. Then one day late last year I was prepping the bike for a ride and noticed a rumbling noise and feeling when I turned the cranks. I removed the chain and verified that nothing was rubbing (e.g. the FD) but the rumble persisted and the spindle would occasionally bind. Not really a gritty feeling like sand, but more like the way bearings feel when they're too tight.

So I figured, okay this older BB has probably had it, and I ordered a new UN55. Here's where it starts to get strange.

When the new BB came I removed the old one, and was surprised to see that the spindle felt buttery smooth when I turned it with my fingers. So I figured, maybe I had it torqued too tight or something. I went ahead and put the UN55 in anyway. I torqued the drive side to spec, but then went a little easy on the NDS cup, maybe 30 ft-lb instead of ~50, just to avoid any excess compression on the cartridge bearings. This brand new BB was fine for maybe 50 miles, then on my second or third ride, I noticed the rumble happening again a few miles into the ride. Out of puzzlement, I figured I would just keep going. That way, if something broke at least the root problem would finally reveal itself. But the rumble just kind of went away. I didn't really feel any kind of shift or pop in the bearings so I don't know the exact moment when it happened.

After that, the new BB was smooth for maybe 200 miles. Now this morning I was lubing the chain, and I noticed it's happening again.

Does anyone have any ideas? Is it possible for the BB spindle to shift somehow in a way that binds the bearings, then pops back in like a dislocated shoulder? I've been riding in fairly sandy/salty conditions this year, but this is a brand new BB, and the old BB had the same problem last fall in much cleaner conditions.

Despite the fact the bottom bracket shell was faced when you got the bike, I'd have it checked again. Something there isn't right.

I've got one older bike where the threads on each side are obviously not machined concentric to each other.
Even after facing, if I tighten the NDS cup all the way, it binds the cartridge BB. I tighten it to where I can feel it binding and then back off until I can't feel it.