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Bottom bracket feels rough ... for a while

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Bottom bracket feels rough ... for a while

Old 02-25-17, 08:45 AM
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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.
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Old 02-25-17, 08:48 AM
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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.
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Old 02-25-17, 09:05 AM
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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.
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