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Old 05-19-17, 02:36 PM   #1
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Why would a square taper BB spontaneously tighten up?

I recently got a new [sic] crank and bottom-bracket. I regressed to square-taper. It is BSA. After about 3 months of very moderate use, I noticed the pre-load needed adjustment; it was a bit too tight. Although I didn't feel any roughness, there was quite a bit of resistance turning the crank, compared to 10 other bikes in the garage (ranging from crap to Campy). I backed the variable cup off about a quarter of a turn, and now it turns more freely, but still with no lateral play. I don't remember it being that way initially when it was installed, and moreover, the lock-ring was not tight (I could move it with just my fingers), so I think something moved since the initial install (which was done professionally).

Everything I know about square taper BB is that the usual concern is that they might get too loose if you don't set the lock-ring properly. After nearly 30 years of malignant neglect, my Italian square taper BB was perfectly fine, never needing adjustment (despite the right-hand thread on the drive side).

So, what would cause a BB to spontaneously tighten, and, more importantly, how can I prevent this from happening again? It is a White Industries BB, fwiw.
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Old 05-19-17, 02:43 PM   #2
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Precession would cause the adjustable cup to tighten just by pedaling.

My guess is that the lock ring wasn't tight enough. If you're really worried about it throw some (a drop or so) blue locktight on the adjustable cup.
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Old 05-19-17, 02:45 PM   #3
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mechanical precession

lockring not set tight enough
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Old 05-19-17, 02:50 PM   #4
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Thanks. That at least is consistent with my observation that the lockring was not set tight enough. I am assuming the precession wouldn't be visually obvious in any way?
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Old 05-19-17, 02:56 PM   #5
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Thanks. That at least is consistent with my observation that the lockring was not set tight enough. I am assuming the precession wouldn't be visually obvious in any way?
...it only becomes obvious when you discover your adjustment has changed. Cheer up, on the French and Italian ones, they work their way out, not in.
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Old 05-19-17, 02:59 PM   #6
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My Italian one was perfect for almost 30 years. Maybe they knew something ...
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Old 05-19-17, 03:22 PM   #7
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Originally Posted by wgscott View Post
I recently got a new [sic] crank and bottom-bracket. I regressed to square-taper. It is BSA. After about 3 months of very moderate use, I noticed the pre-load needed adjustment; it was a bit too tight. Although I didn't feel any roughness, there was quite a bit of resistance turning the crank, compared to 10 other bikes in the garage (ranging from crap to Campy). I backed the variable cup off about a quarter of a turn, and now it turns more freely, but still with no lateral play. I don't remember it being that way initially when it was installed, and moreover, the lock-ring was not tight (I could move it with just my fingers), so I think something moved since the initial install (which was done professionally).

Everything I know about square taper BB is that the usual concern is that they might get too loose if you don't set the lock-ring properly. After nearly 30 years of malignant neglect, my Italian square taper BB was perfectly fine, never needing adjustment (despite the right-hand thread on the drive side).

So, what would cause a BB to spontaneously tighten, and, more importantly, how can I prevent this from happening again? It is a White Industries BB, fwiw.
Not all. Lock ring is pretty stupid. Tighten it properly and it stays there.
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Old 05-19-17, 03:24 PM   #8
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...it only becomes obvious when you discover your adjustment has changed. Cheer up, on the French and Italian ones, they work their way out, not in.
French & Italian adjustable cups are right-hand threaded just like English/ISO cups.

It's the fixed cups, on the drive side of the bike, that are reverse threaded and can work loose on French and Italian bottom brackets.
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Old 05-19-17, 03:45 PM   #9
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My Italian one was perfect for almost 30 years. Maybe they knew something ...
Or maybe it got gummed up enough to not want to move anymore. (The cup, not the bb itself.) That's usually my observation.
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Old 05-19-17, 03:48 PM   #10
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Or maybe it got gummed up enough to not want to move anymore. (The cup, not the bb itself.) That's usually my observation.
I think you are right.

I paid someone at the bike shop $5 to get it off, because I couldn't.
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Old 05-19-17, 03:49 PM   #11
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I'm still having some problems grasping why a lockring would prevent the bb from tightening. I understand how it is supposed to prevent it from unscrewing.
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Old 05-19-17, 04:07 PM   #12
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My Italian one was perfect for almost 30 years. Maybe they knew something ...
...yeah. Once you get past the first few years it kinda sticks itself in there with gunk and junk.
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Old 05-19-17, 04:09 PM   #13
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French & Italian adjustable cups are right-hand threaded just like English/ISO cups.

It's the fixed cups, on the drive side of the bike, that are reverse threaded and can work loose on French and Italian bottom brackets.

...yes. Works its way out and the adjustment changes. What am I missing ?
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Old 05-19-17, 04:19 PM   #14
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Not the OP's case, but I saw a cartridge BB that overtightened with use. It was one of these early Shimano ones, Italian threaded but intended to be threaded from the non drive side with the plastic cup on the drive side. The owner had assembled it backwards and it tightened so much it stuck.
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Old 05-19-17, 04:25 PM   #15
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The lockring does prevent the cup from tightening. As others mention, it's precession, where something spins in the opposite direction of what you expect. Spin a quarter on a tabletop. As the edges spin clockwise, the orientation of the picture on the quarter spins counterclockwise.
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Old 05-19-17, 04:45 PM   #16
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I'm still having some problems grasping why a lockring would prevent the bb from tightening. I understand how it is supposed to prevent it from unscrewing.
The lock ring prevents it from moving. Imagine it has a threaded shaft and two nuts. The shaft is the cup, one nut is the BB shell and the other is the lock ring. If you hold one nut, and tighten the other nut hard against it, the shaft cannot move relative to the nuts in either direction.
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Old 05-19-17, 07:22 PM   #17
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Not the OP's case, but I saw a cartridge BB that overtightened with use. It was one of these early Shimano ones, Italian threaded but intended to be threaded from the non drive side with the plastic cup on the drive side. The owner had assembled it backwards and it tightened so much it stuck.
...Phil Wood warns about this very issue, or at least they used to. There 's a proper direction to mount their BB's.
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