Bottom bracket getting loose
09-28-20, 02:02 AM
#1
Senior Member
Thread Starter
Bottom bracket getting loose
I have an old bike that I use to get around town and I've been having a strange issue with it: the bottom bracket keeps getting loose. It's a threaded square taper BB.
I disassemble the cranks, tighten it, and after less than an hour of riding, I start to feel play in the cranks. When I disassemble it to check what's wrong, I always find the right side of the BB completely loose.
The threads on the BB and frame are ok, and I've tried with threadlock without success.
Any idea?
I disassemble the cranks, tighten it, and after less than an hour of riding, I start to feel play in the cranks. When I disassemble it to check what's wrong, I always find the right side of the BB completely loose.
The threads on the BB and frame are ok, and I've tried with threadlock without success.
Any idea?
09-28-20, 06:32 AM
#2
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To what torque value are you tightening it? Shimano cartridge bottom brackets are specified at 36-50ft-lb which is surprisingly high when going by feel.
09-28-20, 08:28 AM
#3
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Cartridge or cup-and-cone bottom bracket?
What thread spec is the bottom bracket?
What tools are you using to tighten the loose parts?
What thread spec is the bottom bracket?
What tools are you using to tighten the loose parts?
09-28-20, 08:52 AM
#4
Really Old Senior Member
Is it a RH or LH thread?
09-28-20, 11:43 AM
#5
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Thread Starter
It's a cartridge type. English thread. I don't have a big enough torque wrench, but I tightened it width a spanner that's 50cm long and torqued it more than I felt comfortable with.
09-28-20, 11:59 AM
#6
Really Old Senior Member
Put a wrap or 2 of Teflon plumbers tape on it.
09-28-20, 02:08 PM
#7
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I suspect the threads in the shell are damaged or were cut oversize by a worn tap. @Bill Kapaun's suggestion above may help. Failing that, a threadless cartridge may be the fix.
09-28-20, 02:28 PM
#8
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It's terribly passe', but if there's a half decent bike shop near you they can check the threads and tighten the BB properly. It's not terribly expensive, IME.
Just out of curiosity, did someone work on the BB shortly before this unscrewing problem started?
Just out of curiosity, did someone work on the BB shortly before this unscrewing problem started?
09-29-20, 12:11 AM
#9
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Thread Starter
The threads are OK. No one but me works on my bikes. I've been doing my own mechanics for 20 years. Never had a BB do this, and I've replaced quite a few.
09-29-20, 12:11 AM
#10
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09-29-20, 05:14 AM
#11
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I wonder if the BB face needs to be resurfaced? Having it nice and square can only help.
10-16-20, 04:38 AM
#12
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Thread Starter
Well... I think I finally managed to solve it. I put so much threadlocker on it I'm not sure I'll be able to remove it if needed. It has stayed in place for 2h, which is a record.
Just hoping I don't need to remove it soon
And no... I tried and it got finger loose with a normal amount of threadlocker.
Just hoping I don't need to remove it soon
And no... I tried and it got finger loose with a normal amount of threadlocker.
10-17-20, 09:32 AM
#13
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Another possibility is an oval BB shell. My son bought a new bike, and the BB kept coming loose no matter how tight you made it. The bike shop was not of much help, but I insisted the mfg rep be called in. I showed the rep that the BB shell was oval up and down, and he was amazed I found that. He gave us a new frame.
