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Old 06-18-08, 06:59 AM   #1
indianatrails
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Bottom bracket keeps coming loose

...and it has only ~1000 miles on it. I've tightened it a few times (both sides). Should I just replace it? It's a Shimano, square taper 68x11?, on a Bianchi Bergamo (hybrid). The drive (right) side seems to be coming loose most often, which threads in reverse (lefty tighty). Could there just be too much friction within it, putting torque on the drive side threads as I pedal? Thanks in advance!
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Old 06-18-08, 07:14 AM   #2
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What have you been tightening it with?

The torque spec for Shimano cartridge bottom brackets is around 30 lb/ft. Imagine a 30 lb weight hanging off of the end of a foot long wrench handle. That's more than I'd probably use if simply left to my own devices. If it was my bike I think that I'd remove the bottom bracket completely, grease the threads and reinstall it tightly.

If anything, pedaling procession should actually tighten the bottom bracket within it's shell.
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Old 06-18-08, 07:41 AM   #3
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Originally Posted by Retro Grouch View Post
What have you been tightening it with?

The torque spec for Shimano cartridge bottom brackets is around 30 lb/ft. Imagine a 30 lb weight hanging off of the end of a foot long wrench handle. That's more than I'd probably use if simply left to my own devices. If it was my bike I think that I'd remove the bottom bracket completely, grease the threads and reinstall it tightly.

.
+1 proper torque is your friend. To get that 30lb-ft of torque, I'm typically using an automotive type of torque wrench, 1/2" socket, 15" handle length. It's more than most people imagine.
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Old 06-18-08, 07:44 AM   #4
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I borrowed a Park BB tool and gave it a crank (that was some terrific imagery for torque, by the way, thanks!) Been meaning to get a torque wrench, so if it loosens again, there's my excuse. I'll take your advice and set to 30lb/ft. If precession wasn't the cause of the loosening, I'm still trying to understand what's up with it.
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Old 06-18-08, 06:53 PM   #5
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Properly greased and torqued bb's should not come loose.
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