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Bicycle Mechanics Broken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

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Old 08-05-10, 07:58 AM   #1
HMF
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How to make the BB stay put.

Hey all, first post here in this forum.

I have this BB: http://www.treefortbikes.com/product...-73x126mm.html

and all was fine for about 600 miles but then came the knocking sound that indicated it was coming lose. So I took off the crank and tightened it up, and it went away for about another 200 miles, but I'm starting to get the feeling that it's making a comeback.

I Don't have a torque wrench, so I don't know if I'm tightening it "enough", but I can say it's pretty tight. About 200 miles tight I guess. I have an aluminum frame, so I'm afraid to go any harder.

Any ideas on getting this to stick?
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Old 08-05-10, 08:05 AM   #2
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The torque needed to properly install a bottom bracket is far higher than you expect and far more than most people would use if they don't have a torque wrench to guide them. The frame material is not an issue.

BTW, which side is loosening or is it both sides?
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Old 08-05-10, 08:22 AM   #3
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I believe it's the drive side. I think the non-drive side is just a spacer-cup or retainer of sorts to keep the spindle level. It feels very flimsy and could even be plastic.

I just went over to my bike and did a crank-arm test to check for looseness, and sure enough, they wiggle. Time to take off that crank again..
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Old 08-05-10, 08:37 AM   #4
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It is almost impossible to strip a bottom bracket by over tightening. I use wrenches about a foot long, and almost all my strength so it's in excess of 100 foot pounds of torque. On your cartridge BB be sure to use plenty of grease or anti-seize on the inside of the cups where the cartridge sits.

If you feel you've been tightening enough take a moment next time to feel for radial play in the threads before you tighten. This used to be rare, but slightly oversize threads in the BB shell have become more common over the last 10 years or so. If the thread is sloppy the rocking action from pedaling on both sides can start to work things. Solve it with filler in the threads to take up the slop. I use old fashioned fiber dental floss carefully wound around the cup for the full length of the threads and held in place with a film of grease. Then I force the cup in and it stays until I remove it.
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Old 08-06-10, 08:32 PM   #5
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I just want to say thanks for the advice. I took off the crank and really put my weight into tightening that BB. No, it didn't strip, thank God. I stopped trying to tighten it when my hex wrench started bending under the force ( could just see the handle breaking off and the remaining end going into my forearm). Now all I have to do is ride her! Yes!!
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Old 08-07-10, 06:44 AM   #6
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Not a good idea to use a hundred foot pounds (135Nm) rather than follow the instructions that say to use 35-70Nm, depending on the brand and model? Campy outboard cups only need 35Nm.
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Old 08-07-10, 10:23 AM   #7
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Quote:
Originally Posted by DaveSSS View Post
Not a good idea to use a hundred foot pounds (135Nm) rather than follow the instructions that say to use 35-70Nm, depending on the brand and model? Campy outboard cups only need 35Nm.
That's correct and the recommended torque is what you say but it's a LOT higher than most would apply without some experience and/or a torque wrench for guidance.

I think FBinNY's example was to show that even torque well above the recommended level won't strip a bottom bracket shell or the cups.
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Old 08-07-10, 03:19 PM   #8
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My suggestion was based on steel cups which cannot be harmed by over torquing (first side in). The second cup needs far less torque and specs must be followed to avoid compressing the cartridge. Alloy cup shouldn't be torqued as hard because of the risk of the flange cracking, so more care must be given to following a factory torque value even for the first cup in.

Campy specifies lower torque, but their cups are alloy and have an area treated with a traction compound to prevent loosening. I ran Campy's east coast service center in the years that followed the change form the loose ball cups to the cartridge on Record. I can't tell you how many old school mechanics cracked the flange off the right cup until they made the adjustment.
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Old 08-07-10, 08:54 PM   #9
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FB, it's great to have you here.
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