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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 10-14-09, 06:04 PM   #1
Joe_Mo
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Busted Bottom Bracket

I was tightening my bottom bracket just a few minutes ago and I'm pretty sure I broke it. I've tightened my BB a few times before and this has never happened. Is this going to cost me a fortune? what kind of questions should I ask my LBS if I have to replace the whole thing?

The bike is an old GT Force

and most importantly, can I still ride tomorrow?
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Old 10-14-09, 06:28 PM   #2
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Depends in part on whether what you picture is chipped teeth on the spline with the ring
intact or a full width crack of the spline ring. Full width crack means the ring won't stay
very tight and there is a risk of the BB loosening up and shifting position. Not fatal but
not good either. Loktite would serve as a temporizing measure, but you would have to
completely degrease the threads. Whereas getting a separate ring is unlikely, the BB
assembly is not that expensive. You might find a packrat who kept an old BB and liberate
the ring. If you just chipped off a couple of teeth, this is not significant. There is fairly
substantial metal left, for the function the ring serves.
Sample replacement: http://www.nashbar.com/bikes/Product..._200276_200423

The old BB I have has a metal ring, but the newer ones appear plastic.

Last edited by sch; 10-14-09 at 06:32 PM.
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Old 10-14-09, 06:29 PM   #3
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Hello I would ride it for a day or two. you should be able to find a replacement part at your bikeshop. that is the plactic 'adjusting' cup right?
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Old 10-14-09, 06:36 PM   #4
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Originally Posted by Bianchigirll View Post
Hello I would ride it for a day or two. you should be able to find a replacement part at your bikeshop. that is the plactic 'adjusting' cup right?
It looks like it. I'll check in the dumpsters behind my LBS to see if any BB parts were thrown out or if they have any spares, before trying to buy a new BB.
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Old 10-14-09, 06:39 PM   #5
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A new square taper BB can be had for $25 if you shop around. Your LBS may have one in the correct size but will likely be $35-40. If you have your own BB tool you can replace it no problem.

In any case this looks to be the non-drive side plastic retaining ring. The only purpose it really serves is to prevent the BB from torquing fore/aft or vertically, not laterally. The drive side is metal and is welded to the BB, the drive side holds it in place and the non drive side is effectively just a shim to keep it from torquing as you pedal. As long as it is still threaded in and the plastic completely surrounds the cartridge you will be fine to ride it tomorrow, but replace it when you can. Theoretically you dont really need the ring(on a steel frame) unless you are heavier than about 140lbs.

Also because it doesn't serve to hold the BB in place or prevent axle from having lateral wiggle this plastic retaining ring doesnt need to be "tightened" it should just be snuggly against the BB shell on the frame. It is made of plastic because it doesn't need to withstand any serious forces. Don't tighten it so much next time.
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Old 10-15-09, 01:48 PM   #6
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this looks to be the non-drive side plastic retaining ring.
If it is it really doesn't need to be replaced. Just ride it.
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