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I changed the bottom-bracket in my mountain bike two years ago, the problem was that the bolt on the crank on the non-drive side was continuously getting loose, to the point that I had to stop and tighten it again every mile.

With a new BB the bike was all right, and it worked fine for almost two years (I wasn't using it that regularly though). Until last week, when it started having the same problem again.

The BB is a part of the bike that usually lasts forever, so I'm not really convinced about changing it again, because the current one lasted so short, I think there could be some other problem in the bike, that causes the BB to wear faster. But I haven't got a clue about what that could be.

Does anyone have experience or thoughts about it?

thanks,

  • It would be helpful to know specifically what sort/brand of pedal we're referring to here. – Zippy The Pinhead Aug 13 '15 at 15:58
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    By now the crank arm and likely the crank axle are probably "fried" from running loose so much. A loose crank arm is something that must be attended to immediately, not "when I get around to it". – Daniel R Hicks Aug 13 '15 at 16:36
  • @DanielRHicks because if you don't you ruin the cranks and the axle (bottom bracket spindle) beyond repair. – jqning Aug 13 '15 at 20:15
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My guess is that by the time the first bottom bracket (crank axle) was replaced the left side pedal arm was also damaged. When you installed the damaged crank arm to the new axle it worked for awhile. You are now at the point that you have a worn arm and a worn crank axle. Replacement of just one of the components will result the premature failure of the other. You need a new bottom bracket and crankset. As this is an expensive repair it may be worth looking for a used assembly that is in good shape. The crank arm bolt should be tightened to about 30-35 ftlbs of torque. This takes quite a bit of effort with the average 6 inch long allen wrench.

  • Yes, in most cases of the crank arm coming lose the arm is damaged sooner than the axle. Replacing only the axle is kinda dumb. – Daniel R Hicks Aug 14 '15 at 0:43

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