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A few weeks ago I bought a new (albeit cheap) self assembly bike from a local store, this bike to be exact http://tinyurl.com/gw77p9t . After about two weeks use (one and a half hours of cycling on pavement five days a week) the left crank started to creak, came loose and eventually fell off. I cleaned the crank and applied new grease which stopped the creaking and prevented it from falling off but the crank still came loose so as to make cycling uncomfortable. I then bought a new crank arm (this crank arm http://tinyurl.com/zz3mjzr ), took off the old crank, cleaned and greased again only to find the same problem. I can't imagine what else the problem could be, any suggestions?

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    Did you tighten the crank enough? If you don't have a torque wrench, the correct torque is really tight. If it doesn't feel like something is about to give, you are doing it wrong. – ojs May 8 '16 at 17:18
  • I tightened it as much as physically possible without breaking my arm. – Moses May 8 '16 at 17:22
  • It sounds like you need a longer wrench. – ojs May 8 '16 at 17:26
  • Would that be a problem? The handle on the wrench I'm using is about 15-20 cm long (I'm trying to estimate from memory). – Moses May 8 '16 at 17:28
  • Too short wrench. You need something about 40cm length, and yet you need much power to tighten it well. And as Batman answered, you probably damaged the BB spindle. – Alexander May 8 '16 at 17:45
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A loose crank arm can damage both the bottom bracket and the crank arms. In your case, since you've run the crank arm til it fell off the bike, it is likely you ruined the bottom bracket. If your crank arm is loose, immediately stop and tighten it.

You will need to likely get a new bottom bracket and possibly yet another new crank arm. Replacing a bottom bracket requires a special tool (bottom bracket tool) and a compatible bottom bracket (which will typically be marked on the bottom bracket itself). You may want to leave this job to a bike shop.

  • If you replace the BB, consider to take a cheap sealed bearings. It will not cost much more, but will last much longer. – Alexander May 8 '16 at 17:48
  • What are sealed bearings and what is their function (this is my first bike and I'm still learning)? – Moses May 8 '16 at 18:05
  • Its basically the modern bottom bracket. If you go to a bike shop, its what they'll install. Cheaper bikes use an older style. – Batman May 8 '16 at 18:11

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