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Fix a bottom bracket that loosens the pedal

My bike started recently having a problem where every few hundred meters my pedal arm gets loose and shaky, and I have to stop and tighten again.

I've completely opened and cleaned the bottom bracket and I've replaced the ball bearings (not the cages). The situation has improved, but the pedal still gets loose.

I'm not sure what to try next in order to fix it:
When I replaced the bottom bracket it seemed not too worn out, and only the point where the ball bearings touch on it had lost the paint, and it had signs of fatigue where the crank arm is.

Any clues? here's a picture of the part:


thank you in advance,
How would you think that the BB bearing would have anything to do with the crank arm (not pedal) loosening? The problem is that once the crank arm is ridden loose it wears the square taper where it fits on the spindle, as the crank is aluminum and the BB spindle is steel. You need a new left crank arm, and then make sure both crank and are kept properly tightened.
Hello Cny-man,

Thank you for your opinion, I showed the bike to a bike shop clerk, and he thought that the crank is not in aluminium. so he said that that's probably not the issue here.

But somewhere there is an issue.

I thought it was the BB bearings because when I pedal, pushing on the left side the bike makes a "creacky" sound. and indeed the bearings I replaced were quite dented. Now with the new bearings the sound seems gone.

Given this do you still think I should replace the crank arm?

also: In your answer I think there was a word missing when you say:

"make sure both crank and are kept properly tightened".

I'm not sure needs to be tightened, crank and ...?

thank you.

.. both crank ARMS are kept... Even steel arms can be damaged when ridden loose. Bearings have NOTHING to do with the crank arms. Either the crank or the spindle are worn, and the "mechanic" should have inspected the parts.
10-4 to what NY said. Examine the crank carefully see if it has any l/r play in it and if it turns smoothly. Take the arm off and examine the crank for wear than examine the arm hole. Any rounding will result in the arm loosening up . Make sure to tighten all well, but not as hard as you can, as you can strip threads.
Never Give Up!!!
Looseness from the bearings and looseness from the crank arm can feel the same to the untrained hand so it's not surprising you weren't sure which was causing the issues. You may very well have had both problems.

If tightening the black nut that holds the crank arm onto the bottom bracket spindle (axle) makes the looseness go away, then the problem is definitely not the bearings themselves.

The creaking you describe is also very typical of a damaged crank arm that keeps loosening up, so signs are all pointing to needing a new crank arm. However, just to be thorough...if the threads on the spindle or nut are damaged, it is possible you are never really getting this tight and that is why is loosens. But if you can take a wrench, crank that nut down solid and it doesn't feel stripped or anything, and the cranks still gets loose, probably a bad crank arm.

Note finally that if it is not loosening up now, but is still creaking, you might also remove the pedals, grease the threads, and reinstall them. That joint can make similar creaking sounds.
Hi I have this problem and I am 99% certain when replacingt he left crank arm I incorrectly threaded the crank bolt. This has resulted in the threads on the nut and spindle being worn.

My question is, what do I need to replace?

Do I need an entire crankset/chainset or can I get away with just a bottom bracket?

(08-11-2014, 11:11 AM)Big Dave Wrote:  Hi I have this problem and I am 99% certain when replacingt he left crank arm I incorrectly threaded the crank bolt. This has resulted in the threads on the nut and spindle being worn.

My question is, what do I need to replace?

Do I need an entire crankset/chainset or can I get away with just a bottom bracket?


Bottom bracket and nuts or bolts depending on what the new BB requires - if like most Shimano, they are not provided with the BB.
If the threads on the spindle are damaged enough then of course you will have to replace the spindle. If the crank arm has come off more than once the odds are very high that it must be replaced as well, even if that was not the original problem. Once you are replacing both spindle and arm it may be best to replace the whole crankset if the bike is worth it. If you replace only the spindle you must be careful to get a spindle/BB that is compatible with the type, taper and style of crank.
Thanks. Want to make sure I don't get ripped off. Someone suggested replacing the BB, crankset, rear crank and chain too, so as to ensure even wear.
The rear is called the cassette, and the cassette and chain have nothing to do with your original problem. You do not have to replace chain and cassette when you replace the front chainwheels. You should check the chain for wear and replace the cassette only if necessary. http://sheldonbrown.com/chains.html

Most importantly, you need to make sure the money you spend make sense in light of the bike involved.
Just get a new BB and crank arm, problem solved.
Already suggested, and again the OP needs to make sure to get a compatible BB/spindle.

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