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My problem is that my squared taper crank arm keeps on coming loose no matter how hard I tighten the bolt - it also starts creaking.

Here’s a video of the problem

https://giphy.com/gifs/RlN0wNSZsWluF5izKz

I’m thinking replacing the crank arm would do it since it seems to have become larger than the axle. But I’m curious: can this be fixed somehow?

Edit: I’m thinking the whobbliness is normal since the bolt is suppose to tighten it against the axle. But the problem is that the axle has come all the way through the space for the arm, making it impossible for the nut to squeeze it against the axle.

Here you can see the axle coming all the way through the arm. Is this normal? Shouldn’t it stay inside so the nut can squeeze it against the axle?

enter image description here

Ideas if this can be fixed? I’m thinking that a new axle could also have the same issue

Edit 2: I’m thinking perhaps a washer that is as big as the crank hole walls could push towards the axle?

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    Does this answer your question? Loose crank arm – Argenti Apparatus Sep 14 at 17:39
  • The lower left edge is already widened and destroyed. – Carel Sep 14 at 18:00
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    The question that comes after "Can you" is "Should you" - given the issues of safety, and the cost of a used square taper, non-drive side crank arm, that answer is "Probably not" . Visiting you local bike coop, LBS for a used crank, or visit your recycle center and find a donor bike. All above will cost less time and provide a more long term and reliable fix than any 'fix' can hope to achieve. – mattnz Sep 14 at 22:02
  • Regarding your washer idea. You will put more torque on the crank arm than you can on a bolt. What will happen is the crank will spin tiny amounts with every pedal and will eventually come loose anyway. There is no fix that is more cost effective than to replace. – abdnChap Sep 15 at 9:14
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This question about loose crank arms has been asked and answered several times before on this site, but yours is the worst I've ever seen I think.

Unfortunately your crank arm is ruined. If the alloy crank gets loose and is ridden on the hard steel spindle wallows out the relatively soft alloy. It does not matter how tight the retaining bolt is done up the deformed crank arm will continue to come loose.

Replacement crank arm (or both crank arms) is the only solution. The bottom bracket and spindle are probably fine (unless the bearings are worn out).

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  • Thanks! MY question was more for the ingenious "can it be fixed". I know that a new crank would be the best thing (since the other arm works fine). But I suppose there really isn't a fix? I heard about cutting aluminum cans and fitting layers in the space between the arm and the axle – Luca Matteis Sep 14 at 19:22
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    @LucaMatteis the square taper surfaces in the crank arm need to be completely flat to mate to the surfaces on the spindle. If the surfaces are not flat the arm will rock under pedaling forces and come loose. Shims are not going to fix that. – Argenti Apparatus Sep 14 at 19:59
  • @ArgentiApparatus - If I had this problem I'd definitely consider giving the aluminum can pieces a try. The classical can design has thicker and thinner spots, and it should be possible to cut pieces that are effectively wedge shaped to eliminate the tendency to rock. – Daniel R Hicks Sep 14 at 21:42
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If the bolt is bottoming out on the spindle, then tightening the bolt won't do anything. As you pointed out, you could potentially insert the correct spacer, if you could find one, into the crank to allow the bolt to tighten once again. It would be a rather special spacer though.

If you are truly without scruples (i.e. if it's a junk bike and you need to either fix it or scrap it) you could grind off a couple millimeters of the crank spindle, which would do the same thing.

If you rode the bike with the crank arm loose for any length of time, the crank arm is probably ruined and you will need another crank arm anyway. It's probably best to buy or scrounge a new left crank arm.

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  • Worse, a wobbly crank arm hardens the square taper to a glass-like state and snaps it away, leaving a razor-sharp edge that is sure to cut into the rider's calf. – Carel Sep 14 at 17:58
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    Shortening the spindle will just accelerate the problem as there is now less surface area to distribute the load over – Argenti Apparatus Sep 14 at 19:59
  • A left crank of correct type and length and in an acceptable state is probably not so hard to find. – Carel Sep 15 at 7:34
  • Ye trusty local bike store will probably have a ton of used crank arms that can be had for little money, probably less than 20$ apiece. For a beater bike this is definitely an option. – arne Sep 15 at 12:06

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