Why Is My Crank Arm Keep Coming Loose

You need a new crank. Try putting them on more firmly by pressing the opposite side of the BB to which you are putting the crank on up against a post or anything solid to give it a solid backing then bash the crank arm onto the BB as hard as you can with a rubber mallet.

Crank Arm Issue Emtb Forums

Surprised its not an interference fit the crank arm it comes right off.

Why is my crank arm keep coming loose. So heres the deal truvativ cannot manufacture their splines properly resulting in your cranks coming loose. Re-torqueing the bolt will keep the arm on for a short amount of time but eventually will critically damage the crank arm bolt. If you use these or the equallivant for your make you can tighten your crank bolts and then screw these on.

Aluminum is softer than steel so if the interface is loose at all you start rounding out the opening for the spindle. You can try locktite but Ive had no success with that either. Youre right about the preload bolt.

Blue Loctite but in a pinch any kind of glue works on the threads. Tapers should be greased. At some point the crank has become loose and the splines on the crank and the spindle may have worn away at each other.

As someone pointed out above with a newly fitted crank it will bed in and needs regular tightening for a few days. Make sure the cranks are on the spindle evenly and are on the spindle enough but also not sticking out to where tightening them doesnt do anything. It doesnt have to do with quality.

Thats because the spindle the axle the crankarms spin on is made of steel and the arms are aluminum. -if your crank arm isnt on the spindle enough or too much it can come loose you want the arm to be at least 34 the way on the spindle but not on so much that the spindle pushes through the other side bottoms out. Check both crank arms for tightness.

If your cranks are square taper once youve had them come loose youll have dammaged the taper and they will keep coming loose. LOCTITE 648 on the square taper is even better than grease. Loc tite may work for a while but it will not continue to work for more then about 1.

It could also be a problem with your bottom bracket but it would have to be really worn out to cause the crank arms to loosen. Im not sure if theyre screwed yet if you havent done anything particularly harsh to them while theyre loose they shouldnt be too damaged. It seems like a design issue and Im not sure how to fix it.

Torque specifications vary from 30 to 60 Nm. You will have no choice but to replace it. All cranks will do this.

It does NOT hold the crank on by any means. This is classic sign of a bad crank arm. I say may because there is.

The first time it worked loose the harder BB axle deformed the crank slightly which means that youll never be able to get it to stay. For 8 spline cranks you can usually see through the pinch bolts slit where they are. Cant guarantee but this is what bad cranks do.

If theyre square taper then the left hand crank is knackered. When the crank arm is loose and you pedal with it you damage the four corners of its socket that rest in the axle. If youve been repeatedly riding with a loose crank arm it could be that its now damaged.

Depending on your crankset one crank arm is usually attached to a spindle that goes through the bottom bracket. When you fail to tighten its crank bolt sufficiently an arm can come loose at which point it wobbles the hard steel spindle enlarges its hole in soft aluminum and the parts no longer fit correctly. Its only purpose is to preload the crank so it can be tight enough before you do the main arm bolts.

A retaining compound eg. Somehow this damage causes the crank arm to wiggle enough to unscrew the nut little by little until it just falls off again. If the arm is damaged no matter how tight the bolt is torqued it will not stay tight on the spindle.

The splines on the crank arm can be ovalized or otherwise damaged if ridden when loose. You could try tightening with lots of torque grease on the square taper and threadlocker eg. And if you are able to tighten it down without it slipping no big reason to think the threads on the spindle or nut are the problem.

Best bet is to have the left hand arm replaced. Since they dont sit solid on the spindle.

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