Why Is My Crank Arm Keep Coming Loose

It doesnt have to do with quality. The splines on the crank arm can be ovalized or otherwise damaged if ridden when loose.

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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.

Why is my crank arm keep coming loose. It does NOT hold the crank on by any means. If you use these or the equallivant for your make you can tighten your crank bolts and then screw these on. 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.

This is classic sign of a bad crank arm. Its only purpose is to preload the crank so it can be tight enough before you do the main arm bolts. -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.

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. Depending on your crankset one crank arm is usually attached to a spindle that goes through the bottom bracket.

Loc tite may work for a while but it will not continue to work for more then about 1. Check both crank arms for tightness. Blue Loctite but in a pinch any kind of glue works on the threads.

Torque specifications vary from 30 to 60 Nm. 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. Cant guarantee but this is what bad cranks do.

Re-torqueing the bolt will keep the arm on for a short amount of time but eventually will critically damage the crank arm bolt. All cranks will do this. So heres the deal truvativ cannot manufacture their splines properly resulting in your cranks coming loose.

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. As someone pointed out above with a newly fitted crank it will bed in and needs regular tightening for a few days. You can try locktite but Ive had no success with that either.

Aluminum is softer than steel so if the interface is loose at all you start rounding out the opening for the spindle. If the arm is damaged no matter how tight the bolt is torqued it will not stay tight on the spindle. Since they dont sit solid on the spindle.

If youve been repeatedly riding with a loose crank arm it could be that its now damaged. For 8 spline cranks you can usually see through the pinch bolts slit where they are. When the crank arm is loose and you pedal with it you damage the four corners of its socket that rest in the axle.

LOCTITE 648 on the square taper is even better than grease. Surprised its not an interference fit the crank arm it comes right off. You need a new crank.

Best bet is to have the left hand arm replaced. It seems like a design issue and Im not sure how to fix it. Somehow this damage causes the crank arm to wiggle enough to unscrew the nut little by little until it just falls off again.

If theyre square taper then the left hand crank is knackered. You will have no choice but to replace it. Tapers should be greased.

Thats because the spindle the axle the crankarms spin on is made of steel and the arms are aluminum. A retaining compound eg. You could try tightening with lots of torque grease on the square taper and threadlocker eg.

Im not sure if theyre screwed yet if you havent done anything particularly harsh to them while theyre loose they shouldnt be too damaged. Youre right about the preload bolt. 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.

At some point the crank has become loose and the splines on the crank and the spindle may have worn away at each other. If your cranks are square taper once youve had them come loose youll have dammaged the taper and they will keep coming loose.

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