Why Does My Left Crank Arm Keep Coming Loose

You can tighten that bolt and everything feels fine until you start riding and putting pressure on the arm and it wiggles its way lose again. A stripped crank thread and a rounded out arm hole.

Crank Loose Falls Off Bike Boo Boos

You need a new crank.

Why does my left crank arm keep coming loose. If the arm is damaged no matter how tight the bolt is torqued it will not stay tight on the spindle. Re-torqueing the bolt will keep the arm on for a short amount of time but eventually will critically damage the crank arm bolt. Once a crank bolt comes loose and the crank arm is damaged from riding with the bolt loose loctite will not help out.

You can try locktite but Ive had no success with that either. The only fix to that is a new crank arm. The steel axle will usually survive.

Step 2 Position a cotter pin press over the crank with the bolt attached to the press against the threaded end of the cotter bolt. A retaining compound eg. At some point the crank has become loose and the splines on the crank and the spindle may have worn away at each other.

It doesnt have to do with quality. Best bet is to have the left hand arm replaced. But I have seen many that havent had a torque wrench used and they usually come in for either a crank arm replacement or a crank set install.

You will have no choice but to replace it. Somehow this damage causes the crank arm to wiggle enough to unscrew the nut little by little until it just falls off again. Its not sure your cranks are dead yet but if you continue to ride them with the same bb you will most probably end up ruining them both try and find out whats the culprit the bb or the cranks or maybe theyre not working together.

In this situation you dont want this to happen so remove the metal piece first. Thats because the spindle the axle the crankarms spin on is made of steel and the arms are aluminum. The splines on the crank arm can be ovalized or otherwise damaged if ridden when loose.

The BB axle is hardened steel the crank arm is generally aluminum. The metal piece will probably. Aluminum is softer than steel so if the interface is loose at all you start rounding out the opening for the spindle.

When the crank arm is loose and you pedal with it you damage the four corners of its socket that rest in the axle. Luckily the industry has realized this and its often possible to buy separate left crank arms to replace the damaged ones. But remember each time they loosen is.

One can of course try to tighten the arm but very often the damage means that the arm will continue to come loose. -if your crank is developing the profile wobble check and see if when the bolts are tight if the crank arm can be moved up down on the spindle slightly not side to side this indicates that your splines are wearing out is why it keeps coming loose-if your threads in the spindle and the bolt are still good and not stripped. Possibly the first time it came loose you damaged the crank arm so that no matter how tight you lash up the bolts there will always be a tendency for it to work looseIf thats the case you need a.

As someone pointed out above with a newly fitted crank it will bed in and needs regular tightening for a few days. If youve been repeatedly riding with a loose crank arm it could be that its now damaged. If your cranks are square taper once youve had them come loose youll have dammaged the taper and they will keep coming loose.

You could try tightening with lots of torque grease on the square taper and threadlocker eg. I say may because there is a short section that is not splined see. When the crank loosens the arm rocks back and forth slightly rounding out that square.

Only thing that would keep a damaged crank arm on is JB Weld. It is more likely the left crank arm became loose developed wear and now needs to be replaced. Remove the nuts from the cotter bolts that thread through the crank with an adjustable wrench.

A neighbor kids bmx left crankarm kept coming loose so I pulled the crankarm off cleaned it good didnt really notice any excessive wear or. The left crank arm keeps coming off the bolt keeps coming loose. If you found a piece of metal over the crank arm bolt which let you see the bolt but not remove it this is a self extracting bolt assembly.

This means the BB spindle is square and the hole in the arm is also square. LOCTITE 648 on the square taper is even better than grease. All cranks will do this.

I did it up to the correct torque settings not the easiest thing to do on a rotating shaft and its been ok so far. Blue Loctite but in a pinch any kind of glue works on the threads. A worn cotter can cause a loose crank.

I thought Id bent the pedal axle at first. Its a really odd feeling. I have replaced it with a new one which had some grip on it but it came off this morning and had worn down quite a lot.

The bolt pushes against the metal piece as it unscrews forcing the crank arm to come off the bottom bracket axle at the same time. My left crank arm bolt came undone the other day after 400-odd miles.

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