Why Does My Bike Left Crank Arm Keeps Coming Loose?

The crank arms and pedals go through the most pressure while riding the bike. That’s why the loose crank arm is a common problem every cyclist faces.

However, it can happen because of loose bolts or broken threads, or even damaged bearing. But, how to fix all these problems?

Don’t worry, mate. Your freaky friend is here. I am gonna break down the problem and suggest the best probable solution for all crank arm-related problems.

Now, it’s all up to you. Keep reading the post to know how you can prevent loose crank arms without frequent fixing.

Major Reasons bike left crank arm keeps coming loose

bike let crank arm loosing fix

Before going for a solution, you have to know the root of the problem.

However, a loose crank arm can appear because of one or more than one reason. What are these reasons? Let’s dig them out.

1. Loose Bolts / Broken Threads:

Mostly appear in the square taper bottom bracket; a loose bolt and broken treads are related to each other. Asking how?

Let me explain.

The bolts are made of rigid steel, where the crank is made of soft aluminum. Sometimes, the bolt gets lose and rubs with the threads.

As aluminum is more flexible than steel, the thread gets damaged. Thus, the bolt gets loose, and this keeps going in a loop.

2. Wired Out Spindle:

If your bike features a spindle bottom bracket, there is a chance that the spindle gets wired out, and the arm gets loose.

3. Bearing Damage:

Sometimes, the bottom bracket itself causes a loose crankarm. When the bearing system is damaged inside, the arm skips while paddling.

Thus, an artificial loose crankarm appears.

A quick fix to the loose crank arm

It’s better to prevent the loose crankarm than fix it after a break.

For that, use Grease while installing a new crankarm. Also, check and repair your bike before every ride. 

There are various types of crankarm mounting systems. You will need a Crank Wrench or Hex Key as per the system.

Check your bike before going out for a ride. If the arm bolt is too loose, then tighten it and go.

How to maintain or repair left crankarm

Crankarm repair, as well as maintenance, is crucial for eliminating losing issues. However, you can rely on professionals for it.

But, you can save some money by doing it yourself. Moreover, it’s fun to take care of your beloved bike yourself.

Anyways I have some pro tips on crankarm maintenance and repair. Follow them if you don’t like frequent breaks and fixes loop.

Tip-1: Set it correct

bike crank arm fixing

You can avoid loose crankarm by taking some preventive measures. For that, you have to be careful while installing a new crankarm.

Make sure you set the left crankarm exactly 180 degrees with the right one. Then thread the bolt correctly. 

Oh, wait! Don’t forget to apply grease to the bolt before setting it.

Thus, the bolt won’t get rusty, and it will stay tight in the future.

Moreover, friction between bolt and threads decreases by this. So, the chances of threads breaking decrease.

Warning: You may find recommendations for using thread-locker adhesive instead of grease. But I suggest not using these things. It will create more problems when you need to swap the crankarm. Moreover, it has a corrosive nature which is not suitable for metal.

Tip-2: Check, fix and ride

How often should I tighten the crankarm?

I have no answer for it. Why should you maintain a routine for it? Just check your bike before every ride, tighten the bolt if it is loose and then go out.

However, the Crank Wrench I have suggested above is compatible with both nut style and screw style bolts. It should fit your bike arm bolt.

Otherwise, get a set of Hex Key and check which size fits the bolt.

Anyways, after you get the suitable tool, tighten the arm bolt but don’t overtighten it.


Tip-3: Replace the bottom bracket

If the bottom bracket is severely wired out on threads or spindles, there is no alternative to replacement.

Bottom Brackets come in various types and sizes. Take time and do your research to get a suitable one for your bike.

However, you will need a Bottom Bracket Tool to unmount the old bottom bracket.

Before that, uninstall the crankarm with a crank wrench.

Sometimes, you may notice that the thread or spindle is in good condition. But there is still a loose crankarm.

It can happen because of damage bearing inside the bottom bracket.

In that case, you don’t need to replace the whole bottom bracket. Replace the Bearing System instead.

Frequently Asked Questions

How much does it cost to replace a bottom bracket on a bike?

If you do it in a bike shop, it will cost nearly 100 to 150 USD, including the service charge of the mechanic.

Other hands, DIY needs a new bottom bracket and bb tool, which will cost around 70 to 100 USD in total. So, it’s better if you can DIY the repair work.

How long does a bottom bracket last?

It totally depends on your type of ride. Again if you ask, a high-end bottom bracket lasts after rides of 10 thousand miles.

Other hands, you can ride around 5 thousand miles with a mid-range bottom bracket.

When should I replace my bike crankarm?

When the threads for the pedal or bottom bracket are severely damaged, you should replace the crankarm.

Or, you should replace it when the mating hole is worn, and it is not a good fit.


Since the crankarm is the most movable part of the bike, it needs to sit right and stay tight. You can’t go far with a loose crankarm.

That’s why you should check and fix it regularly. Also, take some preventive steps to avoid frequent loose.

However, the prevention and fixing process has been described above.

I have also suggested some tools and accessories that make the process much easier.

Now, what you have to do is to follow my steps one by one.

I hope you will get rid of the loose crankarm and enjoy a smooth ride.


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