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.

A loose crank is usually a result of loose bolts or damaged threads, or a damaged bearing. But, how do we fix all this problem?

Keep reading the post to know how to prevent loose crank on a bike with proper maintenance.

Primary Reasons bike left crank arm keeps coming loose

bike let crank arm loosing fix

1. Loose Bolts / Damaged Threads:

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

Let me explain.

The bolts are made of rigid steel, whereas the crank is made of soft aluminum. Sometimes, the bolt gets loose and rubs with the threading.

As aluminum is more flexible than steel, the thread gets damaged. Thus, the bolt gets loose and 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 the crank arms

Crankarm repair, as well as maintenance, is crucial for eliminating losing issues. You can either DIY as mentioned below or rely on professionals to do it.

You can definitely save good money by doing it yourself. Moreover, it’s fun to take care of your beloved bike yourself.

Tip-1: Set it right

bike crank arm fixing

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

Make sure you set the left crankarm 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.

This way the bolt won’t get rusty and will stay tight in the future.

Moreover, friction between bolts and threads decreases by thisby doing this. And the chances of threads being damaged decreases.

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?

There is no good answer to this question. Why should you maintain a routine for it? Just check your bike before every ride, tighten the bolt if it is loose and then start your ride.

The crank wrench I suggested above is compatible with nut-style and screw-style bolts. Or a set of Hex keys can also help.

Just remember not to overtighten the bolt.

Tip-3: Replace the bottom bracket

If the bottom bracket is severely wired out on threads or spindles, then your only option is to replace it.

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 , 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 in total.

How long does a bottom bracket last?

It depends on your type of ride. Again if you ask, a high-end bottom bracket lasts for as long as 10,000 miles.

On the other hand, a mid-range bottom bracket might last half that.

When should I replace my bike crankarm?

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

Or, it would be best if you replaced it when the mating hole is worn, and it is not a good fit.


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

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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