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Crank Arm Keeps Coming Loose – 5 Causes & Solutions

Written by Gary Johnson / Fact checked by Henry Speciale

crank arm keeps coming loose

One of the most annoying moments has to be when your crank arm keeps coming loose. The hassle of trying to figure out what went wrong & how to fix it can become a real bother—that’s for sure.

Usually, the number one reason why your crank arm keeps coming loose is that the bolts or threads are damaged and worn out.

If this often happens to you, we know the struggle! But it’s not the only cause of a bike crank loose. There are many more reasons why, some of which may be applicable to you.

Reasons the Bike Crank Arm is Loose

1. The bolts are loose and damaged.


When the bolts or threads of your bike are damaged, this results in loose bike crank arms.

Since the bolts are often manufactured in the material of hard steel, while cranks, on the other hand, are soft aluminum, the thread gets worn out & the bolts turn looser when already unsecured bolts rub against steel cranks.

To fix wobbly crank arm caused by this reason, you may purchase new bolts, replace your existing ones, and grab your preferred tool to tighten bike crank.

Use a screwdriver to loosen the lock nut screw, then tighten up the nut with a wrench before securing the nut screw. While you tighten bicycle crank, replace the stripped or worn threads to prevent the same problem from re-ocurring.

2. Incorrect Installation


Another common reason why your crank arm is loose is because it may be installed the wrong way.

If you have just replaced your bike cranks and your bike pedal keeps coming loose, check if they have been tightened correctly or whether there are missing components like threadlockers.

The same recommendation applies if your crank arm fell off while riding or you notice that your bike’s crank arms not aligned.

It is wise to check the pinch bolts and see if the correct torque has been applied in these cases. If not, use a torque wrench to readjust.

3. The bearing is damaged.


If the bearing of the bottom bracket is worn, this also causes the bike crank nut to be loose and the bicycle pedal arm to be wobbly.

To fix this, all you need to do is first dismantle the bearing, replace it with a new one, grease the new component, and tighten the bicycle crank back.

4. The spindle is wired out.


A loose bike left crank arm is a common sign that the spindle may be wired out. Some of the reasons why your spindle may be problematic are improper installation, poor lubrication, or incorrect alignment.

In this case, oil the crank bolt and ensure the pinch clamp is 180 degrees from the spindle hole.

5. An unfitting bottom bracket


If the bottom bracket and the crank arms aren’t compatible with one another, the attachments can loosen, which can affect the entire crank.

Shake the crank and see if the bottom bracket moves while the frame remains steady. If so, you need to examine the bottom bracket and see if it’s loose or needs replacement.

Frequently Asked Questions


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

A bottom bracket replacement price may vary from $30 to $50 if we count labor costs only. If you buy the bottom bracket as well, the expense can reach $100 or more.

How long does a bottom bracket last?

A bottom bracket generally lasts for about 1-2 years, but if it’s always exposed to moisture, its longevity may be compromised, and you may need to replace it more frequently.

When should I replace my bike crank arm?

Replace your bike’s crank arm if you notice cracks on it. Another sign to look out for is if the threads of the pedal arm bike becomes stripped or if the hole made for the bottom bracket wears or there’s creaking when you rotate the crankset.

Why did my BMX crank bolt keep coming loose?

If your mountain bike pedal arm and its crank bolt keep coming loose, specifically if your bike is a BMX bike, this is often a sign that the threading of the bolt is stripped.

Why did my Hollowtech crank keep coming loose?

If you have a Hollowtech crank, the reason why it keeps coming loose may either be wrongly spaced bottom brackets or wrongly placed cranks, which lead to pedal axle loose instead of secure.


Whether it’s the annoying creaking sound, a wobbly pedal, or the most common instance–your bike chain line keeps coming loose on pole, they all just mean one thing: your bike crank arm keeps coming loose!

But with this article, you won’t have to wonder why. And when you know the why, the what & how follows. You can fix the problem in the right way and get back to cycling!

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