The pedal, crank arm, and drivetrain are the most important parts of a bike. But it’s the crank arms that go through the pressure every day as you pedal away on your bike. So, it’s not a surprise when the bicycle crank arm keeps coming loose.
It happens to every bike, no matter how premium it is. The only difference is that high-end bikes experience it far later in its life.
What causes the arm to become loose? There are a few reasons. It might be a loose bolt, worn-out bolt, broken threads, or damaged bearing. Some problems don’t take even a minute to fix, while in other issues, you have to replace an entire bike component.
In this article, we’ll go over the typical causes behind a loose crank arm and the possible solutions to your problems.
Factors That Cause The Bicycle Crank Arm Keep Coming Loose
Let’s have a look at the root of the problems you’re facing.
- Loose Bolts
This is a common issue but an easy fix. As you use your bike daily, the bolts on your crank arm get loose due to vibration. You just have to tighten it to fix it.
However, if the issue persists and shows up instantly after you fix it, the cause might be one of the following.
- Broken Threads
The bike’s crank arm is usually made of aluminum, at least when it comes to budget and mid-tier bikes. On the other hand, the bolts are steel.
We know aluminum is quite flexible compared to steel. Over time as you tighten the screw, the threading of the crank arm gets cut.
When the threading becomes damaged, the crank arms become loose. It can’t be fixed by simply tightening the bolt.
- Worn Out Spindle
Sometimes the bike can have a spindle mechanism in the bottom bracket. There’s always a chance that the spindle gets worn out. If this happens, then crank arms on both sides become.
- Damaged Bearing
The bearing system in the bottom bracket can also be a culprit causing the issue. When the bearing gets damaged, the whole bottom bracket needs fixing.
How to Prevent Bike Crank Arm from Becoming Loose
You could prevent a world of trouble by just using a sufficient amount of grease on your crank arm during installation. And every once in a while.
A little bit of grease on the bolts and threading will go a long way to protect your bike’s crank arm.
And it’s good practice to check your bike’s condition before you go out every day. Maybe it’s the loose bolt arm, or the pedal needs to be smoothened out a little.
However, there could be a simple fix that you overlooked that resulted in a broken piece of equipment.
How to Fix A Loose Crank Arm
Fixing the crank arm is a straightforward process. Here’s how you can do it yourself.
Step 1: Removal
Use the appropriate wrench to remove the crank arm.
Step 2: Inspection
Check and see which part is causing the issue.
Step 3: Replace Or Repair
If it’s just a loose bolt, you can simply tighten it. However, in most cases, it’s the threading in the crank arm that gets damaged.
You could try to make a thread again. But it won’t last long. It’s better to buy a new set of crank arms and replace the existing ones.
If the bottom bracket has worn-out threading or spindle, you must replace it. It’s not worth the time and effort to fix.
How Much Does It Cost to Replace A Bottom Bracket on A Bike?
I’m a DIY enthusiast. So, my first option is always to buy the parts and replace them in my home. A BB tool is required to do the job. This tool and a bottom bracket won’t cost you more than a hundred bucks.
On the other hand, if you take it to a bike repair shop, they’ll charge you 100-150 bucks. The labor cost takes a chunk out of it.
If time isn’t an issue for you, take the DIY solution.
How Long Does A Bottom Bracket Usually Last?
There’s no fixed period. It depends on how frequently you ride your bike, and of course, the quality of your bottom bracket components matters greatly.
For a high-end bike, the bottom bracket may last 10 thousand miles. For mid-tier bikes, the longevity is half of that.
There’s nothing to be worried about if your bicycle crank arm keeps coming loose. It’s the part that moves the most and takes all the pressure from your pedaling. However, if it occurs, you need to take care of it quickly. Otherwise, you may need to replace the whole crank arm component.