Damn it! It almost broke my frame. Like you, I also faced this problem yesterday. The crank arm was hitting the frame like crazy. Thus the frame was being damaged heavily.
Moreover, the paddling was getting difficult. So, I have immediately got a fix after identifying the problem. In this process, I understood the situation well and learned how to get a solution to this.
That’s why I am writing this blog today. I am presenting is based on my experience. If you have a different experience, feel free to share it with FreakyCyclist. The comment section is always open for you.
Anyways, you must understand the problem well before getting a solution. So, let’s know why the bike crank arm is hitting the frame.
Why is the bike crank arm hitting frame?
A bike crank arm hits the frame when the crankarm is too loose or bent. Besides, it happens when the bottom bracket is too short or too tight.
However, that’s not all. Let’s dive deep into it.
- Loose/bent crankarm: The crankarm gets connected with the bottom bracket through the nut bolt system. Most of the time, the nuts get loosen over time. But sometimes, the threads get exhausted, and the crankarm keeps losing. Besides, the arm can get bent after a crash. For all these reasons, the crank arm can hit the frame.
- Short bottom bracket: This problem can also arise when the bottom bracket is too short or tight. When the bottom bracket is too short or too tight, the distance between the frame and crank arm gets shortened. Thus the crank can start rubbing or hitting each other.
How to keep bike crank arm from hitting frame
I know this problem needs an instant solution. But you also need to understand how to avoid this problem in the future. Also, try to implement the below tips in your repair work. Thus, you can save the bike from crankarm hitting or frame damage.
- Keep the crankarm tight: If you follow some simple tricks, the crankarm won’t get loosened easily. Thus, you can get rid of this problem. For that, you will need the correct crankarm setting. While setting it, make sure the bolt sits correctly. Besides, you can use Grease or Thread Locker. I prefer grease over thread locker. It’s gentle towards metal and easy to remove when necessary.
- Get suitable BB: As the length of the bottom bracket influences the distance between the crankarm and the frame, it should have the correct size. For that, get a suitable Bottom Bracket. If the bottom bracket is too tight, get a compatible Bottom Bracket Tool and loosen it as necessary.
Advanced troubleshooting: bike crank arm hitting frame
While the bike crank arm is hitting the frame, you must get a fix. If the crankarm is severely damaged inside, it should be replaced. If the bolt is not worn out, you can just tighten it and chill.
However, the procedure is the same for both actions. So you can follow the below steps to fix the crankarm. Before that, get the essential tools and supplies for repair work.
Step-1: Loosen the crankarm
In the very first step, you have to loosen the crank arm. There are different types of crankarms. But primary types can be loosened with either a hex key or crank puller. So, get the correct size hex key or crank puller, and you are ready to go.
Removing the crankarm is easy if the crankset is compatible with hex keys. What you have to do is to loosen the crankarm. But, removing the crankarm with a crank puller is tricky. Let’s make it simple.
First, you have to remove the cap if there is any. Then set the puller in the correct position and tighten it. Now you can unscrew the crankarm easily.
Step-2: Set it up
After loosening the crank arm, clean it if it seems reusable. You can clean it with Chain Cleaner. If the crankarm is severely damaged inside, get a new Crankarm. Consider your groupset model while getting it. Now, set the new or cleaned crankarm to its definite position. Before that, you can apply grease or thread locker on the spindle.
Step-3: Tighten the crankarm
After setting the crankarm correctly, tighten it with the crank puller. When doing it, make sure the crankarms make 180 degrees to each other. Also, make sure you don’t overtighten it. For that, set the crank puller to the crank bolt and rotate it clockwise. Do it until it gets tight enough. Then reinstall the cap.
However, if the crankarm is compatible with the hex keys, you can simply tighten it with a hex wrench.
Frequently Asked Question
How tight should crank arms be?
As I said, you should tighten the crank arm but not overtighten it. SO here comes the question. How tight it should be. Well, there is no fixed rule for this. You may find it written in very few models of crankarms. If you still insist for a number, I can say 40 pascal is an optimal level of tightness for crankarms.
What happens if you over-tighten the crank bolt?
You have learned that a loose crankarm hits the frame. But what will happen if you overtighten the crank bolt? If you overtighten it, the bolt will get stretched. Thus the bolt gets damaged even more and gets loosened more frequently.
Not at all. Overtightening the bottom bracket can cause the crankarm to hit the frame. Besides, it can damage the inner thread of the BB hole. Moreover, the bearing won’t sit right if the BB is too tight. Thus, the paddling also gets inefficient. So, you must not overtighten the bottom bracket.
I hate seeing the shiny blue coating getting exhausted from my bike frame. You can relate to the feeling as it’s happening for the same reasons. I couldn’t let my beloved bike keep damaging. I think you can’t also let it be. That’s why I wrote this blog. I hope it has helped you identify the reasons and get a solution accordingly.
Anyways, the repair work may need some tools and supplies. I suggested the best option for them. You can give them a shot. I hope you get rid of all the problems, save the frame and enjoy efficient paddling.