The left crank arm on my bike keeps falling off. The original bolt is gone. I went to a bike shop, and the guy put some random bolt. Fell off after 20 minutes. Went to show him, and he then put a longer bolt for free, which also fell off. Second bike shop I went to said he didn’t have the parts. I’m tired of walking around with a broken bike.
**How do I fix this?**
ernieball2221 on
Use blue loctite
ScootMaBoot on
You will need a new crank arm. Once the crank arm has fallen off, it is usually damaged in a way that cannot be repaired and will keep falling off until it is replaced.
handsomeguy-man on
Most likely the crank arm is worn out by now.
Get a new crank and have it torqued up properly, you may need to retorque after the first few rides even if it still feels right
BD59 on
Replacement.
nommieeee on
New crank arm + new bottom bracket. If bolts keep falling out the threads are toasted as well.
Lucky for you you’ve got a square tapered crank, so any square tapered crank with the same length would work perfectly, plus they are cheap as chips
obaananana on
Wrong screw. The actuall screw presses the crank arn on the bb axle
Affectionate-Sun9373 on
First stop with the grease. Clean the threads out in the spindle as well as you can, use some liquid fire or contact cleaner, clean the bolt. Then put anti seize on the threads. But I the bot keeps falling out, the threads may be beyond repair.
Darknwise on
If the square taper is no longer perfectly square, this will happen over and over. You’ll need to replace the whole bb and possibly crank arm.
Strongly suggest to move to shimano hollow tech if at all possible.
Specific_Mixture5995 on
40ft lbs, red loctite, green retaining compound on taper and 12.9 crank bolts. Retorque after first ride and every ride till it doesnt move
jim2527 on
Once the taper is stretched it’ll always be stretched. You can torque, ride, retorque, ride repeat until it no longer tightened. Sometimes the hole gets so stretched that the BB spindle goes all the trough and. You’re essentially torquing the bolt to spindle versus the crank arms.
It’s very rare that the spindle threads are destroyed but it’s possible.
Obriquet on
New bottom bracket should resolve the issue for you!
People appear to be taking the fact that the crank arm has previously fallen off into account. I don’t think there’s much to this unless the crank arm is visibly damaged.
It’s a tapered bottom bracket and and crank at the end of the day. So if it has deformed in any way it will continue to cause the same issue.
If you’re riding more challenging terrain than the bike may have been originally intended for you might want to consider upgrading the entire crankset to something a bit better that doesn’t use a tapered bottom bracket. These can more evenly distribute for forces exhibited during your rides into the rest of the bike.
Bikedogpablo on
New bike. That’s the rules. N+1
mullaworkshop on
From experience you need a new bottom bracket and crankarm. Just replacing the crank doesnt usually solve the issue.
14 Comments
The left crank arm on my bike keeps falling off. The original bolt is gone. I went to a bike shop, and the guy put some random bolt. Fell off after 20 minutes. Went to show him, and he then put a longer bolt for free, which also fell off. Second bike shop I went to said he didn’t have the parts. I’m tired of walking around with a broken bike.
**How do I fix this?**
Use blue loctite
You will need a new crank arm. Once the crank arm has fallen off, it is usually damaged in a way that cannot be repaired and will keep falling off until it is replaced.
Most likely the crank arm is worn out by now.
Get a new crank and have it torqued up properly, you may need to retorque after the first few rides even if it still feels right
Replacement.
New crank arm + new bottom bracket. If bolts keep falling out the threads are toasted as well.
Lucky for you you’ve got a square tapered crank, so any square tapered crank with the same length would work perfectly, plus they are cheap as chips
Wrong screw. The actuall screw presses the crank arn on the bb axle
First stop with the grease. Clean the threads out in the spindle as well as you can, use some liquid fire or contact cleaner, clean the bolt. Then put anti seize on the threads. But I the bot keeps falling out, the threads may be beyond repair.
If the square taper is no longer perfectly square, this will happen over and over. You’ll need to replace the whole bb and possibly crank arm.
Strongly suggest to move to shimano hollow tech if at all possible.
40ft lbs, red loctite, green retaining compound on taper and 12.9 crank bolts. Retorque after first ride and every ride till it doesnt move
Once the taper is stretched it’ll always be stretched. You can torque, ride, retorque, ride repeat until it no longer tightened. Sometimes the hole gets so stretched that the BB spindle goes all the trough and. You’re essentially torquing the bolt to spindle versus the crank arms.
It’s very rare that the spindle threads are destroyed but it’s possible.
New bottom bracket should resolve the issue for you!
People appear to be taking the fact that the crank arm has previously fallen off into account. I don’t think there’s much to this unless the crank arm is visibly damaged.
It’s a tapered bottom bracket and and crank at the end of the day. So if it has deformed in any way it will continue to cause the same issue.
If you’re riding more challenging terrain than the bike may have been originally intended for you might want to consider upgrading the entire crankset to something a bit better that doesn’t use a tapered bottom bracket. These can more evenly distribute for forces exhibited during your rides into the rest of the bike.
New bike. That’s the rules. N+1
From experience you need a new bottom bracket and crankarm. Just replacing the crank doesnt usually solve the issue.