My son has a 29" BMX with a 3 piece crank set with an 8 spline spindle, with pinch bolts and spline bolts in the end. This is the second time that the crank arm on the non drive side has "broken off" while he was riding. Both times the spline bolt was in place and broke. You can see the broken piece of the bolt still in the spindle in the picture.
The first time this happened I didn't think much of it and just replaced the bolt. But it happened again within 2 months of replacing it. I'm not sure why this is happening, because it doesn't seem to me like that bolt should see much stress while in operation. Most of the forces are on the spindle and bearings, right? That bolt is just preventing the crank from sliding off the spindle? Maybe I'm over tightening?
If anyone has experienced this and can give me ideas how to prevent it, I'd appreciate it.
by rscam09
1 Comment
if you use grease to lube the bolt, try less torque, and remember, torque the spline bolts first, then the pinch bolts.