Recently acquired a btwin rock rider 540 from a friend, i’m not sure how old it is but all i know is that there was problems with the pedal, i realised that the pedal was completely destroyed(first pic), and so i brought a new one. Now the new pedal has been damaged after 30~ minutes of riding(second pic, damage is small but the pedal doesn’t feel right going over the top), anyone know a fix?
by LegalKichtenPea
9 Comments
Could you take a picture of the bottom bracket too? (the thing it attaches to)
It looks like you’re not tightening it enough. Though having that much damage after only 30 minutes is a bit odd if so.
For a standard crank you need to use a torque wrench and install it to roughly 35-40nm. Then test ride the bike for 5-10min and then retorque it again, because riding can cause it to loosen slightly.
If you are certain it is being torqued to spec and continuing to fail, replace the bottom bracket.
The damage you have looks like an under torqued crank arm.
There’s 2 slightly different square BB standards, JIS and ISO. Should’ve been able to tighten it up to work though, sometimes you really have to put more muscle into it when tightening it
Get something [like this ](https://www.amazon.com/BOLANY-Mountain-Crankset-Integrated-Compatible/dp/B0CFDNRPRZ/) type of crank set and BB and it should work a lot better and not give you issues.
Crank bolts need to be quite tight. As suggested, probably under-tightened.
Your crankarm did not sit tight enough on your bottom bracket spindle.
There could be three reasons.
1. The square end of the spindle was misaligned against the square hole of the crank arm (I don’t think that this is the cause)
2. The square tapered end of the spindle protruded through the square hole to the other side of the crank arm. Thus it could not be tightened by a screw. (possible but cannot remember ever seeing that with a new crank arm).
3. The fastening bolt had not been tightened enough and quickly became loose.
As a rule of thumb: get a key that has a lever about the same size as the crank arm, a ratchet with a bit or nut works also.
And then tighten the screw using the crank arm and your key for leverage until it becomes really tough to screw the bolt any further. That is a lot of force.
What kind of tool are you using to torque the arm down with?
A square taper crank arm typically gets installed to ~40 Nm which is a hefty amount of torque. You **will not** be able to achieve this with a crappy multitool. You’d need a decent sized L-shaped allen key and good technique, or even better, a ratchet + corresponding hex bit.
With that said, you’ll obviously need to replace the existing crank arms with ones that aren’t gouged out now too.
In addition to other advice, do not apply grease to the crank arm or the bottom bracket.
Your bottom bracket is steel and the crank is aluminum. Greasing will allow for the crank arm to push too far onto the bottom bracket which will expand it and cause similar issues.
Have you tried…. but out fewer watts?
Torque your bolts to spec and put blue thread locker.