-1

This is a very small fix for a very few bikes on the road...

I was looking online for a solution to the very slight skipping when pedalling my S S Marin Muirwoods 1996 Road conversion.

Obviously, it's an older bottom bracket in my case a British standard, Octalink 73mm (I think). Anyhow chain was new so I knew it wasn't a stretched chain. So when I went online it said in a number of articles, it was the BB wearing out. Okay so take the crank, chain etc off and out and see definitively the BB size to order a new one.

I went to remove the hex bolts holding the crank on, and Oh hello, the hex bolts were both finger tight.

There, solution tightened up the two hex bolts and voila! ... fixed.

6
  • 5
    Welcome to Bicycles.SE! If you want to share knowledge, the way to do that is to write a question, and post an answer to your own question. Jan 29, 2022 at 7:37
  • 3
    I disagree, it's refreshingly honest to have just this post even if it's not according to the site format instead of coming up with an obviously fake question and then self-answering it.
    – ojs
    Jan 29, 2022 at 14:36
  • 2
    To confirm the community rules, post a question first and then an answer. You still may get better answer to your original question.
    – nightrider
    Jan 29, 2022 at 14:37
  • 4
    @ojs It doesn't have to be that way though. The OP could append to the end of the post: "Why did these bolts come loose?". Conveniently, we already have a rant from the J-man to cover that.
    – Paul H
    Jan 29, 2022 at 14:38
  • 1
    @PaulH good point
    – ojs
    Jan 29, 2022 at 15:50

1 Answer 1

-3

(too long for a comment, posting as an answer)

Why the bolts loosened is due to a flaw in Octalink. It lacks press fit unlike any decent crank-to-bottom-bracket attachment method such as square taper or ISIS. Because it lacks press fit, the cranks can rotate back and forth on the bottom bracket spindle, loosening the bolts gradually.

For users who always stand on rough ground left foot forwards / right foot backwards, never the other way, the spindle only sees torque in one direction (forwards torque from both standing on rough ground and pedaling). Thus, the crank bolts won't self-loosen.

For users who always stand on rough ground right foot forwards / left foot backwards, never the other way, the spindle sees reverse torque from standing on rough ground and forwards torque from pedaling. The alternating torque due to the flaw in Octalink causes the bolts to self-loosen. Probably the left bolt is the most affected, but with time both of the bolts could self-loosen.

For users who alternately stand on rough ground both ways, the spindle sees alternating torque from standing on rough ground alone (plus forwards torque from pedaling). This will very rapidly loosen the crank bolts.

So unless you change your riding habits to eliminate the reverse torque on the spindle when standing on the pedals on rough ground, the bolts will continue self-loosening. You will need to continue tightening them -- often!

Any other bottom bracket type such as square taper, ISIS or Hollowtech II would not suffer from the same crank bolt self-loosening flaw.

1
  • I think by this point you've accused pretty much every component in a bicycle of being full of design flaws Jan 31, 2022 at 0:22

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.