Shimano Octalink, Ultegra BB and Ultegra Cranks. Removed from my road bike, fitted to a new frame, now they keep working loose and I’m not looking forward to the potential expense!

What have I done wrong and is the situation recoverable? Is the crank bolt working loose and would thread locking that help?

Cheers

Thread lock is well worth a go in my experience.

Time for a new crank arm fixing bolt, if the kit is slightly old or worn, threadlock is only a temporary solution.
Number 1 in the diagram.

He’s got Octalink though, not hollowtech? If you have a spare crank bolt use that, if not I have used the threadlock and it has lasted as long as the bottom bracket. It depends how much play there is in the system.

Cool cheers, not sure what bolts I’ve got lying around, but if I don’t have one I’ll find one on eBay etc and give that a whirl with some threadlock.

The Octalink doesn’t have pinch bolts or end cap then? Live and learn.

Crank arm fixing bolt just pre-tensions the system doesn’t it?

Octalink has more in common with a splined square taper system than hollowtech 2.

Octalink has more in common with a splined square taper system than hollowtech 2

That was my point, thanks for explaing it better 😉

So what’s actually happening for the cranks to come loose? Is the bolt unscrewing itself?

It can be yes, just enough to allow play. Threadlock is a quick way to test the theory.

Cool, will clean the bike up and properly dismantle to see what’s what.

When assembling the crank onto the bb axle use only a very small amount ( thin flim) of grease. If you use too much it will pack down in use & come loose.
Cheers
Jeef

He’s got Octalink though, not hollowtech?

Hollowtech 2 is the external bearing system, Octalink was Hollowtech ‘1’.

The hollowtech refers to the fact that the crank arms are hollow, not the actual BB system. I.E. Deore Octalink was never Hollowtech, and I don’t think the Deore external bearing cranks are either.

OP – check the threads in the BB. There may be some swarf in there meaning the threads are slightly stripped, meaning you need a new BB. If not, try a new crank bolt, they cost £2.99 or less from your LBS.

Right, checked the crank bolt threads and the threads on the BB, these are fine. However the engagement points on the crank arms are gouged to bits over about the first 3mm of their length. I’ve reassembled with less grease and a lot of threadlock on the bolt. Will take it for a spin at some point, but I strongly suspect they are dead metal now!

Anyone got a spare drive side crank arm, compact triple and octalink?