So I'm having a problem with octalink LH crank. One fell off a few months ago, probably '04 model. I tightened it up but it happened again. Having had similar problems with square taper, I replaced the crank, admittedly with a second-hand one off the forums.

Worked fine for a month or so until that one came undone too. Oh dear I thought, tried again with some loctite but no good. Must be the BB. So I checked the splines on the BB and there was the minutest wear on one of the splines, couldn't see that anything else could have been causing it. Annoying as the bearings are perfect. One brand new bb later and my crank came loose on the way to work.

Any ideas? do I need to buy a new crank?

Thanks

You need to replace both at the same time and probably the crank bolt too.

Unfortunately when one goes it usually takes the other with it. This happened to me a while ago and replacing all three solved the problem.

IME the correct torque setting for an Octalink crank bolt is as hard as you can physically tighten it.

I've been running octalink for ages, i think once you've fitted a crank you need to check the tightness for a couple of rides after. Once you've done that they generally stay tight. If they start getting even the tinyiest bit loose it accelerates and before you know it they start falling off.

Other than that I've no idea, both my setups have been rock solid and trouble free.

Grease the splines, loctite the bolt and tighten as much as you can. it shouldn't ever come loose

Happened to me a couple of times with a deore octalink crank set, also tried loctite to no avail. In the end it just seemed like a good excuse to upgrade to a new SLX crank set.

The old cranks are now resting at the bottom of my spares bin to be used in emergencies only.

It may be worth thinking if you are just throwing good money after bad to try and fix a re-occuring problem.

I can't see how the BB has worn, it's much harder material than the cranks

I still run Octalink on all my bikes & TBH I've never had one come loose so can't really help with the cause

me too, i have a 105 octalink on my commuter (dont know what version but the BB looks a bit like an isis and is hollow).

don't have a torque wrench but set it to 'effin tight, any more and it strips the threads' no probs in 3k miles

having said that i think you can overtighten these things cos it puts too much pressure on the soft alu crank arm and widens it a bit…