Dura Ace fc-7710 cranks and octalink unscrewing themselves

Weird one - headed off for lunch and noticed things were all a bit creaky and there was a definite issue with my cranks or BB. They were 100% yesterday.

Stopped and checked and the drive side crank was about to fall off. somehow the self extracting crank bolt had unscrewed and er, self extracted.

Is this even possible or has someone tried to nick my cranks?
tightened everything up but now there is a clunk every revolution. Damaged octalink splines? I hope not...

This doesn't look great, it sounds like the splines in the cranks may be mashed. Is there play in the cranks or just a noise?

well, I've just stripped it all down and cleaning out the splines... they are a potential problem for sure. Little chinks off aluminium taken out of some of the splines and wiping of the grease reveals more metallic flakes. Will thoroughly clean and reinstall but starting to understand the drawbacks of octalink. Damn.

Phew, cleaned everything, regreased and assembled. No Noise! Nothing like a good clean.

the same happened to me on ultegra octalink crankset shortly after the build (brand new parts). it stopped after few weeks and i assume that parts were just binding together

When I first started using octalink ( about 11 years ago ), I was told to install the crank with a decent amount of grease, then ride around for a few minutes before retightening.

I've always done that and haven't yet had one come loose on 5 different chainsets ( both V1 and V2 spline pattern )

Lucky you noticed it in time. I managed to cook a set of 7710 byt ignoring the creak until the crank came off completely.

Yeah, going to be pretty paranoid for a while. I'm already obsessive enough when it comes to little noises and creaks etc. It was strange though, they've been fine for at least 400 miles since installing, and I have checked them. Then overnight - loose!

Certainly don't want to change them, they are excellent cranks.

what i discovered (after first mashing up the splines on a non-driveside), that first getting the self extractor bolts out gets you to actually see the splines engage instead of wild guessing and gentle wiggling.. get the bolt in and tighten, works a treat.