531Aussie

Yep, my left Dura-Ace crank come off while I was riding. I was lucky not to crash. I was riding off the saddle, but just happened to have my weight on my right leg at the time.

It may've had a little play in it before it came off, which I assume could've done some damage. I thought the movement was a worn cleat. I put it back on, tightened it way up, and rode home slowly. Yes, the tension nut/cap/bolt thing had came off.

So, are the alu splines on the crank likely to be too damaged to work properly?

I had a look at the splines, but can't tell if there's been any 'flattening'. When I put the crank back on the axle, before doing the bolts up, it's not as snug as the others i own.
I tightened it way up again, and it feels ok by hand, but I haven't ridden it since.

Is it just a case of try it and see?

I can't believe this happened to me, because I tend to tighten stuff pretty well, and it's never happened before.

Thanks

FastJake

Try it and see, you have nothing to lose now. If you ruined it there is no way to repair it so you might as well try.

This will be an expensive replacement, probably a good time to invest in a torque wrench..

Andrew R Stewart 

The take away i had was the need to periodicly do some preventitive maintance. So many people only do corrective bike work after there was a problem. So many times the problem could have been avoided with a little bit of effort a few weeks prior.

To the question of whether the arm is toast- As mentioned try it, but maybe in a trainer stand for a while... And don't forget to monitor the pinch bolts' and arm's retention on the axle. Andy.

531Aussie

Thanks for the replies. I usually do check the bolts after about the first 10 to 20km, but I got slack with these ones.

There's a slight chance I didn't do the bolts up properly, which is odd for me, because I have 9 sets of these cranks (I have crank length issues ), and I'm always taking them on and off my bikes.
Ah well, 'luckily', this is my oldest set of 7800s (they still have embossed markings), so I'm not totally devastated.

FBinNY 

+1 mount it, tighten it properly, make an offering to the god of bike repair and see if you're lucky today. There's a decent chance it'll be OK, otherwise you'll replace it. There's no percentage in tossing it before trying.

davidad

Nothing like a torque wrench to make sure th bolts are going to stay on.

Lexi01

I never trust those dodgy, lower-end components.

Andrew R Stewart 

Most current components that recocomend the use of a torque wrench is not for the bolts (coming loose) but for the component that the bolts are keeping tight. Components are getting so light weight that more and more of the fudge factor in strength is being lost. Carbon is a poor material if stressed in compression. The very small amount of thread overlap that the smaller bolts have will strip out at the torque levels of yesteryear. So the practices of how a mechanic would tighten bolts in the past are now found to be too tight for the components. The manufactures have to limit the torque levels to prevent the component from failing (like a seat post becoming compressed or a stem binder bolt stripping out). This is why one needs to use carbon assembly paste where grease use to be used.

There was an interesting mention in a bike mag a few years back. A USA manufacturer sent their tech guy over to the TdF to check up on the pro mechanics' practices and how the parts held up to pro racing. In the beginning of the race the parts were, for the most part, well assembled. Properly tightened, assembly paste as needed, reinforced as needed (think carbon steerers). But by the end of the 3 weeks many parts were found to be over tightened and some showed the effects of this abuse. The tech guy found that after each day's stage the mechanic would "place his hands" on the bike and check all fittings. Bit by bit this little retorquing/tightening resulted in the hardware being too tight. So even pro mechanics sometimes don't understand the need for proper tools and procedures. Andy.

Andrew R Stewart 

I should have also mentioned that many of the current (and smaller then in the past) hardware uses a dab of thread locker to further help the bolts from coming loose (at the low torques demanded today). Andy.

Kimmo 

Don't trust it.

Besides, I could use something nicer than the crappy Sora cranks I have on my modern bike...