octalink sucks
 

maybe? just mine?

I finally got my ultegra octalink cranks fixed up to my Dura-Ace BB, and well, it works pretty well- unless i'm going slow. in which case, my left crank arm moves independantly of the BB (and other crank arm, and chain). It's pretty annoying. Am i doing something wrong? Is this a common issue? I'm clearly an idiot for buying the hi-end, yet strangly cheep everywhere cranks. Guh.

Did you cross-match Octalink V1 and V2 crank & BB by any chance?

Did you neglect to seat the crank arm properly in the spindle splines before tightening the fixing bolt?

Installed properly (and of course using the correct model Octalink pattern) they are very durable and reliable bottom brackets and cranks.

www.sheldonbrown.com and go to V1 & V2 in the glossary for
pix and explanations of difference (mainly V2 splines are deeper).
I had that happen first assembly of my thne new crankset for 9spd
in '99 and chewed up the first few mm of spline on the crank.
Carefully reassembled and made sure everything was fully seated
and torqued the fixing bolts and no further problem with crank
despite the chewed up section. Check your crank for damage
as the BB steel will chewup the softer Al splines easily. Properly
assembled the setup is extremely tight with no slop at all.

Ultegra Cranks and DA BB only came in V1.

Take off your cranks and put them back in. One of the arms is not seated correctly on the splines

Whatever's going on, it doesn't sound good for the longevity of either part. I have to imagine you'll be buying new ones.

Don't go slow.

Longevity wasn't affected on my Ultegras, despite the chewed up
section, cranks are still in service with more than 10kmi with no
problems.

Crank arm not seated properly is my first guess. Pull it and check. You may have already ruined the crank.

i kept pulling off the left arm and checking it, and it always looked right. But when i pulled off the right, it was a big mess.

So, i have it set up more or less right right now. I'm fairly confident that it will run fine for about a month or two, at which point i will have a discount set of power cranks.

note to self: be less stupid.

The one downside to the Ultegra and Dura Ace Octalink cranks with their included autoextractor collars is that you can't see how the arms are seated on the spindle splines when you install them.

I always remove the collars so I see inside and be absolutely sure the cranks are fully seated on the splines before installing the fixing bolts. Once everything is properly clamped down, then I reinstall the collars.

I do it by feel. When you tighten down the bolt you can feel the splines hit and start to engage (or not). I rotate the arm a little to be sure that they're engaging, then note how much I tighten the bolt beyond that point. It should turn a good four easy revolutions past engagement, if memory serves.

If you do it this way, you can't screw up the engagement because if the splines jam you'll get at most half a turn or so before the bolt becomes quite hard to turn.

Otoh, I understand the need for visual confirmation. :p

I guess this is one area where the V2 Octalink design (non-XTR mtb cranks plus Sora, Tiagra) has an advantage over V1: you can push the cranks onto the bb splines by hand a ways before you even need to begin tightening with the bolt. I've never used any of the V1 Octalink stuff, but this isn't possbible with V1, is it?

Yes it is. The splines of the spindle engage the mating grooves in the crank arm a fair amount and, if you look inside, you can see that the splines have mated and the spindle is firmly up against the end of the grooves in the crank arm. That's why I remove the autoex collars so I can see that everything is aligned and seated properly before I screw in the fixing bolt. .

DMF's technique of using the fixing bolt as a "depth gauge" also seems reliable.

Thanks for the info on V1 Octalink, that's interesting. The reason I asked was that I've seen a lot of posts where people have trouble aligning the splines, have special techiques to align the splines, etc., and I've wondered why they don't just look through the holes in the crankarams to make sure everything is aligned and then push the cranks onto the splines by hand to get it started properly. I finally figured that maybe V1 and V2 are different in that regard, but I guess not. I've had two different mountain bikes with XT Octalink cranks, and yeah, I always remove the self extractor rings before re-installing the cranks. On new cranks, the extractors aren't on the cranks yet anyway, I can't imagine why someone would put those on before installing the crankarms. Oh well-