I'm mounting a Hollowtech crank on a late model Hard Rock. It hit me last night that I don't know the torque spec. for mounting the cranks to the BB. Does anyone know the spec? It's an older Octalink with inboard bearings. Thanks

The recommended bottom bracket cup torque is 50-70 Nm (435-608 inch-pounds)

The recommended crank fastening bolt torque is 35-50 Nm (305-435 in-pounds)

If the crankset is brand new and has not been mounted before there will be a full turn or more of the bolt where it is feeling quite tight but has not yet met the torque spec and is forming the aluminum crank to the axle. It is very important to keep tightening to the specified torque. IMO most of the failures that gave this system a bad rep are due to installers not using a torque wrench and stopping with the bolts felt tight.

The same failure causes most of the reported problems with square taper bottom brackets and cranks too.

Thanks, I've got the correct torque wrench and will make sure it is at least the min. spec. Thanks Again.

Also be sure the splines are fully engaged before torquing. Search for a couple of informative threads on techniques for installing Octalink BBs. (Unless like me you find them dead simple.)

+1. It is possible to install the crank with it's splines opposing the bb splines instead of interlaced with them and that will ruin the interface as soon as the bike is ridden.

If you are installing an Ultegra or Dura Ace crank with the autoextractor feature, unthread and remove the outer ring before installing the crank. That lets you see inside and assure the splines are engaged properly before you install and tighten the crank bolt. A 105 crank does not have the autoextractor collar so you can see whats going on without removing anything else.

Another thing the OP will want to do is at the very least grease the splined interface or anti-seize it if the bike gets ridden outside. Seized octalink cranks are NOT fun to remove.

They made octalink bb's with external bearings?

Since this is a mountain bike, is the bottom bracket/crank v2 octalink? With these,the splines are deeper than on Octalink v1, and you can align the splines and then push them manually together a bit to make sure the crankarm is going onto the spindle properly before you use the bolt to tighten things up. In other words, you can engage the splined interface simply by pushing, by hand, the crankarm onto the spindle with Octalink v2. V2 covers all the Octalink mtb cranksets except XTR I believe.

Re Sheldon:

* The original "V1" type for:
o XTR (BB-M952 9-speed) 112.5 & 116 mm lengths
o Dura-Ace (BB-7700 9speed) 109.5 mm (double) & 118.5 mm (triple) lengths
o Ultegra (BB-6500 9-speed) 109.5 mm (double) & 118.5 mm (triple) lengths
o 105 (BB-5500 9-speed) 109.5 mm (double) & 118.5 mm (triple) lengths

* The later "V2" type for:
o Deore XT (ES70/71)
o Deore LX (ES70/71)
o Deore (ES50/51)

The V2 BBs work with FC M752, FC M751, FC M572, FC M571, FC M510-8 and FC M440-8 cranks.
o Tiagra 2005 (4401,4404)
o Sora 2005 (3301,3304)

also:

V1 7710 DA Track 109.5mm

In the bigger picture, Octalink is one of the easier things to get right without a torque wrench, because the Octalink crank is intended to bottom out onto the inboard end of the spindle's splined section, and when it does, the resistance ramps up so abruptly it's blindingly obvious (famous last words ). So if anything, roccobike, aim for the high end of the torque range just to be sure the crank's fully seated.

Like operator said, grease or anti-sieze the interface. If your cranks don't have auto-extractors, then when you're extracting the arms with a conventional puller, do make sure to remove the washer from under the head of the bolt before you insert the extractor. They're very slim washers so they're easy to overlook.

Me experience is that when new they do not ramp up abruptly to the proper torque. They ramp up abruptly to pretty tight and then they need to be turned quite a bit more before they reach proper installation depth and proper torque spec. I agree with aiming for the high end of the spec. Tightening them until the torque ramps up and then a smidge more by "feel" will likely result in a loosened and ruined crank.

My experience is that there is a small hump (maybe what you're calling "ramp up abruptly to pretty tight") in torque as you mesh the splines (and I always mesh them by feel, but others may be more visually oriented). Then several turns before the splines bottom, then a fast ramp - maybe 1/4 turn? I see no reason to aim for the high end of the spec; the hump isn't anywhere near the spec ... unless you haven't meshed them correctly. But that should be obvious.

Exactly.

Either visually inspect the splines to check for engagement or if you have enough experience to know, how much the crank SHOULD slide onto the spindle that also helps. After doing a couple cranks, you should have enough experience to tell right away, even without being able to see it whether or not the splines are properly engaged by how far the crank slides on and how it behaves when you are tightening the bolt.

What I'm referring to by "ramp up abruptly" is the point at which the bolt no longer wants to turn because the crank is fully seated at the far end of the splines, and there's nowhere further to push the crank to. Not the initial soft swedging where the crank is obviously (to us, anyway) being pressed further and further onto the splines. Shimano also has made certain square-taper cranksets that were designed to bottom the crank arm onto a collar on the spindle, and it's the same story: tighten until full seating occurs, then stop.

I haven't seen that myself... of the customers' bikes I see, many do not have their Octalink cranks fully seated, but I can't recall any in recent memory that self-destructed as a result of being incompletely seated. The main hazard I see with Octalink installation is the problem the guys already described above: getting the splines misaligned during installation and mangling them. For those who can't do it sight-unseen, removing auto-extractor caps and getting a direct visual is the failsafe method.

Overall, I liked my Octalink cranks pretty well. I remember sticking Ultegra 6500's on my old Cannondale full-tourer in place of my venerable-but-cracking XT M730s, and noticing an improvement in stiffness just launching from a stoplight. It wasn't a bad system really, other than the finicky roller-bearing XTR and Dura-Ace variants

Finicky or not, the roller bearing variants of the octalink bb's are superior - if you are prepared to do more maintenance over the non roller version. It's stiffer, lighter and can be made to have a much lower drag by removing seals. I will be replacing my dura ace 7710 with the higher maintenance version for my good weather only bike when it wears out (probably in a really ****ing long time)

It's basically a cup/cone octalink bb, where every part can be replaced/overhauled as needed, for those that want that anyways.

I have only done mine but my understanding is when new the shape of the "bottom" part of the axle spline and that of the cranks is not the same. The crank is intended to form to the axle as part of the initial tightening process thereby creating a zero clearance fit. This only happens on the initial installation and results in a sort of squishy ramping up of the torque over a half a turn or more. When it first bottoms out it feels quite tight but still needs to be tightened quite a bit more to finish the process. Any time after that, when they are removed and reassembled you will get that bottoming out and then a fast ramp up in torque as you describe. When I put my new one on, it got so tight I could barely turn it with my short ratchet, when I put my torque wrench on it, it went another half to full turn before it reached the spec. Use a torque wrench and you will be fine. I don't recommend putting brand new ones on by feel.

When I say, "by feel" I mean getting the splines to mesh. I always use a torque wrench to set final tightness, though I suspect Octalink is less vulnerable to under-torquing than square taper.