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Octalink Crank Fitment Question

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Octalink Crank Fitment Question

Old 06-17-18, 10:01 AM
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Octalink Crank Fitment Question

Iíve been reinstalling and exchanging Octalink BBs searching for the sourch of a mystery click and noticed that my driveside crank bolt doesnít gradually cinch down when I install it on my 7700 BB. It almost suddenly comes to a stop. But when I install on the 105 BB, everything tightens in a normal manner. The left side crank goes on normal on both BBs.
Is this a thing that happens? The spindle shouldnít deform against the aluminum. It looks fine and I have been using octalink V1 road cranks for 15 years but never experienced this sensation of bottoming out.
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Old 06-17-18, 10:32 AM
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It sounds like the taper of the splines has relaxed.
I believe Octalink is tapered in some way along each spline, and that one is supposed to bottom the bolt as the spline tapers tighten up, so the sensation of bottoming seems "soft".

I would consider grinding a very small amount of metal off of the end of the hollow spindle to see if this restores the taper tightness during tightening. But I am not certain if the end of the spindle perhaps serves to assist with preserving the planar orientation of the right crankarm's bolt circle, in which case the grinding would need to be done with lathe-turned precision (as with the spindle rotating at considerable speed during grinding).
I think I could make that happen even with the bottom bracket installed, using a high-speed drill attached to the other end while a grinder was applied to the right end of the fast-turning spindle. Really not difficult with the necessary tools at hand.

In a worst-case scenario, I have known people to use Loctite Red on cleaned Octalink splines, but which may require the application of torch heat to later remove the arm.

Last edited by dddd; 06-17-18 at 10:35 AM.
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Old 06-17-18, 11:09 AM
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I've always had to play with them to get them "seated" before tightening up.
Be sure to check inside the crank arm for pieces, or a cracked spline that folds or something when being installed.
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Old 06-17-18, 12:05 PM
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Make sure you have the Octalink aligned right before cranking down. I'm a bit new to Octalink, but it seems like one can put both crank arms on at once, then as one is tightening down, twist slightly to feel for the slot.

The service feature of the original Dura Ace bottom brackets seems nice, but if it isn't working for you, then I'd just replace it.
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Old 06-17-18, 01:00 PM
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Iíve replaced/installed several of these BB and CS and have never experienced this. Iím going to put the 7700 BB back on later since it is all cleaned up and the mystery click turned out to be a grease deficiency on the right pedal spindle threads.
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Old 06-17-18, 01:13 PM
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At this point I thought to ask, which of the two bottom brackets has the crankset in question spent it's working life mounted on?

If one bb is effectively bigger or tighter-fitting in some way, might it have subtly enlarged the opening of the crankarm over time to where it now fits with little to no interference on the bb that it appears to be bottoming on too easily?
This sounds odd given Shimano's excellent reputation for quality control, but small-scale running changes to these bb's might have been implemented to solve some problem with a loose fit, with the expectation that the newer parts would sometimes be fitted to older cranksets but not the other way around. There are date codes on these bb's that can tell you if the looser fit (hard bottoming of the bolt) is occurring with the newer or older bottom bracket.
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Old 06-17-18, 02:53 PM
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Brilliant dddd.
The BB that my CS is snug/normal fitting on is likely newer manufacture sealed cartridge 105. And the 7700 BB is most likely earlier manufacte date.
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