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Installing adjustable bottom bracket - chainline question
I am putting a shimano octalink v1 polished bottom bracket into 68cm wide english-threaded steel bike. It was probably a 10-15 year old new-old-stock, so I dissassembed/cleaned/re-greased it. It appears to be an adjustable cup style model with both needle bearings for radial loads and angular contact ball bearings for transmitting thrust loads. Also external lock ring on the NDS cup (tolerates variance in shell widths?). To be used with FC 7700 39-53 double crank. dropouts are 130mm apart. Assuming the drive side cup doesn't necessarily bottom out, what factors and limits should I try to obtain?
Like: Specific clearance between the closest chain ring approach to the DS chainstay? Start with a distance X from bottoming out the DS cup, build out the rest of it, see where the chain rings end up then adjust? Shoot for an optimised big chainline across the cassette? Where ever the NDS cup locates the spindle? Have never wrenched this combination before, and don't want to end up with a ham-fisted result. |
[strike]7700 is an external-bearing crank, meaning it doesn't use a bottom bracket in the classical sense, just two bearings that screw into the tube.
Where did you get the idea that an Octalink BB has any relationship to either your existing setup or the 7700?[/strike] And how the heck are we to opine on chainstay clearance when you don't say what frame you're using ? |
Well, the bottom bracket is a Dura Ace 7700 v1 octalink. It's interchangeable (I think) with the 105 and Ultegra octalink v1. Which is a Shimano proprietary (JIS 2 degree?) tapered 8-tooth spline spindle. Each of the screw-in cups contains a set of needle roller bearings and a set of angular contact ball bearings. They are not cartridge bearings. It seems after seal removal, those can be removed from the cup and replaced or cleaned, regreased, and replaced as I did.. Both bearings on both sides are caged, and the spindle has removeable hardened races that set the position against the ball bearing axially. With the other parts in place, as you tighten the Non Drive Side cup into the bottom bracket shell it seems as though you can set the play or the preload against the angular contact ball berarings - also seems like you could go too far and bind it up. When the bottom bracket is fully installed, the bearings will be locating the spindle inside the bottom bracket shell. To me, that makes it an old-school adjustable internal-bearing crank. I thought external bearings actually locate the rolling elements of the bearings outside the confines of the bottom bracket shell for better resistance to radial loads (more precise positioning or ability to use a cheaper bearing?), and usually have the spindle integrated into the Drive Side crank.
The frame is my '92 Miyata Team steel road racing bike that I am building as 9-speed.Dura Ace. As noted 130mm dropouts on rear axle, 68mm wide English threaded bb shell, was a version of 7400 Dura Ace 8-speed when it was sold as a complete bike - but this was frame/ forks only. My impression is bottom shell can flex laterally somewhat more than other heavier steel bikes I have, so maybe I'll need more clearance than usual between the chainrings and chainstay and the crank arm and chainstay? :eek: |
Ooops, sorry. I got my numbers mixed up. 7700 is indeed Octalink. I should know that since BB-7703 is what I use on my road bike. Anyway, back to your question.
Correct, BB-7700 is not sealed. (7703 is) I have to give the standard answer on chainstay clearance: Try it and report back. Every frame is different. We also appreciate bike pr0n. |
From what I can tell reading Shimano SI, you install this like all 3 piece adjustable BB ie. Fixed cup (DS) goes first to torque spec then adjust for play from the NDS cup/lockring.
http://techdocs.shimano.com/media/te...9830646804.pdf |
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