comradehoser

So, I'm doing some work on a friend's fixed-gear conversion.

She is running Sugino RD 2s on an old-school Italian-thread Shimano 6600 square taper bottom bracket w/ an NJS dura-ace spindle and caged bearings. The BB shell is 70mm, and the spindle also reads 70. BB cups are nice and tight. So far, so good.

The issue is that the cranks get nowhere near to proper tightness before they bottom out on the BB cup faces. Is this possibly due to a taper standard mis-match? Or is it due to a too-short BB? Or something effed with the cranks?

The 70mm shell bike is no longer an issue, because I totalled it with my fat ass (that's another story), but I'm swapping her parts over to a replacement frame with a 68mm shell and since I have to order a new BB, I want to avoid repeating the problem.

I think the Sugino cranks are JIS, and would assume the Dura-Ace bits are also JIS (unless NJS requires differently), so the bottoming-out issue is a bit of a stumper for me. Just for reference, the taper starts are just about flush with the BB cup outer edges.

Ex Pres 

NJS standard uses ISO taper for square BBs

Edited: An ISO taper will be about 12mm across the face, JIS about 12.5mm
thanks Dirtdrop

comradehoser

right.

so the JIS cranks shouldn't press on as far on an ISO BB as with a JIS BB, right? And so bottoming out shouldn't be an issue. But it is, and I'm trying to understand why. Any ideas?

Ex Pres 

The only idea I have is that you have an ISO crank - some Sugino cranks are but I don't recall the models - on a JIS taper. But you say the taper is NJS which is supposed = ISO. Or the crank's taper could be very worn. Are these cranks old?

Edit: rereading - are the cranks bottoming out on the cup face or on the face of the taper? If on the cup face but you have taper left, then you need a longer spindle.

Edit2: the 75's are ISO, so your cranks should be JIS

comradehoser

thanks for the feedback, bob. I hope retirement's treating you well. You didn't use to post up on CT, did you?

yeah, the cranks bottom out on the cup face. the end of the taper sits just inside the bb cup aperture. seems like the crank would bottom out on that too, though.

Agreed, the longer spindle is probably what is needed, but what puzzled me is that the markings seem to indicate that it's for a 70mm shell, so why the problem?

Ex Pres 

The 70mm vs 68mm spindles only differ in the distance between the bearing ridges on the spindle (Italian = 2mm longer). It doesn't have any correlation to spindle length.

You buy square taper BBs:
1. Correct taper to fit the crank (ISO/JIS)
2. Proper cup threading and width to fit the frame (ie. Italian 70mm)
3. Spindle length to match the crank

#3 is what you need to find: a specification for the RD2s

Grand Bois

You would be giving him good advice if you didn't have it backward. The J.I.S. spindle are the blunter ones.

Ex Pres 

fixed, thanks

dafydd

many low-profile cranks just don't work with cup-and-cone BBs, they're designed to recess slightly into where the installation tool fits into a cartridge BB. Depending on your seattube diameter, you probably need either a 68 X 110 or 113.

jgedwa

+1. Took me a fair bit of head scratching to figure this out on several installations. jim

comradehoser

actually, I went with a shimano cartridge BB, 68 x 107, and it barely gave me a 42mm chainline (she's using phil track hubs) with the chainring on the inside of the spider. According to some talk on the SSFG board, the sugino RD2 cranks sit a couple mm wider on a given BB than other cranks. I guess my installation bears that out

dafydd

oops, didn't catch the fixed part.