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Bottom Bracket Question

Old 05-10-20, 06:57 PM
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Kactus
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Bottom Bracket Question

I am looking to put an IRD compact crank (the hills keep getting steeper) on my '71 Paramount. The IRD crank arms are JIS taper vs, the Campagnolo ISO taper of the spindle on there now. The stock Campagnolo spindle is 113mm with an offset towards the drive side. Most of the replacement BB's I've seen are symmetrical, without the offset. It looks like I can have a Phil Wood BB made with an offset, but I don't want to go to the expense of having everything done for one if I can avoid it.

Has anyone done a similar swap? If so, what did you do for a bottom bracket?
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Old 05-10-20, 11:39 PM
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merziac
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I know not everybody operates this way but has worked fine for me for 45 years.

Many here do subscribe to it.

Mix and match, if the tapers are that different then the arm will sit different on them, never seen a mismatch so great that it didn't work once seated and tightened properly.

Shouldn't be able to hurt the new crank and certainly not going to hurt the hardened spindle.

All that being said I do know we had a thread very recently that showed an arm that was still quite outboard when seated, I have never had one that far off so...

JIS, ISO, Phil, Campy, Shimano, Sugino, once the crank has been seated on the different spindle and ridden, the proof is in the pudding, if it works and stays tight as mine always have, you're good to go imho.
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Old 05-11-20, 04:33 PM
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Couldn't find the info on the IRD site, may just looked in the wrong place, but Boulder bicycle sells the IRD Defiant compact cranks and says on their site that 118mm JIS is the proper length but that 115mm will work.

It's not possible without measuring, AFAIK, to see exactly how the IRD crank will fit on your Campagnolo spindle because the Campagnolo spindle is not symmetric (which makes the Campagnolo 113mm seem longer) and the JIS crank will slide farther onto a Campagnolo spindle because the Campagnolo spindle is a bit smaller at the end (which makes the Campagnolo 113mm seem shorter). Without checking and measuring, my WAG is that you will be happier with a longer spindle. IRD makes BBs that will work. So, likely, does Shimano. If you use a real JIS BB, you won't have to worry that maybe the taper on your BB is too short. Or, check fit the new crank on the existing spindle and check for bottoming out on the spindle and check chain line.
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Old 05-11-20, 06:45 PM
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Originally Posted by Kactus View Post
Has anyone done a similar swap? If so, what did you do for a bottom bracket?
I did the opposite recently, using an ISO crank with a JIS spindle. I read what Sheldon said about the crank sitting 4.5mm further out, but really just wanted to make sure the small chainring cleared the chainstay and that my chainline was normal.

I borrowed a cartridge bb from a friend to check length. I then grabbed the lightest Taiwanese cartridge bb from ebay that $30 could buy. I'll probably never need to service it again. <sadface>
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Old 05-12-20, 04:07 PM
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I tried the IRD crank on the stock Campagnolo spindle and it bottomed out in the ISO taper before tightening. I put in a 118mm cartridge BB with a JIS taper and it's much better. The chainline seems to have moved about 1 - 1.5mm further outward; easily within the range of the Record front derailleurs adjustments and not visually notable.

Thanks for the advice! I'm sure my body will be much happier climbing any hills.
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