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Is there a bottom bracket cartridge that will work?

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Is there a bottom bracket cartridge that will work?

Old 04-29-19, 04:43 PM
  #26  
repechage
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Ditch the spacer on the drive side, add it to the other side if you must.
I think though that the chainline is all out of whack, why it wont shift.
As there is no chain, what you need to do is get a 24" long straight edge, a framing square at hand?
position it against the inside surface of the large chainring, extending over the cogs, the backside of that square should be essentially at the resting over the middle of the rear cogs, no matter the number of them.
I bet it is to the outside, that difference, is the amount closer the drive side crank needs to be to the centerline of the bike.
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Old 04-29-19, 06:06 PM
  #27  
mmcc73
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The chain line was indeed pretty bad. I removed the spacer from the drive side and put it on the non drive side (BB wouldn't thread all the way on my 66mm shell without it). My front derailleur now seems to have enough range to move the chain to the big chain ring, based on visual analysis. However, the line from big chainring to rear cogs (there are 5) hits between the smallest and second smallest cogs.

So, not optimal. But maybe good enough?

If not, I could get another UN55 with a 118mm spindle (I'm currently at 122.5mm). I think I have 2mm to spare on either side.
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Old 04-29-19, 06:55 PM
  #28  
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I always thought the "big chainring" rule applied only to doubles, that with triples, you line up the middle chainring with the middle cog. Is that about where you are?
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Old 04-29-19, 07:04 PM
  #29  
mmcc73
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Originally Posted by madpogue View Post
I always thought the "big chainring" rule applied only to doubles, that with triples, you line up the middle chainring with the middle cog. Is that about where you are?
I have a double.
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Old 04-29-19, 07:08 PM
  #30  
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^^^^^ Duh, as the photo above, which I COMPLETELY ignored, clearly illustrates. Ooopsieeee.....
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Old 04-29-19, 07:44 PM
  #31  
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Originally Posted by ryansu View Post
Sometimes working on vintage bikes is like a story problem from middle school math Jimmy has 3 bottom bracket spacers, a cartridge BB and an BSD threaded BB shell, how many beers will it take before Jimmy makes his bike work again? Show your work.
Oooh, this is math I can solve!

All of the beers. Duh.

Here's the work shown:
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Old 04-29-19, 08:50 PM
  #32  
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^^^^^^ Hmm, whenever I try to solve that kind of math problem, my ability to do math gets worse, and worse, and.....
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Old 04-30-19, 02:09 AM
  #33  
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I would go with a 115mm bottom bracket, and no spacers, assuming your pictured fitment was with the crankarm actually torqued onto the spindle.

It looks like there is a lot of clearance to the chainstay, and changing from the 122mm bb to 115mm will only move in the drive-side crankarm 3.5mm, about an eighth of an inch!
From there, the option would remain to add a drive-side spacer, but not so thick as the one you had on there.

The left-side bb cup doesn't have and doesn't need a real flange on it, it is supposed to bottom out against the cartridge inside of the bb shell, NOT against the left-side face of the bb shell (or the bb cartridge would be left unsupported on it's left end).
So don't add any spacer on the left side.

Your chainline preference really depends on whether you favor use of the small or large chainring. If you favor the big ring most of the time, then the shorter spindle is the better choice as long as the chainrings still clear the chainstay and as long as the front derailer can still pull the chain sufficiently inward with authority sufficient to reliably shift down under at least some pedaling force.

It was very common for lower-to-mid level bikes to have a relatively long chainline dimension as sold, likely because so many beginning riders were unfamiliar with accurately moving their shift levers while riding, with both levers often left in the full-forward position where they couldn't slip and cause chain-grinding noises. So on these bikes that I will ride, I eventually replace the bottom bracket with one that is considerably shorter than the one fitted at the factory.
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Old 04-30-19, 06:05 AM
  #34  
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Originally Posted by mmcc73 View Post
Thanks - though I don't know what "offset DS" is. Would you mind explaining that term?
offset on the drive side.
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Old 04-30-19, 06:46 AM
  #35  
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Originally Posted by mmcc73 View Post
The chain line was indeed pretty bad. I removed the spacer from the drive side and put it on the non drive side (BB wouldn't thread all the way on my 66mm shell without it). My front derailleur now seems to have enough range to move the chain to the big chain ring, based on visual analysis. However, the line from big chainring to rear cogs (there are 5) hits between the smallest and second smallest cogs.

So, not optimal. But maybe good enough?

If not, I could get another UN55 with a 118mm spindle (I'm currently at 122.5mm). I think I have 2mm to spare on either side.
I would consider that chain line way off. The spindle is too long. Donít eyeball it, measure it.
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Old 05-14-19, 04:03 PM
  #36  
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Originally Posted by repechage View Post
I would consider that chain line way off. The spindle is too long. Donít eyeball it, measure it.
Measure, eh?

Measure I did, and ended up getting a 110mm spindle. The inner chain ring just barely clears the chain stay, but it does clear, and the chain line looks way better.
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Old 05-14-19, 07:24 PM
  #37  
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Good call there, I always try for the shortest chainline that still allows the front derailer to downshift with authority!

And if the driveside crankarm ever drifts up the taper, you can just add a 1mm steel fixed-cup spacer.
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