EGBigelo

I bought a 1989 Schwinn 564 and I've torn it all down and cleaned/degreased everything. I want to replace the bottom bracket with a sealed cartridge unit. My bottom bracket is a 68mm. My spindle measures 116mm (it's branded as Shimano 3A MK). I can't seem to find a 68 x 116 that got decent reviews.

Does a couple millimeters matters? Could I get by with a 68 x 117 or a 68 x 118?

fietsbob

Opinions are No substitute for trying it..

Shimano type cartridge bearing BB are so cheap why struggle finding the increasingly rare loose ball ones
they are replacing

Andrew R Stewart 

Is the old BB axle still accessible? If so then you could measure it to discover if it's an asymmetrical or symmetrically dimensioned. By this I mean the distance from the bearing races to the axle's ends.

If both sides are the same length then the axle is symmetrical. Most current cartridge units are symmetrical. So in this case if you were to use a 116mm axle length BB the rings would sit about where they did with the old unit.

But if the old one has a longer RH bearing to end length, then the left side, different math is needed to duplicate the chain line. Take the end length difference and add it to the overall length to get what a modern symmetrical unit should be. Example might be if the old axle has 2mm more bearing to end length then the LH end does. So 116 plus those 2mm is 118 and the new symmetrical axle length to retain the approximate chain line as before.

https://sheldonbrown.com/bbsize.html is a link to a dimensional chart to better explain this stuff. Andy

Bill Kapaun

A 3A has the DS offset 3mm longer than the NDS.
30.5<>52<>33.5
Your "symmetrical equivalent" would be 52 + (2*33.5) or 119mm.

Bigbus

Note that because you will be going from asymmetrical to a symmetrical BB the LH crank will be farther out from the frame also. This doesn't bother most people because the difference is minuscule. But some people might find it off-setting...
As far as reviews go, I haven't seen anything but good with regards to the Shimano Un-55. I have first hand experience with the UN-26 and I love it. I got tired of replacing bearings and constant adjustment and greasing. The 26 has plastic threads and caps while the 55 is all metal. Both are good BBs in my opinion.

I forgot to add- Make sure you duplicate your chainline and let the LH land where it lands. I ended up having to shim out my FD to get the chainline back because the BB I purchased had too long a shaft, and I went shorter than the recommended guide. FWIW

EGBigelo

Thanks everyone. UN-55 is what I'm going to go with.

But, I have a lot of learning to do first. I didn't even think about the asymmetrical scenario, and the chainline. I'm not new to working on my own bikes, but just the basics.

I appreciate all the advice!

ThermionicScott 

3A is actually 32-52-33.5 for about 117.5mm total. A Shimano UN55 in 118mm length would give you almost exactly the same chainline for $20 and they get good reviews from me.


(Showing my math: from the centerline of the frame, the 3A is 26+33.5=59.5mm to the end of the drive side. The 118mm UN55 is 34+25=59mm.)
https://web.archive.org/web/201010220...ttom-brackets/

Bill Kapaun

Your source for the 3A dimensions?
Mine shows otherwise. See the pdf.

If you read the link you posted, they only state the DS length relative to the other models they had in stock.
They make a disclaimer about other brands.

ThermionicScott 

That's interesting. My first step was to measure an actual Shimano 3A spindle from my collection ("LJ"date stamp) and it came to a hair under 118mm total, with the drive side about 1.5mm longer than the non-drive side.

The Shimano 3L spindle in my collection measures 116mm (as stamped) and measures 32-52-32, contradicting the YJ chart.

I think these spindle designations weren't always consistent between brands. Sheldon linked to that document of Indian standards, and some of them don't match what are in his table, or what we're used to seeing from Shimano/Sugino.


P.S. I'm not sure what you think I'm missing about the blog post. They measured Sugino/Shimano cartridge bottom brackets, and so I feel pretty confident in being able to compare the two products and make a recommendation.

andrewclaus

If there's a bike co-op in your area, they will have a have a bin full of salvaged cartridges. There you can try several sizes, see what works.

Andrew R Stewart 

To tangent on listed dimensions and brand/production natch drift. Yes, it's been my experience too. Some dimension drift from brand to brand and from batch to batch has been the case for decades.

You know way back when these asymmetrical axles were the rule we didn't get too upset at a mm or three of chain line shift. These days so many people get upset at a mm of "wrongness". Oh well, just because you can measure something doesn't mean it matters always. Andy

Bill Kapaun

As much as we would like, measuring to the end of the spindle is not the correct way to measure.
You have to measure to a reference point on the sq. taper where it's a specified dimension.

Visualize the taper extending to a point.
You'd have a mighty long spindle, but the crank is still going to have the same chain line.

ThermionicScott 

Agree that that's a concern. I think measuring to the ends is the language most of us are used to speaking, right or wrong, and that's the implied measurement when buying 'em.

Without shelling out $40+ for JIS D9403, I'm gathering online that the end of a JIS spindle is supposed to measure ~12.63mm thick. I'll bust out my digital calipers when I get home and see how things measure up.

krecik

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fietsbob

whos to care, if the bike goes forward .. it does..

krecik

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