I have a 1972-ish Sekine, but am unable to take it apart until next week when tool gets here. Is there anything I can measure or look at from the outside to know which BB to order?

Bottom brackets for tapered BB axles are hit and miss, especially for cranks that have a lot of miles or removals in their history, So no one can give you a guaranteed BB length that will give you the right chianline. Best approach - when those tools come, take off the cranks, measure the spindle length and asymmetry. (In those days the drive-side was always longer.) You also need to know the taper. I'm guessing JIS, the Japanese standard, but I don't know if it was universal there then.

One approach you can take without leaving the house - buy your best guess Shimano cartridge BB. (I'd match the driveside length and go from there. Shimanos are symmetrical so the same DS gives you a longer total spindle. Now, install the Shimano, mount the cranks and measure the chainline. If good, you're done. If not, you know what you need. (Now, not all BB manufacturers are rigorous on tolerances, Spindle taper is very shallow so small differences make real changes in chainlines. Shimanos are consistently right on. So are Phil Woods (the very expensive custom level BBs made in San Jose. I"d guess Sugino next but I haven't done a side-by-side comparison. I simply use Shimanos as measuring tools and order Phil Woods but that is expensive and not everyone's cup of tea. (and the sad truth - those of us old enough to be able to justify spending that much are also old enough to be completely unable to wear them out. We don't have enough miles left. But one asset that could sway the balance - they are simply gorgeous! They come out of the box looking like the finest medical equipment.

Ben (collecting Phil Woods for future generations)

Are you talking something like the Shimano UN55 square taper? I have a Sugino RD2 crankset I would like to use with it if possible.

Here is a link to that crankset. It lists the recommended length and taper. This is where I would start. Generally the crank dictates the spindle length, not the bike. Of course, depending on how your wheels are dishes things can change.

If you have any calipers you can measure the current spindle length even while it is still on the bike. I would build it up with what's on there, check your chainline, and then see if/how badly it is off. From there you can do some simple addition or subtraction to find the right length.

https://www.treefortbikes.com/Sugino...30mm-alloy-RD2

Why do you need a new bottom bracket? If the current one isn't pitted the simplest thing to do is simply clean it and install new bearings and your good for another few years, unless of course you ride in adverse weather a lot.

Missed point: this is a Sekine, has a 70mm bottom Bracket shell. Don’t use a 68 mm unit on it.

+1 this. Despite the 70mm shell, it is English thread, not Italian. One of the cases demonstrating the unreliability of using shell width to guess thread spec.

If the current bottom bracket is in reasonable condition, why bother replacing it? If it does need replacing, look for a code on the spindle like "5N" or some such. Find a replacement spindle with the same code. Chances are, the cups will be OK; spindles always wear out first. If you do have to replace the whole thing, finding a suitable modern cartridge can be a matter of trial and error. Most English thread cartridges are designed for 68mm shells and may not work in a 70mm shell. A 73mm MTB cartridge might work with spacers in the proper places to get a reasonable chainline. Good luck!

Never heard of that issue! Couldn't they use an Italian length spindle with the English cups, since the same versions of BB axles that have English OR Italian threads usually deviate by 2mm?

I guess the OP could face each side of the BB of 1mm? Eek.

Sounds like what we called a Mexican bottom bracket because this is what Acer-Mex, Windsor used to do.

I was mostly concerned with the crankset I have to use not fitting on it

So the 70 mm bottom bracket shell is one issue. Also the taper on the spindle might be 3 degrees. That's why I didn't replace the crank on my Sekine SHS 271. I just overhauled the BB and kept the original crank.

Ugh this is what I was worried about, the frame and paint are mint but I can't really use any of the components on there.

Nah, this is easy. If all you have is a frame and fork, then that is really easy. Just get a 73 mm square taper BB and a pair of 1.5 spacers. Everything else is standard.

These are really nice bikes. I really like my SHS 271 which I use primarily as a lock up bike. The bike rides great. I just wish I could track down one of those awesome Sekine pie plates.

Thanks for the info! Sorry I am fairly new to all this. So the bottom bracket is still intact and I have a Sugino RD2 crankset I would like to use ideally, but from what I am reading the taper will be wrong? How do I address this?

I have a couple of bikes with that weird English-threaded 70mm bottom bracket shell. A 68mm cartridge bottom bracket can be used as long as the left-side cup doesn't have a lip/ledge on it. That lets the left-side cup keep threading into the shell until it can mate up with the cartridge unit. You'll have to plan on the crank sitting 1mm further to the right than if you had a 68mm shell.

Here's what it looks like from the left side when it's all back together:

Wait until you have the bike, take some measurements, and post some pics. We'll talk you through this.

I think the bike is quite likely to have a 70 mm english threaded bottom bracket but you never know until you measure it.

The tapers on the spindle may or may not be 3 degrees since that is true only for some of the cranks that came on Sekines like mine.

This won't be hard but you may have to install a new bottom bracket.

What crank do you intend to use with it?

(edit) Ah, I see you want to use a Sugino RD2. You should be able to make it work with the existing cups by using a track spindle designed for a 70mm shell.

3° taper spindles are pretty rare and AFAIK were only used on a long out of production SR Silstar crank. If that's what you have, the 3° spindle will be too wide to fit a crank designed for a 2° spindle; the mismatch will be obvious. In that event, you could replace the 3° spindle with an appropriate size 2° spindle. I'd test-fit the RD2 onto the current bottom bracket and see how the chainline looks. If the ring sits too far out (because the spindle was designed for two rings rather than one), you can reverse the spindle to bring the ring closer in. Otherwise a track spindle for a 70mm shell should work.

OR... you could have the BB she’ll shaved down.

that’s what I jokingly suggested above, but the crank and spindle taper might still be an issue?