BB Replacement for old Sekine
 

Thanks to helpful posters I have discovered the following on the bike: 70mm BB 132mm spindle , English threaded. The parts can't be reused. One option is obviously to find a decent condition old part or donor bike with the downside being time and no guarantee of condition.

The other option is to use a 68mm cartridge bb, I presume with the longest 127mm spindle, and then get a matching crank that will work with the new rear flywheel.

My question here is primarily what BB would work best and what are the crank options?

Something like this?

The OP mentioned a 70mm shell width. Today English BB units are either 73mm or 68mm shell widths. One could get the 73 width and with spacers center (or not depending of actual ring/stay clearances needed) the wider BB within the 70 shell. But I would not get a 68 shelled BB unit as the LH retaining cup might not fully seat on the rest of the BB body.


One might also remove a mm or so from each side of the shell and reface it to a common 68mm width. Or one might remeasure the shell width and see if a mistaken initial measurement was done.


While many cranksets have guidelines for spindle length and chain line results I've found when working with fringe or odd situations there's no substitute for the trial and fit method of figuring out the best combo. This is one reason that a $25 shop install charge might be a good value. It only takes one BB return to get close to that amount of cost... if the source is willing to take back a previously installed BB at full credit. Andy.

I'd use a Shimano 73mm bb with 1.5mm spacers on the chain ring side of the bb. Hopefully the 127mm is wide enough. Or buy some new cranks too.

I talked to one local LBS and they seemed a bit skeptical but said to bring it in and they'd take some measurements and let me know there thoughts. I'm going to try one other where I know the guy's been around longer so he may have worked on something like this.

I talked to the second LBS where they are more experienced. It seems like a cartridge BB should work but it's a little unclear whether one would go with a 68mm or a 73mm, they seemed to think you'd pick the new crank first and go from there.

Hopefully I ca dig up some NOS with T-Mar's help.

Why a new crank? Try the old one on a new BB and see if it fits.

The Spindle taper on the original is 3 degrees not 2.

I've never seen or even heard of a 3 deg taper spindle. Learn something new every day.

Ok, so if you're getting a different crank, I would find the crank first, then the spindle length that give that crank the proper chain line. Different model cranks use different spindle lengths to get the proper chain line.

http://www.sheldonbrown.com/bbsize.html

I think the Tange LN-3922 BB I put in my Paramount has a left-side "cup" with no shoulder, so it can go as far in as you've got threads. I'm out of town and I can't look at it. I've never had to use spacers with any BB, so I can't help there.

Somehow between ebay, Sheldon, and Andy you should find what you need.