Hi guys,

Im redoing a Sekine (japanese bike made in Canada) and I wanted to change the old bottom bracket system with a sealed one. However, its a 70 mm with an english thread. Those are impossible to find (70 are always intalian thread).

What is the best solution (I would like to avoid to have it faced) to fit a 68 mm or a 73 mm ? Have someone had try any of those and what was the results ?

Thanks

Maybe there's a threadless BB (as in repair one with angled lockrings) made for a 70mm shell out there. But since I have the facers it would take about as much time to search for said BB as to face down the current 70mm to 68mm. Then I would have a lot of options now and for years to come.


If you try a 73mm one just make sure that the tread engagement is enough. Some modern BBs don't have a lot of thread on the fixed side.


BTW the Sekines were manufactured in Japan and only assembled in Canada (to skirt tariffs). Andy

You could use a Velo Orange threadless bottom bracket.

If you use a bottom bracket whose non-drive side cup doesn't have a shoulder/flange, you may be able to seat the non-drive side cup 2 mm deeper.

Some cartridge bottom brackets, notably Phil Wood, have retainer rings that are separate from the cartridge body. You can install them an extra mm deeper on each side with no problem to hold the bottom bracket securely in place. There are some bottom brackets whose cups aren't integral to the cartridge body, and you may be able to use Phil rings with them. I believe some people did this with (discontinued) Shimano UN72 bottom brackets.

Some old cup-and-cone bottom brackets had seals, if you can find a set of cups in good condition.

BEST solution is the one you don't want to do.. get over it.


A better bike shop has frame prep tools , they can use them to clean up the threads then face the shell down to 68mm

from 70 its only a mm per side.

Old bottom brackets are often asymmetric.
Put a spacer on the crankset side.

Something like this BSA Bottom Bracket Cup Spacers

Thank for all your answer.

My goal was to avoid putting to much money, that why I wanted to avoid facing and why the Velo orange is over my budget.

I heard some people fitting a 68mm deeper like you mention but I was wondering if you have thread left they will rust and after it would be a nightmare to take it out.

The space option provides by Barabaika is really good, if I make sure I have long thread enough like mention by Andrew. I will verify if it is symmetric, if yes I assume 1.5 on each side will be the best option.

Also, I never heard of threadless BB, I will look into that.

Use a bottom bracket with a plastic non-drive side cup and cover any exposed bare metal with something like Testors model paint or nail polish that won't put up too much of a fight when you need to remove the cup.

(Not nearly as ideal as facing the bottom bracket, but you're looking for cheap.)

Spacers would go entirely on the drive side. That side gets cinched down to the bottom bracket shell. The non-drive side cup gets cinched down against the cartridge body. If the NDS cup has a flange, it may or may not seat tightly against the spacer. If the NDS cup doesn't have a flange, the spacer would just fall off.

3 mm of spacers will offset your spindle a bit to the drive side, which could actually be a good thing if your crankset was designed for an asymmetric spindle. That was very common before (mostly) symmetrical cartridges became the norm. You'll have to measure your existing spindle to check.

I don't know if 3 mm spacers are commonly available, but 2.5 mm spacers are. That should be enough for you to seat a 73 mm cartridge.

The Velo Orange cartridge I linked above is a threadless bottom bracket. There are less expensive ones, but most of them have beveled flanges that are designed to seat in a chamfered bottom bracket shell. If you're going to cut a chamfered edge into your bottom bracket shell, you might as well cut it down to 68 mm.

Hi, I wanted to give the conclusion to my issue to help the next person trying to do something similar.

The challenge was that I had a Sekine bike and I wanted to change from a cotter pin crank with a loose bearing BB to a sealed BB. The problem was that the bottom bracket was American thread but with a 70 mm length which is unusual.

The solution: I bought a 73 mm Shimano bottom bracket and fit it with spacers. A 2.5mm on the non-drive side and a 1 mm on the drive side. Really simple, well made and cheap.