CrowSeph

Hello!
I'm converting a 90' frame into a gravel-monster bike.
Actually in the build setup there is a square bottom bracket, for now it is okay but in a future i want to swap into a bsa type.
There are two problems that i think may occurs.

1- Treads on the frame probably are shorter than the cups itself.
2- What about the axle? are they available in shorter size? with a square taper there is not really a problem since i can fit a longer type.

if you need further information:
- Rear hub is 142mm
- 10s cassette
- i don't have the frame right now, but i have a similar frame laying around. I can measure the bottom bracket housing for an hypothetical calculation.

dedhed

BSA aka English isn't a "type" but a threading standard of the BB shell.
https://www.parktool.com/en-us/blog/...identification

CrowSeph

thanks for correcting me, for bsa i was meaning this type of "cups".

grumpus

BSA stands for Birmingham Small Arms, originally a gun manufacturer that also made bicycles, motorcycles and other vehicles and industrial parts. BSC stands for British Standard Cycle, referring to thread dimensions used by most British cycle manufacturers (but not Raleigh) and many others for most of the 20th century. The ISO thread standard for bottom brackets, introduced in 1989, has the same thread pitch and angle as BSC but 1.375" as opposed to 1.370" - the difference is that ISO threads are truncated slightly less than BSC, so a BSC bottom bracket will fit an ISO shell, but not necessarily the other way around (2.5 thou/0.06 mm on the radius is small enough that it will usually fit with no problem).

TLDR: BSA is a company, BSC is a thread standard, but if you call it BSA people will mostly know what you mean; likewise it could well now be ISO not BSC but they're mostly interchangeable.

grumpus

That's external bearings on a ISO threaded cup, to fit a wider spindle than internal bearings allow - typically 24 mm as used by Shimano Hollowtech II

Kontact

That's called an external cup BB, and they are used with specific cranks. They should work on bikes with English/BSA threads as that is what they were designed for.

You have a '90s frame with a 142mm rear triangle spread? That seems unlikely. 142 is generally through axle width - which didn't exist in the '90s.

grumpus

I don't understand what these points are saying - can you elaborate?

CrowSeph

frame has been modified. 142 is the new lenght

CrowSeph

sure, i learned english by myself and sometimes is not very good.
i'll try again to explain.

ofc those are just assumptions
- bottom bracket's shells probably have a longer tread length than the classical one.
- if i fit those sheels plus some spacers, i will be able to use an hollow tech axle? there are possibility that the axle will be longer and do not fit properly?

Kontact

The frame BB has longer thread or the cups have longer thread? Either way, the cups should fit. Sometimes the threads in the frame don't go deep, but it doesn't interfere with the cups.

You can't use spacers unless they are necessary to convert a 68mm BB shell to work with a crank intended for a 73mm BB shell - like an MTB crank.

oldbobcat

Perhaps a photo of the bottom bracket shell of the frame and the crank that you wish to put on it would be helpful.

dedhed

The external BB cups in your photo will thread without issue into a 90's frame. But you have to verify if the frames BB shell threading, either English or Italian depending on what frame although most likely English. You also have to measure BB shell width 68mm road, 73mm Mt. The cranks that fit those are 2 piece and axle width is fixed and come in 2 diameters, 24mm Shimano and 30mm FSA etc and the BB bearings have to be sized accordingly.

Square taper BB come in either cup & cone or cartridge with varying axle widths as well as offsets. Square taper cranks require the correct (or "close enough") length and/or offset to position the crank and rings to clear the frame and give correct chain line.

Given your 142mm proposed spacing what is the proposed chain line going to be?
https://www.parktool.com/en-us/blog/...nline-concepts

CrowSeph

frame has been sent to a local framebuilder for further modification, when is ready i'll add some photos.

CrowSeph

thanks for sharing this interesting link.

Kontact

Maybe your framebuilder can explain what components you need?

CrowSeph

oopsy, i meant the local welder!