Bottom Bracket ?

You need to know the shell width (width of the cylindrical part of the
frame that the bottom bracket fits into).

You also need to know the THREADING of the bottom bracket (French,
Italian, or English/ISO). If the shell is 70 mm wide, then it is
Italian. If the shell is 68 mm wide, then it is either French or
English. To figure this out, you have to figure out which way you turn
the cup to unscrew it. For more details, see this table of bottom
bracket threadings: http://www.sheldonbrown.com/gloss_bo-z.html#bottom

Hopefully you have English threads, those are the current standard and
are technically superior. A new square-taper sealed cartridge bottom
bracket should cost you $10-$30. If you replace the bottom bracket,
you'll have to replace the cranks with modern cranks as well.

So, when buying a new bottom bracket, you'll need to know: shell width,
threading, and spindle length. The appropriate spindle length depends
on the cranks that you get.

Dan Lenski

In article
<[email hidden]>,
[email hidden] says...

Quoted message said:

You need to know the shell width (width of the cylindrical part of the
frame that the bottom bracket fits into).

You also need to know the THREADING of the bottom bracket (French,
Italian, or English/ISO). If the shell is 70 mm wide, then it is
Italian. If the shell is 68 mm wide, then it is either French or
English. To figure this out, you have to figure out which way you turn
the cup to unscrew it. For more details, see this table of bottom
bracket threadings: http://www.sheldonbrown.com/gloss_bo-z.html#bottom

Dan

Thanks for the detailed inforamtion.

m alexander

m alexander said:

I have an old common market bike from the 70s that I am
currently riding. It has a cottered crank and the whole
bottom assembly is approaching worn out.

I would like to put in a modern bottom bracket.

Keep in mind that if you replace the BB with a modern sealed cartridge
unit, you'll have to get new cranks as well (because a cottered crank
won't attach to a square taper bottom bracket or any other modern BB
spindle).

Quoted message said:

My question is what measurements do I need to determine
whether a modern bottom bracket would fit?

You need to know:
* the shell width (width of the bottom bracket shell in the frame)
* the threading (English, Italian, or French)
* the spindle length and type (this depends on the cranks you use)

The shell width will probably be 68 mm or 70 mm. If it is 70 mm it is
Italian threading. If it is 68 it could be either English or French.
Basically, the way to tell the difference is by the direction of the
threads on the right-side cup. But as a practical matter, if it's made
by a French company it's French threaded, if it's anything else then
it's English threaded. See
http://sheldonbrown.com/gloss_bo-z.html#bottom for the details...

English threading is the standard now, and you can get sealed cartridge
units with a square taper spindle for as little as $10 online.

Dan