I have a 1960s Peugeot bike with a cottered bottom bracket that I want to convert into square tapered. I was told that this could easily be done just by replacing the spindle with a square tapered one. I measured the dimensions of the cottered spindle and found that the center, or B in this image from Sheldon Brown

was 56mm. If I buy a spindle with the middle length of 52mm, im think it would not work because the space between the bottom bracket shell and the spindle thing (dont know what its called) is too far apart for the loose bearings.

How do I solve this problem?

Buy a new french threaded bottom bracket? (or maybe just new bearing cups?)

or will the 52mm spindle work with the bottom bracket cups I already have?

First, if you decide to replace it with a
sealed cartridge unit from Velo Orange:

https://store.velo-orange.com/index.p...y-cups-26.html

I have one I just ordered for a PX-10
overhaul, and while I cannot testify with
regard to its longevity, it appears to
be a very high quality product.

If you want to simply replace the spindle,
whether your 4mm shorter spindle (between
the cone surfaces) will work depends on
how much adjustment you have to play
around with in your adjustable cup. As
long as you have enough thread left to
install and tighten the lockring after you
adjust the bearings, you're good.

There used to be a number of various
square taper spindle replacements available -
which is probably when whatever you read
was written. Now, unless like me you have
access to a pile of used parts or a bike coop,
the choices are more limited. Perhaps
someone else will post a suitable source for
a guaranteed replacement.

But if you really like the bike, plan on keeping
it for a while, and are going to replace
with a reasonable quality crankset, consider
the Velo Orange sealed unit.

You could also do it the old fashioned way and buy your spindle and cups on eBay. You'll find both Campagnolo and Shimano sets in French thread there right now. You just missed out on a T.A.

If you buy the Velo Orange unit, you'll have to use a crank with a JIS taper. That's okay if it doesn't bother you to put a Japanese crank on a French bike.

I have four French roadbikes, so I have some experience with this stuff.

I also read somewhere that someone used a italian bb spindle for this. Im not sure under what circumstances it would work but im guessing italian bb spindles have a wider center section (maybe 54mm?) and i am still not sure if it would work to replace a 56mm...

I just tested how much thread I have left on the adjustable cap after installing everything and there was 2 levels of thread left. I dont think thats any more then 2mm of adjustable space meaning I would need to have an axle of no less than 54mm wide between both ridges?

Grand Bois:
As do I , amigo. Take it from me that even the
experienced can err from time to time. Certainly
there has been a great deal written and discussed
with regard to Square taper cotterless crank
interchangeability that would be largely unnecessary
if the situation were as simple as you describe.

Besides this: https://www.sheldonbrown.com/bbtaper.html

which as a summary of practical application of available
information works pretty well, I can quote from
Sutherland's Sixth 3-5 : (sounds sort of biblical, no?)

and 3-8: While I appreciate your passion for period authentic
restoration, it can be somewhat limiting to search
continually for old parts on e-bay when what is
actually required for a repair is readily available,
albeit in a more modern format.


To organicmuch: From that same section of Sutherland's
Sixth 3-5 :

so there is an additional problem. My own feeling
(and I too own a couple of Frenchies that I enjoy riding
from time to time) is that they would be much easier to
work on if I lived in Paris. Meanwhile, I'm grateful for the
Velo Orange contribution because it is cheaper than a
Phil Wood BB and it makes my life a little easier.

Respectfully,
Mike Larmer

I found this useful piece of information from Sheldon Brown's site answering my question.
Now, 3alarmer brings up another problem with interchangability between peugeot and other parts. Am I doomed to replace the entire bottom bracket?

An ISO crank will sit farther out on a JIS spindle. This not only creates chanline issues, but can result in a damaged crank.

The simplest way by far is to buy French cups and a 118 mm spindle and use a vintage French crank. All of the old French doubles use that length.

Here's one that I converted to cotterless. I used Sugino cups and a Sugino ISO spindle marked MW-68.



I used the cottered crank on my beater Jeunet.



This one has an ISO cartidge BB made by Edco of Swizerland. Velo Orange used to sell them. I had to use it because I was unable to find the correct spindle for the triple.



I used Stronglight cups and a 118 mm Stronglight spindle on this one. I see them on eBay all the time.

I think "doomed" is putting it a bit harshly. A Velo Orange bottom bracket and compatible crank will solve all of your problems at reasonable cost.

I fully agree with 3alarmer that insisting on an authentic period restoration is a very limiting approach for a bike that is going to be used as a practical rider. If you were restoring it to be a museum piece, fine, but not if the bike is to be put to practical use.

I prefer to think of it as following the path of least resistance.

If you can find a spindle with the same B measurement, you can Use your Cups,
if they are not pitted
A,C and D are all dependent on the crank you get, and its requirements..

What part of: .
did you not understand?