Bottom Bracket Info  (Jobst Brandt  jobst_brandt@hplabs.hp.com)

The four kinds of BB threads in common use today are Italian, British,
French, and Swiss, possibly in that order of occurrence.

           Diameter   Pitch    Right Left Cup
           --------   -----    ----- -----
Italian    36mm   x   24F tpi  right right        tpi (threads per inch)
British    1.370" x   24F tpi  left  right
French     35mm   x   1mm      right right
Swiss      35mm   x   1mm      left  right

Unless there is something wrong with the right hand cup it should not be
removed but should be wiped clean and greased from the left side.  The
thread type is usually marked on the face of both left and right cups.
Swiss threads are rare but if you have one it is good to know before
attempting removal.

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: lifespan of a BB?
Date: 3 Dec 1996 22:51:07 GMT

Peter Guyton writes:

> When do you toss a bottom bracket?  I have a late '80s Dura-Ace BB
> (old style ball bearing races, hollow steel spindle) and seems to be
> fine but it's got to have 20,000 mi on it or more.

The type of BB spindle you describe usually develops a hole in the
bearing race that is clearly visible when you clean and lubricate it.
However, a rider who puts a lot of sprinting weight or climbing in big
gears should be aware of spindle failure that cannot be detected
reasonably before it occurs.  The fracture occurs inside the press fit
of the crank and is not exposed for inspection.  If it fails while you
are standing, you fall.  It is usually the left end that breaks off
because it is loaded in bending and torque at the same time while the
right end is loaded by bending or torque but not at the same time.
With right hand traffic, this throws you under the wheels of passing
traffic.

> As I look in the adjustable cup, I can see a slight ring of
> discoloration where the bearings contact the cup.  I can't really
> feel an indentation (although there appears to be one) but it is a
> clearly visible ring. Does that kind of visible wear indicate that
> this BB's time has come and gone?

Your bearing sounds as though it has a good wear pattern, assuming it
is a fine milky finish.  Check the balls for failures and replace the
set if any are crumbling.  I choose to change out my spindle about
every 20000 mi just because I have broken a couple and don't want it
to ever happen again.

I sense that you are interested in buying a new BB anyway, so you
should probably have a look at the new Shimano tubular spindles that
have a substantially better failure strength.  I know nothing about
how weather proof they are but they are on my list of things to
consider.

Jobst Brandt      <jbrandt@hpl.hp.com> 

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: French/English threadd BB
Date: 17 Dec 1996 17:41:49 GMT

Craig Massie writes:

> My friend bought a Peugeot and has since discovered that the
> previous owner may have threaded an English thread bottom bracket
> into the presumably French-threaded shell.  Two questions:

> 1.  Is the shell likely French thread?

Yes.

> 2.  What can be done at this point to replace the bottom bracket?  A
> local shop could not remove the Shimano Ultegra cartridge bottom
> bracket.

It is possible that the wrench flats on the right hand cup are
insufficient for removal, especially if it is the wrong thread as you
suspect.  There are some excellent high priced tools that can remove
almost any right hand cup, however.  English treaded BB cups usually
are specifically marked for identification "1.370x26 TPI" so that
should not be a mystery.  If the left cup is also tight, it requires
the grinder removal routine.  With a Dremel Tool grind through the cup
and even into the BB shell if necessary at one place.  The cup can
then be folded inward with a punch and hammer to be removed.

Jobst Brandt      <jbrandt@hpl.hp.com> 

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: Why are pedals screwed in backwards?
Date: 29 Aug 2000 23:13:28 GMT

Steve Freides writes:

> English bottom brackets (and most these days are English)  to work the
> original poster thinks they should; the drive side is reverse threaded
> and the left side isn't.

That's a complicated one because the precession is slight enough that
the right hand cup usually remains in place, even with a right hand
thread (if tight).  The odd part is that the rotating load is not
really present although part of it is.  The load is generally downward
from the right pedal with chain force to the rear about twice as
great when the right pedal is forward going descending.  When the left
pedal descends forward, chain tension is also at its greatest so the
right cup sees two large rearward pulls superimposed on one down force
and a lesser up force resulting in no true rotating load.

I've ridden for years on right-right and left-right threaded BB's and
have not had one come loose, although I feel better about not
tightening the right cup to the point of sensing onion vapors in the
eyes, just to make sure it doesn't come loose.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: Why are pedals screwed in backwards?
Date: 30 Aug 2000 15:36:48 GMT

Robin Hubert writes:

>> I've ridden for years on right-right and left-right threaded BB's
>> and have not had one come loose, although I feel better about not
>> tightening the right cup to the point of sensing onion vapors in
>> the eyes, just to make sure it doesn't come loose.

> I usually understand most everything you say but, what is the
> euphemism here?  Would that indicate crushing force?

Exactly.  The kind where you put the Campagnolo bracket tool in a
large vise and use the frame as leverage as you rotate it about the
vise.  This is a common procedure in better bike shops assembling R-R
threaded BB's.  Done at home with a 14" BB tool, this practically
brings tears to the eyes.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: Dumb question - Help needed
Date: 22 Mar 2001 16:16:50 GMT

Malarkey Mulligan writes:

> Aren't the loads on a rear hub potentially higher? A small chainring
> means the chain tension can be several times body weight.

They are probably about the same, judging from incidence of bearing
failure in which inner races or balls fail.  There is more to the
bearing loads than just the input force.  The crank spindle has its
"cup & cone" orientation reversed from what it should be for its
loading, besides having large leverage with the pedal being outboard
of the narrow bearing spacing that is less than that of a rear hub.
To make up for that, the smaller diameter of the rear axle cone
increases its stress.

Jobst Brandt      <jbrandt@hpl.hp.com>