Any problem running BB - UN52 or 72 backwards?

Martyn Aldis said:

The eccentric on the front bottom bracket of our tandem has been fitted
so that the unit goes in the normal (solo) way round, that is solid
thread to the right. With our cross-over drive this means the drive
side get the plastic ring and the non-drive side the solid thread.

That's not a problem in practice. Don't worry about it. You've got the
same situation in back, and the left side stresses are equal in
magnitude, despite being opposite in direction.

Quoted message said:

I can see no reason not to reverse the eccentric as the thread
handedness is just inherited from the days when the threads directly
held bearing cups. Is there any reason, internal to the sealed unit
perhaps, why I should not do this and in effect run the unit mainly
backwards?

There is a small risk that the retaining rings might tend to
spontaneously unscrew.

Since these are symmetrical bottom brackets, there's nothing to be
gained by reversing them. My advice is to use 'em as intended.

Sheldon "You're Overthinking This" Brown
+-------------------------------------------------------------------+
| The secrets of flight will not be mastered within our lifetime- |
| -not within a thousand years -Wilbur Wright, 1901 |
+-------------------------------------------------------------------+
Harris Cyclery, West Newton, Massachusetts
Phone 617-244-9772 FAX 617-244-1041
http://harriscyclery.com
Hard-to-find parts shipped Worldwide
http://captainbike.com http://sheldonbrown.com

In message <[email hidden]>, Sheldon Brown
<[email hidden]> writes

Quoted message said:

Martyn Aldis said:

The eccentric on the front bottom bracket of our tandem has been
fitted so that the unit goes in the normal (solo) way round, that is
solid thread to the right. With our cross-over drive this means the
drive side get the plastic ring and the non-drive side the solid thread.

That's not a problem in practice. Don't worry about it. You've got
the same situation in back, and the left side stresses are equal in
magnitude, despite being opposite in direction.

OK. I'm just casting around for a reason why the last unit I put in
only lasted a few 1000km while the ones on a solo go on and on.

Quoted message said:

Quoted message said:

I can see no reason not to reverse the eccentric as the thread
handedness is just inherited from the days when the threads directly
held bearing cups. Is there any reason, internal to the sealed unit
perhaps, why I should not do this and in effect run the unit mainly
backwards?

There is a small risk that the retaining rings might tend to
spontaneously unscrew.

I do not agree about this one.

With traditional cups the LHS cup is being driven one way by the ball
bearings and the RHS the other but not with the same torque. The
difference in the torque is what is felt by the whole sealed BB unit in
the modern set up and that torque must act with spindle rotation.

The outside of the sealed unit is one piece so it must all be being
dragged round with the spindle, that is, if released it would rotate
clockwise viewed from the RHS of the bike as I pedal forwards. If that
was not so, the whole bearing assembly would be providing negative
frictional drag - a nice prospect but.....

The reversed unit is, I think (or sorry Sheldon, perhaps over think ;-
)) better secured by the rings than the normal. It is only any possible
directionality in the internal assembly of the sealed unit I am bothered
about.
--

Martyn Aldis, e-mail [email hidden]
==============================================================================

On Wed, 9 Feb 2005 23:01:19 +0000, Martyn Aldis

may have said:

In message <[email hidden]>, Sheldon Brown
<[email hidden]> writes

Quoted message said:

Martyn Aldis wrote:

There is a small risk that the retaining rings might tend to
spontaneously unscrew.

I do not agree about this one.

The reversed unit is, I think (or sorry Sheldon, perhaps over think ;-
)) better secured by the rings than the normal. It is only any possible
directionality in the internal assembly of the sealed unit I am bothered
about.

Sheldon is correct, but not for the reason that you think. The torque
transmitted from the spindle by bearing drag is not the issue; the
squirm of the unit in the shell under substantial load is the problem,
and while the issue is likely trivial in a shell that's beefy, there
is a small potential for walk-out due to the slight orbital motion
imparted by pedalling. With the UN52 units I've been seeing lately,
I'd consider this a remote possibility at worst. In fact, with those,
my big issue has been that the lack of threads on the last couple of
millimeters of the right-side end leads to jamming the threads if
you're going to seat the bearing's flange against the BB shell.

--
My email address is antispammed; pull WEEDS if replying via e-mail.
Typoes are not a bug, they're a feature.
Words processed in a facility that contains nuts.

Martyn Aldis said:

Quoted message said:

Quoted message said:

I can see no reason not to reverse the eccentric as the thread
handedness is just inherited from the days when the threads directly
held bearing cups. Is there any reason, internal to the sealed unit
perhaps, why I should not do this and in effect run the unit mainly
backwards?

I replied:

Quoted message said:

Quoted message said:

There is a small risk that the retaining rings might tend to
spontaneously unscrew.

Martin demurred:

Quoted message said:

I do not agree about this one.

With traditional cups the LHS cup is being driven one way by the ball
bearings and the RHS the other but not with the same torque. The
difference in the torque is what is felt by the whole sealed BB unit in
the modern set up and that torque must act with spindle rotation.

The outside of the sealed unit is one piece so it must all be being
dragged round with the spindle, that is, if released it would rotate
clockwise viewed from the RHS of the bike as I pedal forwards. If that
was not so, the whole bearing assembly would be providing negative
frictional drag - a nice prospect but.....

Oh, that explains whe we in the repair end see so many Shimano BB
cartridges unscrewing themelves from ISO/British bottom brackets!

Why, I myself have seen more than... ... ... well, actually I
haven't _ever_ seen this happen!

Sheldon "Precession" Brown
+----------------------------------------+
| All theory, dear friend, is grey, |
| but the golden tree of actual life |
| springs ever green. --Goethe |
+----------------------------------------+
Harris Cyclery, West Newton, Massachusetts
Phone 617-244-9772 FAX 617-244-1041
http://harriscyclery.com
Hard-to-find parts shipped Worldwide
http://captainbike.com http://sheldonbrown.com

Martyn Aldis said:

Quoted message said:

Quoted message said:

The eccentric on the front bottom bracket of our tandem has been
fitted so that the unit goes in the normal (solo) way round, that is
solid thread to the right. With our cross-over drive this means the
drive side get the plastic ring and the non-drive side the solid
thread.

I replied:

Quoted message said:

Quoted message said:

That's not a problem in practice. Don't worry about it. You've got
the same situation in back, and the left side stresses are equal in
magnitude, despite being opposite in direction.

OK. I'm just casting around for a reason why the last unit I put in
only lasted a few 1000km while the ones on a solo go on and on.

I wonder if you're running your synch chain too tight?

Stresses on rear tandem bottom brackets are certainly higher than those
on solos, but stresses on front BBs should be actually less than those
of a solo, providing you're using reasonable sized synch chainrings.

I have seen Edco BBs with 3 cartridge bearings, 2 on one end and one on
the other. A setup like that could well benefit from being reversed,
but I'm pretty sure the Shimanos are symmetrical.

Sheldon "Sometimes Conventional Wisdom Is Correct" Brown
+---------------------------------------------------+
| "O, don't the days seem lank and long |
| When all goes right and nothing goes wrong, |
| And isn't your life extremely flat |
| With nothing whatever to grumble at!" |
| --W.S. Gilbert |
+---------------------------------------------------+
Harris Cyclery, West Newton, Massachusetts
Phone 617-244-9772 FAX 617-244-1041
http://harriscyclery.com
Hard-to-find parts shipped Worldwide
http://captainbike.com http://sheldonbrown.com

Martyn Aldis said:

The eccentric on the front bottom bracket of our tandem has been fitted
so that the unit goes in the normal (solo) way round, that is solid
thread to the right. With our cross-over drive this means the drive
side get the plastic ring and the non-drive side the solid thread.

Quoted message said:

I can see no reason not to reverse the eccentric as the thread
handedness is just inherited from the days when the threads directly
held bearing cups. Is there any reason, internal to the sealed unit
perhaps, why I should not do this and in effect run the unit mainly
backwards?

I don't know of any failures due to a nylon BB cup deforming
once properly installed.

--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

Martyn Aldis said:

In message <[email hidden]>, Sheldon Brown
<[email hidden]> writes

Quoted message said:

Martyn Aldis said:

The eccentric on the front bottom bracket of our tandem has been
fitted so that the unit goes in the normal (solo) way round, that is
solid thread to the right. With our cross-over drive this means the
drive side get the plastic ring and the non-drive side the solid
thread.

That's not a problem in practice. Don't worry about it. You've got
the same situation in back, and the left side stresses are equal in
magnitude, despite being opposite in direction.

OK. I'm just casting around for a reason why the last unit I put in
only lasted a few 1000km while the ones on a solo go on and on.

Quoted message said:

Quoted message said:

I can see no reason not to reverse the eccentric as the thread
handedness is just inherited from the days when the threads directly
held bearing cups. Is there any reason, internal to the sealed unit
perhaps, why I should not do this and in effect run the unit mainly
backwards?

There is a small risk that the retaining rings might tend to
spontaneously unscrew.

I do not agree about this one.

With traditional cups the LHS cup is being driven one way by the ball
bearings and the RHS the other but not with the same torque. The
difference in the torque is what is felt by the whole sealed BB unit in
the modern set up and that torque must act with spindle rotation.

The outside of the sealed unit is one piece so it must all be being
dragged round with the spindle, that is, if released it would rotate
clockwise viewed from the RHS of the bike as I pedal forwards. If that
was not so, the whole bearing assembly would be providing negative
frictional drag - a nice prospect but.....

The reversed unit is, I think (or sorry Sheldon, perhaps over think ;-
)) better secured by the rings than the normal. It is only any possible
directionality in the internal assembly of the sealed unit I am bothered
about.

Any net movement ( rare in practice) is from precession, not
bearing drag.

--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

In message <[email hidden]>, Sheldon Brown
<[email hidden]> writes

Quoted message said:

I wonder if you're running your synch chain too tight?

No problem with that here. I was wondering if the softness of the
plastic allows the axle to move back a very little on the drive side and
so increase the axial load on the bearing but I think I'm clutching at
straws.

Quoted message said:

Stresses on rear tandem bottom brackets are certainly higher than those
on solos, but stresses on front BBs should be actually less than those
of a solo, providing you're using reasonable sized synch chainrings.

I have seen Edco BBs with 3 cartridge bearings, 2 on one end and one on
the other. A setup like that could well benefit from being reversed,
but I'm pretty sure the Shimanos are symmetrical.

I'm coming to the conclusion that it may just be an odd poor example of
a normally good product or more likely that the unit was mistreated on
its way between Shimano and me. A local shop built a wheel for me using
a hub that had been submerged in a minor flood and as that shop has
folded and sold its stock, this unit could even have come through there.

Many thanks for the suggestions. I'll get a new one, fit it as
recommended and see how it goes.

--

Martyn Aldis, e-mail [email hidden]
==============================================================================

In message <[email hidden]>, Sheldon Brown
<[email hidden]> writes

Quoted message said:

Martyn Aldis said:

Quoted message said:

> I can see no reason not to reverse the eccentric as the thread
>handedness is just inherited from the days when the threads directly
>bearing cups.

I replied:

Quoted message said:

Quoted message said:

There is a small risk that the retaining rings might tend to
spontaneously unscrew.

Martin demurred:

Quoted message said:

Quoted message said:

The outside of the sealed unit is one piece so it must all be being
dragged round with the spindle, that is, if released it would rotate
clockwise viewed from the RHS of the bike as I pedal forwards. If that
was not so, the whole bearing assembly would be providing negative
frictional drag - a nice prospect but.....

Oh, that explains whe we in the repair end see so many Shimano BB
cartridges unscrewing themelves from ISO/British bottom brackets!

Why, I myself have seen more than... ... ... well, actually I
haven't _ever_ seen this happen!

Yes, I was quite wrong.

Before I started thinking about the sealed cartridge, I though I
understood why right side BB cups are better with a left hand thread but
thinking about the cartridge unit undermined my false understanding. (I
had an idea that the reaction to the motion of the balls in constant
rotation was the cause -like a planetary gear used to reverse rotation.)

I now see that the way the pedal and chain load alters during each
rotation is the key to understanding this.

Thanks for your helpful and patient responses.

--

Martyn Aldis, e-mail [email hidden]
==============================================================================

In message <[email hidden]>, Werehatrack
<[email hidden]> writes

Quoted message said:

Sheldon is correct, but not for the reason that you think. The torque
transmitted from the spindle by bearing drag is not the issue; the
squirm of the unit in the shell under substantial load is the problem,
and while the issue is likely trivial in a shell that's beefy, there
is a small potential for walk-out due to the slight orbital motion
imparted by pedalling.

Thanks to your response I now see the specific cyclic nature of loading
it the key to this.

Many thanks .

--

Martyn Aldis, e-mail [email hidden]
==============================================================================

Martyn Aldis said:

The eccentric on the front bottom bracket of our tandem has been fitted
so that the unit goes in the normal (solo) way round, that is solid
thread to the right. With our cross-over drive this means the drive
side get the plastic ring and the non-drive side the solid thread.

I can see no reason not to reverse the eccentric as the thread
handedness is just inherited from the days when the threads directly
held bearing cups. Is there any reason, internal to the sealed unit
perhaps, why I should not do this and in effect run the unit mainly
backwards?

--

Martyn Aldis, e-mail [email hidden]
==============================================================================

Hi
I have a recumbent in which I have been running a UNBB52 backwards for years with no problems. It originally came with a bottom bracket cartridge on which the cup threaded on to the cartridge and the derailleur mounted on a bracket held in place by the bottom bracket flange. The bottom bracket threads were not needed for this set up, and I discovered only when I went to upgrade it that the threads were backwards. This may have thrown the chainline out, having the long end of the spindle on the wrong side, but with the extra long chain of the recumbent, it was not an issue.
Might want to watch that on a DF bike though.
Dan