UN73

[Steve]

I installed a Shimano UN91 b-bracket on a Ti Lemond a year ago and have just
replaced it (pitting/creaking, etc...) with a UN73. It's what the shop had.

The UN91 was a "thread in from the left" which was no big deal. My 2 other
road bikes use UN72's, so I'm familar with the installations.

The UN73 has a much wider (greater threads) left cup, that will not screw
in/set in to the bottom bracket shell as far as the UN91, nor will it set in
as far as the UN72's on my other 2 bikes. It has about 10mm or so of thread
on the outside of the shell, where as the UN72's were flush to the shell.

The 73 is seemingly is a tight as it needs to be - I've used torque
wrenches, setting to the pressure as recommended on the Park Tool site.

My question is, is having this much thread exposed normal ?. The 73 does
use a cup that has a good bit more threads then the UN72's I'm familiar
with.

FWIW, the crank arms are equal distance from the chainstays (or at least
within a few mm of each other) so all looks kosher and the cranks feels
solid with no play.

Won't ride until I'm sure.

Thanks in advance.

Steve B.

 

[MikeYankee]

I have UN-73's on two of my six bikes right now and have also noticed that the
left cup doesn't screw in fully. But they've worked fine for several thousand
miles with nothing loosening or making noise. So I'd say it's nothing to worry
about.


Mike Yankee

(Address is munged to thwart spammers.
To reply, delete everything after "com".)

 

[Sheldon Brown]

Steve wrote:
> I installed a Shimano UN91 b-bracket on a Ti Lemond a year ago and have just
> replaced it (pitting/creaking, etc...) with a UN73. It's what the shop had.
>
> The UN91 was a "thread in from the left" which was no big deal. My 2 other
> road bikes use UN72's, so I'm familar with the installations.
>
> The UN73 has a much wider (greater threads) left cup, that will not screw
> in/set in to the bottom bracket shell as far as the UN91, nor will it set in
> as far as the UN72's on my other 2 bikes. It has about 10mm or so of thread
> on the outside of the shell, where as the UN72's were flush to the shell.
>
> The 73 is seemingly is a tight as it needs to be - I've used torque
> wrenches, setting to the pressure as recommended on the Park Tool site.
>
> My question is, is having this much thread exposed normal ?. The 73 does
> use a cup that has a good bit more threads then the UN72's I'm familiar
> with.
>
> FWIW, the crank arms are equal distance from the chainstays (or at least
> within a few mm of each other) so all looks kosher and the cranks feels
> solid with no play.

I wonder if you might have accidentally gotten a BB intended for an over
sized (73 mm) bottom bracket shell, rather than the much more common 68
mm size.

It's normal for a few threads to be visible on the left side, but if
there are a lot, it might be worth re-checking.

It was a bit boneheaded of Shimano to designate the model "UN-73" when
"73" is also one of the dimensions.

Reminds me of the scale-focussing Olympus camera that had distance
markings of 2.8, 4, 5.6, 8, 11 and infinity, all too easily confused
with the f-stop control. (Going from memory here, might not have been
all of those numbers...)

Sheldon "Oops!" Brown
+----------------------------------------------------+
| The two most common elements in the Universe are |
| hydrogen and stupidity. --Harlan Ellison |
+----------------------------------------------------+
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

 

[ZeeExSixAre]

> Reminds me of the scale-focussing Olympus camera that had distance
> markings of 2.8, 4, 5.6, 8, 11 and infinity, all too easily confused
> with the f-stop control. (Going from memory here, might not have been
> all of those numbers...)

Hehe, that probably wouldn't be coincidence if they had all 5 of those...
maybe they intended it as an easter egg

--
Phil, Squid-in-Training

 

[Qui si parla Campagnolo]

sbm-<< The UN73 has a much wider (greater threads) left cup, that will not
screw
in/set in to the bottom bracket shell as far as the UN91, >><BR><BR>

They sold ya a BB for a 73mm shell, not a 68mm shell..

Peter Chisholm
Vecchio's Bicicletteria
1833 Pearl St.
Boulder, CO, 80302
(303)440-3535
http://www.vecchios.com
"Ruote convenzionali costruite eccezionalmente bene"

 

[Steve]

"Qui si parla Campagnolo " <[email protected]> wrote in message

m15.aol.com...
> sbm-<< The UN73 has a much wider (greater threads) left cup, that will not
> screw
> in/set in to the bottom bracket shell as far as the UN91, >><BR><BR>
>
> They sold ya a BB for a 73mm shell, not a 68mm shell..
>
> Peter Chisholm

Yep, they sure did (LBS).

Question is, does it matter, except for appearences.

My guess would be that it'll work just fine

SB

 

[Dan Daniel]

On Wed, 28 Apr 2004 16:14:22 GMT, "Steve" <[email protected]>
wrote:

>
>"Qui si parla Campagnolo " <[email protected]> wrote in message
>
>m15.aol.com...
>> sbm-<< The UN73 has a much wider (greater threads) left cup, that will not
>> screw
>> in/set in to the bottom bracket shell as far as the UN91, >><BR><BR>
>>
>> They sold ya a BB for a 73mm shell, not a 68mm shell..
>>
>> Peter Chisholm
>
>Yep, they sure did (LBS).
>
>Question is, does it matter, except for appearences.
>
>My guess would be that it'll work just fine
>
>SB
>

When I installed a 68 width in a 73 BB shell, the cranks were offset
to the right. Along with the left cup going in a bit far, this is
what made me realize what I had done.

Technically it would matter, Your cranks will be offset 2.5 mm to the
left. The right cup will stop on the face of a 68 mm shell, but it is
designed to be 2.5 mm further out.

As to whether a chainline 2.5 mm off is bothersome to you....

 

[Steve]

"Dan Daniel" <[email protected]> wrote in message

> When I installed a 68 width in a 73 BB shell, the cranks were offset
> to the right. Along with the left cup going in a bit far, this is
> what made me realize what I had done.
>
> Technically it would matter, Your cranks will be offset 2.5 mm to the
> left. The right cup will stop on the face of a 68 mm shell, but it is
> designed to be 2.5 mm further out.
>
> As to whether a chainline 2.5 mm off is bothersome to you....

The spindle length is the same, 68 or 73 (or so I believe) and the crank
arms are almost equal distance from the chainstays. The left cup just
sticks out further.

Everything about the b-bracket seems identical to a spare UN72/115/68 I have
in a drawer (except the spindle length, of course), just the left side cup
is longer.

Being that the box says "68" and had no crank bolts, I suspect this is an
older bracket (NOS) that was sitting in the drawer at the LBS and possibly
has been returned on a prior occasion, with some mix and (no) matching
having occurred.

Whatever, it's being removed and returned tomorrow.

SB