Need Help Installing UN-73 BB

[Eric]

Anybody have advice on installing a UN-73 BB?

I can thread in either side alone by hand, but when I thread in both the plastic cup (Left side)and
the drive side it seems that the last 1-2mm don't want to go. When I try and torque the drive side I
can tell that I am pushing against plastic rather than tightening into the threads.

This is on an RB-1, and the size is 68x115.

My BB did not come with any instructions, is this typical? Other Shimano products I have bought
included good instructions. Purchased from Performance.

Thanks. Eric Peterson

 

[Dave Thompson]

"Eric" <[email protected]> wrote in message news:[email protected]...
> Anybody have advice on installing a UN-73 BB?
>
> I can thread in either side alone by hand, but when I thread in both the plastic cup (Left
> side)and the drive side it seems that the last 1-2mm don't want to go. When I try and torque the
> drive side I can tell that I am pushing against plastic rather than tightening into the threads.
>
> This is on an RB-1, and the size is 68x115.
>
> My BB did not come with any instructions, is this typical? Other Shimano products I have bought
> included good instructions. Purchased from Performance.
>
> Thanks. Eric Peterson

Make sure that your BB threads are well greased. Install the drive side till snug, then install the
left side until snug. Torque the driveside to 25~35 ft lbs and then tighten the left side. Don't
torque the left side, it just needs to be tight. The UN-72/73 doesn't come with instructions.

 

[Qui Si Parla Ca]

adkerp-<< Anybody have advice on installing a UN-73 BB?

I can thread in either side alone by hand, but when I thread in both the plastic cup (Left side)and
the drive side it seems that the last 1-2mm don't want to go. When I try and torque the drive side I
can tell that I am pushing against plastic rather than tightening into the threads.

This is on an RB-1, and the size is 68x115.

My BB did not come with any instructions, is this typical? Other Shimano products I have bought
included good instructions. Purchased from Performance. >><BR><BR>

I rec. taking the frameset to a decent LBS and have them chase the BB threads, making sure they are
deep enough.. Also tap the right cup off, use some grasso in there, and replace. This will prevent
creaking in the future.

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

 

[Robin Hubert]

"Qui si parla Campagnolo" <[email protected]> wrote in message
news:[email protected]...
> adkerp-<< Anybody have advice on installing a UN-73 BB?
>
> I can thread in either side alone by hand, but when I thread in both the plastic cup (Left
> side)and the drive side it seems that the last 1-2mm don't want to go. When I try and torque the
> drive side I can tell that I am pushing against plastic rather than tightening into the threads.
>
> This is on an RB-1, and the size is 68x115.
>
> My BB did not come with any instructions, is this typical? Other Shimano products I have bought
> included good instructions. Purchased from Performance. >><BR><BR>
>
>
> I rec. taking the frameset to a decent LBS and have them chase the BB
threads,
> making sure they are deep enough.. Also tap the right cup off, use some grasso in there, and
> replace. This
will
> prevent creaking in the future.
>

Peter, Have you had the good luck to be able to examine an UN-73? It's basically an UN-52 with a
hollow spindle.

--
Robin Hubert <[email protected]

 

[Paul Kopit]

On Thu, 14 Aug 2003 21:56:22 -0700, "Dave Thompson" <[email protected]> wrote:

>Make sure that your BB threads are well greased. Install the drive side till snug, then install the
>left side until snug. Torque the driveside to 25~35 ft lbs and then tighten the left side. Don't
>torque the left side, it just needs to be tight. The UN-72/73 doesn't come with instructions.

I don't think you are correct. You install the drive side snugly. It has the bb body attached to it.
You torque the non drive side. At least that is what Barnett's manual says.
<http://rideitbent.net/pdf/barnetts_ch10.pdf

 

[Dave Thompson]

"Paul Kopit" <[email protected]> wrote in message
news:[email protected]...
> On Thu, 14 Aug 2003 21:56:22 -0700, "Dave Thompson" <[email protected]> wrote:
>
> >Make sure that your BB threads are well greased. Install the drive side
till
> >snug, then install the left side until snug. Torque the driveside to
25~35
> >ft lbs and then tighten the left side. Don't torque the left side, it
just
> >needs to be tight. The UN-72/73 doesn't come with instructions.
>
> I don't think you are correct. You install the drive side snugly. It has the bb body attached to
> it. You torque the non drive side. At least that is what Barnett's manual says.
> <http://rideitbent.net/pdf/barnetts_ch10.pdf>
>
You can't torque the non-drive side, it's plastic or composite. It seems to be used as a guide and
support for the spindle.

 

[Paul Kopit]

On Fri, 15 Aug 2003 11:07:32 -0700, "Dave Thompson" <[email protected]> wrote:

>You can't torque the non-drive side, it's plastic or composite. It seems to be used as a guide and
>support for the spindle.

The drive side of the bb has a lip and you aren't torquing the unit. The non drive side, plasit, can
move into the bb. Sad to say, you torque the plastic.

 

[Mikeyankee]

>the last 1-2mm don't want to go.

I've been puzzled by this too, as earlier Shimano BB's (UN-72) worked fine.

Though I ain't no pro, here's what I've have done on two of my bikes. My rain/beater bike has ~ 1000
hilly miles on the UN-73 without the slightest noise or problem.

Clean & grease threads and inside surfaces of cups. Tighten the drive side, then install the NDS
plstic cup as far as it will go with normal torque. Let it protrude a couple of mm if it wants to;
doesn't seem to hurt anything. The shoulder of the cup SEEMS to be in proper supportive contact with
the BB cartridge.

I'm getting a couple of extra UN-73's for spares and intend to measure their NDS cup against those
of older UN-72's, to see if they're deeper or anything. If so, it may be prudent to shave off the
inside 2 mm or so of the plastic cup before installing.

Mike Yankee

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

 

[Dan Daniel]

On Sat, 16 Aug 2003 10:04:05 -0700, "Dave Thompson" <[email protected]> wrote:

>
>"Dan Daniel" <[email protected]> wrote in message
>news:[email protected]...
>> On 16 Aug 2003 02:09:08 GMT, [email protected] (ADKERP) wrote>
>>
>> From the Park site about bottom bracket installation (scroll down)
>> http://www.parktool.com/repair_help/FAQcartdg.shtml
>>
>> "Use BBT-2 [Park's model number] to snug fixed flange against face of bottom bracket.
>>
>> "Thread in removable ring to appropriate side.
>>
>> "Secure removable ring to at least 360 inch pounds using torque wrench. If you are using hand
>> wrench, and are holding the wrench 6 inches from axle, apply 60 pounds of pressure. which is
>> tight. By securing removable ring, you are securing the other side at the same time. Removable
>> ring pushes against fixed flange."
>>
>>
>> With the UN-72/3, the right/drive side cup is the fixed one- screw it in until it bottoms out
>> against the face of the bottom bracket. Then the left side ring goes on and is tightened.
>>
>The only problem with that, is with the UN-72/73 the removable ring (left side) being made of
>plastic, it will let go (strip out) much sooner than when the 360 inch-pounds (30 foot-pounds) of
>torque is reached. And if you only "snug" the drive-side down 'till it bottoms out on the face of
>the bottom bracket shell, then you will soon have a loose/creaky bottom bracket. The solution, at
>least in this case, it to install the bottom bracket drive side and snug when it bottoms on the
>shell, install the removable ring (non-drive side) and snug it down tightly, then torque the
>drive-side to the torque specs. That's what I did and it works perfectly well for me.
>

I don't have a torque wrench, so I don't know what I finally end up with. All I can say is that I
have gone 'very tight' with the left side cups on UN-72s and UN-52s. I believe that at least one of
the UN-52s had a plastic cup.

From Shimano's web site:

http://bike.shimano.com/product_images/BB/si_images/BB_UN40_SI.pdf

they say to install the drive side and then tighten the left side (adapter) to 435 in. lbs minimum
(zoom in on the 'Installation of Front Derailleur' section for instructions on installing the
bottom bracket). This is for a UN-40, which is probably a pretty cheap model, and probably has a
plastic cup.

I don't understand how you can run the drive side down until it hits the bottom bracket wall, and
then tighten it much further in a way that would be putting enough pressure on the left side adapter
to stress the threads enough to not be prone to loosening. But however the physics work, you have
had success with it, so it's obviously an effective way to do it.

 

[Paul Kopit]

On Sat, 16 Aug 2003 10:04:05 -0700, "Dave Thompson" <[email protected]> wrote:

> then torque the drive-side to the torque specs. That's what I did and it works perfectly
> well for me.

Your way, the part you are torquing rotates it's lip against the frame and can easilly damage it.