I ordered a Shimano UN-55 bottom bracket and the left side adapter cup was loose on the bearing housing. Returned that one and ordered a new one, this one is loose also. Are these cups designed to squeeze down on the BB as they are tightened or do I have another defective cup?

Loose when installed or off the bike? They clamp down some as you tighten them into the shell.

What do you mean squeeze "down?

They are supposed to tighten up and hold everything securely in place.

UN55 are cartridge bearing BB type.. you crank down the LH thread right side in, tight.
then the LH side is screwed in. Clockwise, as it is a non corroding plastic structure.,
you don't lean on the wrench so hard..

Not installed the cup ID is about .010 thousands larger than the OD of the bracket housing. This is the aluminum cup model. I have a plastic cup from another bottom bracket and it fits snug around the housing as I would have expected with the aluminum model. I thought that maybe when the cup is installed it would reduce the ID a small amount clamping down on the bracket housing.

Maybe they left room for the inevitable corrosion?

Did you try installing it before returning it as "defective"?

No,I didn't want to install it until I found out if there was a problem. I called Shimano and the man on the phone seemed to think it should fit just like any other bottom bracket. But He didn't sound to sure of himself. He suggested I return it.

Sounds weird. I assume that the 10 mils clearance between LH cup ID and BB sleeve/housing OD reflects the OD of the cartridge bearing itself? If not, and the bearing cartridge is a snug fit into the LH cup, then I think the idea is to torque sufficiently hard to bottom out the cup lip against the frame's BB shell, and this should drive the compression of the cup against the outer edge of cartridge bearing against the BB housing/sleeve to then deform it and that should widen just the end to fill up the gap. If that's not happening and you're already bottoming out that LH cup lip against the frame's BB shell, then I'm thinking you need a wider BB.

Alternately, you might want to try an IRD/Tange Seiki BB that has steel or alloy cup versions, and isn't too heavy. It has a fully recessing LH cup with no lip that works more like the older plastic LH cups BBs from Shimano. So it should be easily snugged tight for most bikes.

I believe you are overthinking this. Install it before deciding there is a problem. There may have been that much play in the last one I installed before I put it in. I didn't really pay attention. Had it been loose AFTER installation, I would have noticed and taken appropriate action.

FWIW the un-55 that I ordered recently had no play in any part prior to installation.

Is the bracket shell size larger on a 73mm bracket than on a 68mm? If so I may have the cup from a 73mm bracket.

Some time I think this place is an OCD support group site

I have a couple of Shimano cartridge BB in the old parts box. One has a tight left side cup and the other is a little loose. I really don't think it's an issue..

I got my 12 yr old son to install a UN55 BB 122.5 mm spindle on a bike this morning. And simply, he did the following, as I instructed him:

a) look at BB shell and make sure threads are clean, surface looks flat and undamaged.
b) take out RH side cup/bearing/spindle and screw it by hand using left hand threaded into BB shell but not all the way.
c) take out LH side aluminum cup and screw it in by hand on the otherside.
d) take torque wrench and tighten RH side first to 35 - 40 ft-lbs torque. Get someone to help hold wrench and frame
e) torque LH side cup 30 - 35 ft-lbs as spec'd.

The first thing to notice is that when RH cup is not tightened, the LH cup may seem a bit loose inside and with some gentle finger grip it's possible to continue to hand-tighten both cups. This is normal. But once the RH side got torqued down tight, even I couldn't tighten the LH cup by hand anymore, even though we had 2 - 3 mm of threads remaining before the cup would bottom out against the bearing.

If you're tightening down the RH side snug, and then doing the LH side and the cup is loose, then it could be the wrong cup, and/or it could be something wring with your BB shell. But if a loose dry fit is showing the LH cup being a bit loose, I wouldn't claim it was a bad part yet until you've torqued it to spec, which is a pretty hefty 400 - 500 inch-lbs of torque (35 - 40 ft lbs.). After achieving that torque, then check if it's still loose.

I'm glad I did a search before I posted this exact problem. I just installed a UN-55 with aluminum cup and it's loose too. I didn't notice when I installed it, but a few days later I started getting an annoying clicking noise from the frame with every hard pedal stroke. It was easy to reproduce by squeezing a crank arm against the seat tube. First I tightened things up and the noise went away for an hour or so. Then I took apart the BB and found the loose cup. I shimmed it with high temp metal chimney tape until snug (two wraps), reinstalled it, and it works just fine now. I didn't measure (I'm not that OCD) but ten mils sounds about right. It looks like a defect to me and I was just going to check here before contacting the vendor. Since I bought it online, it's not easy to return, so I might just leave it as is.

Got a 127 un55, last week, think I'll fit the Plastic left side instead.

The OP had nothing to do with a loose installed BB. The issue was the mounting or left side cuo seemed loose on the cartridge. This does not seem to affect the bb once it's installed, only when you are holding it in your hands. I have never experienced a properly installed Shimano cartridge BB that is loose once torqued properly..

I have only installed a few cartridge BBs, never a UN-55. The cup is loose when held in the hand. Is it supposed to compress somehow under torque? Looking at the frame and the cup, I could not see how that could happen--there is no taper anywhere to do that, at least on my old bike. Maybe newer bikes are different? That's why I added the metal shim, and it fixed my problem, at least for now.

Now that I think about it, I have bought two UN-55's and neither one had any loosely fitting parts. A sample set of two then (at least that's better than one).

+1

1/100000 is not a big deal, remember, the cartridge and the fixed NDS cup need to slide unto eachother blindly and spin independently for installation. I've installed a bunch of these and they've all had a LITTLE room to breathe.

Set it up, then worry about worrying about it.

To answer the question in the OP, IME they're not designed to "squeeze down" on each other, rather the left side is more of a sleeve to stabilize the cartridge.

Interesting. I've purchased three UN55's in the past month. On all three, there was noticeable play between the NDS cup and the NDS end of the BB prior to installation. After installation, all three seemed tight and fine. I really hammered on one last night for a 10 mile sprint and it was not loose when I got home, so perhaps this is not an issue once installed.

I've installed dozens of these over the past several years and never had one that didn't result in a perfect installation. Never noticed the loose cup until recently & did so independently of this thread.

[MENTION=63032]shuff[/MENTION] Did you fit it? was it OK? I have just received mine and it is the same.

The real answer to this non-problem was given in post #2 of this excessive thread. You install the drive side cartridge side first just snug, install the non-drive side cup loosely, tighten the ds cartridge to full torque then tighten the nds cup to full torque if it's metal and just snug if it's plastic. The nds cup will butt firmly against the cartridge and there will be no movement.

Note that the nds cup has no lip to stop it against the bb shell so it will tighten until it firmly seats on the cartridge.

Thanks for the reply. The reason this thread is "excessive" is that it just does not feel right. 1mm between the cup and unit. the The bearing I removed does not have this "non problem", it fits snugly.