dedhed

The drive side must always be installed tight to the shell as this is what holds it. The NDS cup just supports and centers that side. I have one where the NDS doesn't go all the way in but enough to clear the crank arm

I typically start the DS then loosely install the NDS to keep things centered, then tighten the DS, finally finish off he NDS

Papa Tom

In the final installment of my BB melodrama, I was able to thread the drive side all the way into the BB shell. However, once this was all the way in, i could not thread the non-drive side all the way in. It was sort of a trade-off, and the photo you saw was of BOTH sides backed-off a little. At that point, I hadn't realized that threading the non-drive side in had pushed the drive side OUT a few threads.

So, right now, I've got the drive side flush (bedded?) against the shell, but the non-drive side is backed off about two threads. You may have noticed in the photo of the two BB's that the insert for the non-drive side (new BB) is a little longer than the one for the old BB. I tried using the old non-drive piece with the new drive-side piece and it did not work.

It's Thursday, so it should only be a couple of days before I have my answer regarding the newer new BB. The UN55 that I am currently struggling with turns out to be a 73mm X 122, and you can see that the axle is longer than my old one, which must have been a 113.

trailangel

3 pages and you haven't measured the shell?
Surely there is a ruler in your home.

dedhed

Inches work fine X 25.4

Iride01 

That spindle length of 122 vs the old 113 would have been another issue if all 9 mm of the difference was on the drive side even if you did get it to fit the BB shell securely.

Papa Tom

My eyes are not good enough anymore (even with readers on) to see the difference between 68mm and 73mm. It looks closer to 68mm.

Yes, three pages is a lot of discussion about this. I truly appreciate all the input, but once people start asking questions that have already been answered, making suggestions that have already been tried, and accusing me of not having a ruler, it's time to put it to bed! I will let you all know how the 68mm X 113 works out.

Thanks again!

tomtomtom123

Well, it's like wearing a shirt from some brand somewhere, walking into a clothing store in Mongolia, and telling the clerk to sell you another shirt that will fit based on the name of the brand of the shirt that you are wearing, without taking any measurements.

Papa Tom

Guys, I'm done with this. Thank you for your help and your unsolicited critiques of my character.

bldegle2

GO TO HARBOR FREIGHT....

There are a lot more uses for the calipers than this project. Go buy one, it would be the best $10 you spent on this project so far.

Plus, you would have answers by now, and a bike that you could ride...

delbiker1 

Ditto on this post.

LV2TNDM

Actually, although this is technically true, it is effectively false. A 2.5mm spacer on the DS will space the cranks too far to the right. Spindle length is a function of proper chain line and chain stay clearance. Spacing it out throws this off. So the result would be shifted too far right. Not much, but it makes a difference and the left crank arm may be too close to the left chain stay. Either way, the cranks would no longer be symmetrical in the frame.

And no, a 122.5 length spindle is NOT what you want to use with a crankset requiring a 113. That's basically 10mm too long, which is just to much.

Russ Roth

It's not false at all, spindle length is spindle length regardless of the frame, so if you have the right spindle length in a 73mm bb which is 5mm too wide, a 2.5mm spacer on each side will leave the spindle centered to the frame just as it should be; too long a spindle is a different issue but I specifically stated as long as the spindle length is right. So a 73x113 bb with 2 spacers, one to each side, will work every bit as well as a 68x113, nothing effectively false about it as the 113 spindle will leave the crank in the same exact position.

LV2TNDM

Ha, you're right! But the spacers do matter, but more specifically, their absence matters most. In this case, without the spacer, the spindle would protrude too little from the right side, placing the rings and crank arm too close to the right chain stay. I had it backwards. Yes, centering the BB within the shell determines proper crank placement, and using a 2.5mm spacer does this. No spacer needed on the NDS because the cup doesn't contact the outer face of the BB shell. Perhaps utilize a traditional adjustable cup lockring to hold it in place for extra security, given the reduced thread engagement.

dedhed

Many of the Shimano cartridges have no real "lip" on the NDS cup so a spacer cannot be used. The NDS cup only has to go as far as needed to center & support the NDS of the cartridge.

Like this UN 54 on my hybrid and most UN 26.

If you look at the photo of the OP's original UN 72 BB the NDS cup has no lip.

Russ Roth

BB spacers barely fit over the threads, so that barely there lip is all that is needed, admittedly, not all BB cups have a lip but as LV2TNDM points out, with this style of bb the left side spacer can be a redundancy, the cup really serves a wedge function and can do that sans spacer, though from an aesthetic stand point I like the spacer there if the cup has a lip like your BB does, just makes it look more like someone knew what they were doing.

Papa Tom

The 68 X 113 UN55 bottom bracket fits like a glove. So, either the Bicycle Blue Book is wrong about the 1996 GT Outpost using a 73mm, or my bike is not a 1996, after all. I BOUGHT it that year, but maybe it's 1995 or earlier? I noticed that the Blue Book doesn't list a BB for the '95, so who knows.

Anyway, this chapter is closed. Thanks for all your help.

If anybody needs a brand new UN55 173 X 122, let me know. It has been installed and immediately removed, so it's a little dirty and the box is slightly torn, but it will work like new.

dedhed

Measure twice & buy once?

Papa Tom

You must have missed my earlier posts in this thread. There was NEVER a measurement. This was the third or fourth time I've replaced this BB and, each time, store owners sold me the correct one. Truthfully, I never knew there were so many variations on a single BB skew. I just figured a UN72 is a UN72 is a UN72 and a UN55 is a UN55 is a UN55. The last one I bought was through a fairly reputable online source and they messed up - although, to be fair, they probably referred to the Bicycle Blue Book, which lists the 1996 GT Outpost as using a 73mm BB.

Anyway, it's done now and I can move on to the business of not riding because of COVID-19. Ironically, this time, I blindly ordered TWO of these BB's, so the REAL heading of your post should have been "Measure no times and buy twice!"