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Ode to UN55 BB

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Ode to UN55 BB

Old 10-16-20, 08:18 AM
  #1  
IPassGas
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Ode to UN55 BB

It is sad that Shimano has archived the UN55 BB. I always thought that for its price is was a dependable component and a mostly true "bike standard" (thinking Sheldon on the proliferation of standards). The UN300 is a replacement, but seems unlikely it will be as reliable. Fortunately, there are other manufacturers that are as reliable if at higher cost. So...my Ode to UN55 (posted in one other place)...

The UN55 turns and turns
Nary a click nor a flutter
Runs smooth as butter
Tough as nails and doesn’t cost the farm
With a square spindle that works like a charm
Some say too heavy and must be hollowed
But others revere it as hallowed
Ignored over miles and miles of fun
Rest in peace UN55 knowing a job well done.
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Old 10-16-20, 10:30 AM
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Old 10-16-20, 10:59 AM
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I wish that I had gotten a heads-up on the demise of the UN55, I would have stocked some for future use. It seems like the UN26 is still around, a not-bad second choice. You could keep the metal NDS piece from an old UN55 and replace the plastic UN26 one, it is not a wearing part..
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Old 10-16-20, 11:01 AM
  #4  
John Valuk
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I was thinking recently that, when the original BB on my bike finally gave up the ghost, I'd replace it with a UN55. Just a no-brainer, right?

Then I read about them being discontinued.

So, now I'm waiting on delivery of a UN55 that I don't even need yet.
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Old 10-16-20, 11:02 AM
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I recently ordered and received a couple of UN55s to rehab some of the older bikes in my fleet.

For the low low price,
you can't get a better bearing.
Your seat rails might creak,
but that's just a red herring.

If you need to have
consistent quality
to get your bike
from field to small city,

The UN 55
is your very best bet
to connect your BB shell
to your square taper chain set.
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Old 10-17-20, 08:20 PM
  #6  
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Originally Posted by John Valuk View Post
...Then I read about them being discontinued.
So, now I'm waiting on delivery of a UN55 that I don't even need yet.
I had a similar experience with my BB. I have an Ultegra 3 x 9 drivetrain on my favorite road bike, and read somewhere that the crank interface ("Octalink v1") had been or would be discontinued. I went looking and found an original at a reasonable price... one of only two or three available on that site. I didn't want to have to replace the crankset if the BB wore out. Of course, I may be able to pass the bike on to my son before the original wears out!
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Old 10-17-20, 09:19 PM
  #7  
jsdavis
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IRD QB55 (Made by Tange) about the same price, around $25-30.
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Old 10-17-20, 09:24 PM
  #8  
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Yeah, I had a feeling about the UN55 being discontinued back in summer when REI had 'em on sale for about $8 each. I wondered why any shop would discount anything during a pandemic... then grabbed three in various sizes, including one I can use now, and paid before they changed their minds. I left a few in duplicate sizes, didn't see any need to hoard 'em.

The rest were gone a week later. Still lots of bare spots on the shelves as some shops continue to struggle to keep anything in stock.

Ditto, Shimano 9-speed chains. Didn't need any. At the moment. But for around $8 each, heck, why not.
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Old 10-18-20, 07:34 AM
  #9  
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I see the BB-UN300 is available in size 68 X 122.5 with either a 47.5 chainline or a 50 chainline. I don't think the UN55 was available in two different chainlines. What is the difference between the 47.5 and 50 version of the UN300 and how do I know which is the right one to choose?
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Old 10-18-20, 08:06 AM
  #10  
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Not ironically....my external BB gravel crankset was bugged...and went back to using my IRD Defiant with UN55. Thing is a tank, and about as heavy. Fortunately those things last forever, so it'll have to do
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Old 10-18-20, 08:23 AM
  #11  
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I have a brand new 73mm X 122.5mm UN55 if anybody needs one.
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Old 10-18-20, 10:31 AM
  #12  
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All this negativity and no one yet has given an example of a UN-300 failing more than a UN55.

It seems the UN300 has some engineering to address issues that people have with the UN55 when the threads are not cut perfectly on the same axis between the drive side and non-drive side. Which seems like it might be an issue in several BB threads post here at BF with other cartridge BBs as well as the UN55.
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Old 10-19-20, 08:06 AM
  #13  
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XXCycle still has them at $17 - I picked up an Italian and an English one recently - I like them for use with Stronglight Impact cranks for vintage builds where I want compact rings.
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Old 10-23-20, 12:46 PM
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Originally Posted by Iride01 View Post
It seems the UN300 has some engineering to address issues that people have with the UN55 when the threads are not cut perfectly on the same axis between the drive side and non-drive side. Which seems like it might be an issue in several BB threads post here at BF with other cartridge BBs as well as the UN55.
What's been done to help?

I ran into this issue recently with an eBay Ti BB. For practice, I tried installing it onto an MTB (Jamis frame, should be reliable quality). The old BB was a NECO brand and spun well, but the eBay BB did not when installed, specifically because of the above issue.

So how was it that the NECO worked? There was play in the NDS cup diameter vs bearing that allowed the NDS cup to angle out of alignment, but yet not create any slop with the bearing. That sounds impossible, but that's how it worked.

The eBay BB on the other hand was a tight friction fit between the bearing and cup. So any misalignment caused binding to the bearing.

How are we to be sure when buying BBs that the design accommodates for this? Getting a frame re-tapped is a poor suggestion IMO.
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Old 03-05-21, 07:43 PM
  #15  
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So I just got a UN300 122.5 because a UN55 115 I had laying around wasn't right for the chainline of a build.

The NDS cup doesn't have a lip to provide definitive feedback on when to stop inserting, by clamping up against the frame. Instead it looks like it could screw in endlessly. Is there any better way to know when to stop screwing it in, other than when it stops screwing in?
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Old 03-05-21, 08:09 PM
  #16  
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I suspect there was an oldschool executive at shimano in Japan who has been defending this part and he either just died or retired.
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Old 03-05-21, 09:09 PM
  #17  
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Originally Posted by RubeRad View Post
So I just got a UN300 122.5 because a UN55 115 I had laying around wasn't right for the chainline of a build.

The NDS cup doesn't have a lip to provide definitive feedback on when to stop inserting, by clamping up against the frame. Instead it looks like it could screw in endlessly. Is there any better way to know when to stop screwing it in, other than when it stops screwing in?
A steel shell with that big threaded interface can take a ton of torque. And the cartridge, being designed to withstand craptons of cycles of pedaling forces, is also perfectly happy to be pushed on pretty hard by the cups. So go ahead and torque the crap out of it.

Shimano spec is 50-70nm.

No, that's not a joke. Shimano spec is actually 50-70nm (see page 17).

Anyway, the lack of a flange adds versatility to the BB. For instance, if you put a spacer on the drive side to set the spindle up asymmetrically, there's no flange stopping the NDS cup from inserting far enough to adequately grab onto the cartridge.
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Old 03-06-21, 12:03 AM
  #18  
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Hey that's a good tip, even with the 122.5 I could still use a bit more chainline, I'll try a spacer
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Old 03-06-21, 01:39 AM
  #19  
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Originally Posted by HTupolev View Post

Anyway, the lack of a flange adds versatility to the BB..
Quick UN55 question you might have thoughts on.
So I bought one to put in a 68mm shell, the original axle was 4mm asymetrical, off to the driveside.
I have 4mm of spacers so go on the driveside.
I don't have the 1mm NDS spacer.
I tried it and there's that 1mm gap when it's all tight
Do you reckon it matters at all, not having a spacer under the NDS flange? If many of these don't even have NDS flanges?
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Old 03-07-21, 01:46 AM
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Originally Posted by Soody View Post
I have 4mm of spacers so go on the driveside.
I don't have experience to know if this actually matters, but I've heard claims that using multiple spacers can add enough slop to the BB seating to make it prone to loosening. 4mm BB spacers do exist, so if you're using multiple smaller spacers to achieve a 4mm spacing, it's something to think about... or at least something to remember if you ever do run into an issue with the BB loosening itself and are brainstorming potential solutions.

I tried it and there's that 1mm gap when it's all tight
Do you reckon it matters at all, not having a spacer under the NDS flange?
I wouldn't worry about it. Small gaps on the NDS flange don't seem to be very rare with UN55 bottom brackets. UN55 bottom brackets are pretty common in the wild, so if it was a real issue, I suspect they wouldn't have their reputation as a good fire-and-forget choice.
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Old 05-19-21, 06:39 AM
  #21  
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Originally Posted by RubeRad View Post
So I just got a UN300 122.5 because a UN55 115 I had laying around wasn't right for the chainline of a build.

The NDS cup doesn't have a lip to provide definitive feedback on when to stop inserting, by clamping up against the frame. Instead it looks like it could screw in endlessly. Is there any better way to know when to stop screwing it in, other than when it stops screwing in?
That is because you are supposed to screw the DS cup in first and tighten, then you screw the NDS cup in until it is tight also....simple peeps. Don't forget when removing, to unscrew the NDS cup first to take some of the strain off the DS cup and then unscrew that. It will come off that much easier.
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Old 05-19-21, 09:23 AM
  #22  
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That doesn't help. I did screw the DS in first and tighten, and then screwed the NDS cup in, and without a lip there's no definitive point at which it is 'tight'. But now I'm repeating myself...
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Old 05-19-21, 09:30 AM
  #23  
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Originally Posted by RubeRad View Post
That doesn't help. I did screw the DS in first and tighten, and then screwed the NDS cup in, and without a lip there's no definitive point at which it is 'tight'. But now I'm repeating myself...
Sounds like your BB shell may be too wide for the BB you have. There is an internal edge to the NDS cup that should abut the BB cartridge assembly. This exists whether or not the NDS cup has an external edge/flange. If you look at those square taper BBs with the external flange on the NDS cup, the cup will usually come up to torque before the flange contacts the BB shell.
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Old 05-20-21, 06:42 PM
  #24  
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Originally Posted by jsdavis View Post
IRD QB55 (Made by Tange) about the same price, around $25-30.
Given the fact that Tange made the UN55, (along with every other Shimano bottom bracket I know of,) I'd not be surprised to learn that the QB55 is the exact same part.

--Shannon
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Old 05-20-21, 07:03 PM
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Without a UN55 you’re up a creak without a pedal?
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