Ode to UN55 BB
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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.
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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Oddball: [groans] Don't hit me with them negative waves so early in the morning. Think the bridge will be there and it will be there. It's a mother, beautiful bridge, and it's gonna be there. Ok?
Oddball: [Later: Oddball is looking through binoculars at the bridge] Still up!
Oddball: [planes fly and bomb the bridge] ... No it ain't. See what sending out them negative waves did, Moriarty?
Moriarty: That ain't my fault, Oddball, I've done nothing but have good thoughts about that damn bridge ever since we left!
Oddball: [Later: Oddball is looking through binoculars at the bridge] Still up!
Oddball: [planes fly and bomb the bridge] ... No it ain't. See what sending out them negative waves did, Moriarty?
Moriarty: That ain't my fault, Oddball, I've done nothing but have good thoughts about that damn bridge ever since we left!
Spoiler
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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..
#4
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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.
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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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.
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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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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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.
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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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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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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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.
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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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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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.
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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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?
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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I suspect there was an oldschool executive at shimano in Japan who has been defending this part and he either just died or retired.
#17
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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?
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?
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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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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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?
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?
#20
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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 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.
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?
Do you reckon it matters at all, not having a spacer under the NDS flange?
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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?
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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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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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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Without a UN55 you’re up a creak without a pedal?
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