Repacking a Shimano BB-UN55 bottom bracket
 

I managed to repack a Shimano BB-UN55 bottom bracket. The process is described in the attachment (pdf). I welcome any feed-back!

https://cimg5.ibsrv.net/gimg/bikefor...23455995e8.jpg

pdf:

https://drive.google.com/file/d/1srj...ew?usp=sharing

The question is, Why would you on a $15 part?

I say why not. Doesn't matter what the replacement cost is it's such a waste to throw away something just because you don't want to spend the time to refresh some grease. Most sealed bearings can be flushed and re-greased just by removing a seal. Takes less time and $$ than driving to the shop to get a replacement or searching on the net for the proper part.

Drill a hole in the BB body and pump grease into it until clean grease comes out.

Just going to throw this out there:

It's shady as hell to attach a file of something (rather than pics) that would be way easier to describe.

Sweet! Always wanted to have a crack at a UN55, you've saved me the swearing!

Even if I never pull one apart myself, it's nice to know how it's put together. Thanks for the write-up!

I find it strange for someone who has a collection of vintage bikes, that you don't consider saving a component instead of replacing it.
For many cyclists, the challenge of rebuilding, repacking, readjusting is half the fun

Well hell I'm impressed. Thanks for the PDF!

Don't get me wrong, I'm all for repairing things that are hard to find, original, or cost/time effective, but I'd say a UN-55 is hardly a vintage expensive unobtanium part.
I just welded up and rebuilt a worn idler pulley bracket on my lawn tractor because it was already apart and I would have had to order the $10 part and wait for it. 15 minutes with the welder and grinder and I was good to go and back together.
I thought the whole point of cartridge BB was to pull them out and replace them as needed.

Always a risk clicking files on the internet. PDFs are usually ok though. The benefit of a document is that it never gets lost.

In what way does cleaning and regreasing (no mention of new balls) accomplish anything when the component has reached "the end of its service life" (from the PDF intro)? There is no mention of inspection of the wear surfaces. On a side note I'm dismayed to find out there are only 7 balls per side in the unit..

It doesn't really seem like a good use of my time to do this, just like repacking hollowtech BBs it doesn't really account for the wear on bearing surfaces so all it does is kick the can down the line a little bit. If I'm gonna spend time removing a BB I want to maximize the time between removals rather than save a few bucks. I go years between square taper BB changes anyway so spreading 20$ over a few years isn't really something that concerns me.

Note, the act of drilling the hole will introduce metal chips inside,
which will at some point, damage the bearings,
although suspended in lots of grease..

Depends, I've repacked Hollowtech BBs because buying them locally involved finding a buyer for one of my kidneys so I could afford them, and I couldn't ride while I waited for mail order ones to arrive. I could see a situation where I didn't want to pay 35 bucks locally for the right length BB, and this keep the can rolling so to speak.
This is an interesting exercise though, It looks like the snap in plastic retainer is what keeps the BB slop free...

Exactly! Amazing how many people will get their knickers in a twist when something tries to expand the knowledge pool a bit. :thumb:

Maybe if you followed the full tear down procedure, and while completely apart , then you could drill that hole ,
clean-out all the metal shavings, then re assemble it,

when you do that , then you would not introduce loose metal bits from just drilling the hole, to mix with the grease, and bugger up the bearings ...

Actually no, PDFs are commonly used to spread malware or viruses.

Tap some thread while at it, to be able to close the hole with a screw, once the re-lubing is finished and prevent any dirt from entering. It could also be used to more easily attach a hose attachment. :)

I use Tape (on black hub, its not apparent,) inside the frame it also would not matter,,
a piece of rubber inner-tube may work fine..

needle grease guns only need a tiny hole..





























..

Really impressive. This guide is really useful since Shimano discontinued BB-UN55 bottom brackets.

You can buy other bottom brackets models, but this is the best one for square taper. The bearings are perfectly aligned into a robutst steel shell, even better than modern bottom brackets.

Regards

On my personal bikes I have yet to have a UN55 BB fail or get to the point of needing a repack. One of the BB's I have has been faithfully serving for at least 20 years and has been on 4 bikes, including one mountain bike where it started its service life.
Only replaced a half dozen of them on customer's bikes in that same time. I like the idea of rebuilding stuff, and now that I see the thing only has 7 balls per side, I am baffled how that BB has been so durable.

Another thread successfully resurrected. Three year old thread.

Yes, it's a good, durable BB. I think one of the reasons is exactly because it has only 7 balls per side. They can be larger than if there were more balls.

https://cimg5.ibsrv.net/gimg/bikefor...6dd38307ea.jpg

The story I got from a few different industry people, back then, is that the Shimano style cartridge BBs were all about speed of factory assembly and having the manufacturer control the bearing preload (as opposed to the shop wrench or rider being able to adjust it, wrongly sometimes). The ease of replacement was the icing on the cake for the LBS service dept. but this benefits the manufacturer or bike factory very little. Andy