Bottom bracket square taper cartridges

[Ajax Bay]

I think @GuyBoden knows more about this: see his 2021 thread and I've clipped this UN-55 internal view.
https://www.cyclechat.net/threads/w...he-discontinued-shimano-bb-un55.274954/page-5
And maybe @rogerzilla

looks like roller bearing on (I think) the drive side. Not sure about the different sized balls. The races (on the right above) seem different widths. And see my post: https://www.cyclechat.net/threads/w...ed-shimano-bb-un55.274954/page-7#post-7047239

 

[I like Skol]

I think @GuyBoden knows more about this: see his 2021 thread and I've clipped this UN-55 internal view.
https://www.cyclechat.net/threads/w...he-discontinued-shimano-bb-un55.274954/page-5
And maybe @rogerzilla
View attachment 725695
looks like roller bearing on (I think) the drive side. Not sure about the different sized balls. The races (on the right above) seem different widths. And see my post: https://www.cyclechat.net/threads/w...ed-shimano-bb-un55.274954/page-7#post-7047239

Looks like @faster was pretty close to the mark then? Definitely not serviceable.

I was going to suggest if anyone had an old UN54/55 they wanted to post to me I would run a cutting disc through it to find out what it contains, but you saved me the job. I'm impressed that it contains roller bearings, that's pretty neat. What this cross section does show is that there is nothing magic in the fabled Shimano BBs. They simply got it right with quality materials, good tolerances, the right grease and some kick-ass seals that kept out the crud. It's not rocket science, which is why I don't understand how they screwed it up so badly with the later BB formats that just don't come close to the square taper life expectancy?

 

[I like Skol]

Unless of course, they wanted to sell more BBs ££££££