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I've just tried (and failed) to upgrade from a cup and cone bottom
bracket to the ubiquitous Shimano BB-UN54 cartridge bottom bracket.
In rec.bicycles.tech I've seen mention of ensuring that the faces of
the BB shell are true and I'm wondering if this could be part of my
problem.
It's a 68mm shell (I measured it at 68.09mm) and a 68mm cartridge but
they wouldn't go. I screwed the plastic cup in hand tight then began
tightening the BB itself from the drive side but it wouldn't go the
last 1-1.5mm. I removed everything and checked it over (measured
roughly, the distance from the inner face of the drive side to the
inner face of the plastic side came out more like 70mm than 68mm but
it was only a rough measurement and I assumed some crushability in the
plastic), the BB shell threads were clean, so I guessed this was how
it was meant to be. The second attempt caused the plastic cup to pop
out under the load, so something definitely isn't right, the cartridge
literally pushed it out the other side. As you'd expect the threads
on the plastic cup are pretty well rooted now, though probably still
serviceable since if my assumption is right it primarily supports the
BB within the shell.
I removed everything again then screwed the plastic cup back in and
noticed that there's a gap big enough to get my fingernail in at the
top when it's fully seated (and then some) at the bottom. I don't
know if was the case before I popped it or not, but I take this to
mean that the faces of the BB shell aren't true, though it could be
the plastic is stuffed.
So I guess I need to know; should I get the BB shell faced, is this
something the one and only LBS should be able to do (rough price
guide?) or will I just machine a bit off the inside of the plastic cup
so that the cartridge no longer drives it out and cut my losses? I'm
guessing I can't get a new plastic cup, so I won't even ask. I'm a
bit bemused, I bought a cheap VP components BB ages ago off eBay and
it went straight into one of my other bikes without even a hint of
trouble and it had a metal non drive side cup too (a plus in my "steel
is real" book), yet the Shimano...
bracket to the ubiquitous Shimano BB-UN54 cartridge bottom bracket.
In rec.bicycles.tech I've seen mention of ensuring that the faces of
the BB shell are true and I'm wondering if this could be part of my
problem.
It's a 68mm shell (I measured it at 68.09mm) and a 68mm cartridge but
they wouldn't go. I screwed the plastic cup in hand tight then began
tightening the BB itself from the drive side but it wouldn't go the
last 1-1.5mm. I removed everything and checked it over (measured
roughly, the distance from the inner face of the drive side to the
inner face of the plastic side came out more like 70mm than 68mm but
it was only a rough measurement and I assumed some crushability in the
plastic), the BB shell threads were clean, so I guessed this was how
it was meant to be. The second attempt caused the plastic cup to pop
out under the load, so something definitely isn't right, the cartridge
literally pushed it out the other side. As you'd expect the threads
on the plastic cup are pretty well rooted now, though probably still
serviceable since if my assumption is right it primarily supports the
BB within the shell.
I removed everything again then screwed the plastic cup back in and
noticed that there's a gap big enough to get my fingernail in at the
top when it's fully seated (and then some) at the bottom. I don't
know if was the case before I popped it or not, but I take this to
mean that the faces of the BB shell aren't true, though it could be
the plastic is stuffed.
So I guess I need to know; should I get the BB shell faced, is this
something the one and only LBS should be able to do (rough price
guide?) or will I just machine a bit off the inside of the plastic cup
so that the cartridge no longer drives it out and cut my losses? I'm
guessing I can't get a new plastic cup, so I won't even ask. I'm a
bit bemused, I bought a cheap VP components BB ages ago off eBay and
it went straight into one of my other bikes without even a hint of
trouble and it had a metal non drive side cup too (a plus in my "steel
is real" book), yet the Shimano...