Overdue update: I swapped out the old Shimano UN40 BB (68x113) for a new
UN54 68x107 today. I gained a steel leftside cup, and a much better
chainline on the Quickbeam. Back in early November, when I found the old
cracked cup, I just put in a new plastic cup. It promptly cracked upon
install, but
Adding another voice to the ride it cracked crowd. I've installed,
ridden, and otherwise abused BBs with a crack all of the way across the
threads, and they worked fine for as long as the BB lasted. Moreover, I
once ground most of the threads off the drive side of a cartridge BB
because the
Steel cup'd Tange bottom brackets are available here, if you decide to go
that route. I've used them--they're good.
http://www.benscycle.net/index.php?main_page=advanced_search_resultsearch_in_description=0keyword=tange+bottom+bracket
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Some Shimano BBs have a plastic cup. They actually work just fine for many
miles, but stomping on a loose one will crack it. You either need a
nice/new/affordable no-plastic replacement from Rivendell, or this is your
excuse to buy a fancy schmantzy Phil. Because you can adjust chainline.
Yes, you likely have a UN54 BB in there ... and it has a plastic cup. The
reason they usually break is people overtighten them. The need not be
torqued as the misguided instructions say! Just snug is fine. But hey,
plastic is just a bad idea period, for anything in the BB.. and Shimano's
use
I am working over the new 66cm Quickbeam, and saw the cranks were flopping,
which turned out to be from a loose BB. It's a sealed cartridge Shimano
unit, had been installed by Riv. I guess the rings came loose, and the
previous owner hadn't noticed.
BUT... the left side ring is plastic, is that
