Re: BB question

"geepeetee" <geepeetee@xxxxxxxxx> wrote:

I have just bought a Shimano sealed BB off eBay but when it arrived it
doesn't fit my bike. My fault but I am after info about threads commonly
used.

The shell I want to put it in is from a kids mtb, it was the donor bike
for a recumbent I have recently finished. It has the cup and bearing
type of arrangement with a lock ring for adjustment. I have compared
several of these on random bikes and were the same thread so it
must be a pretty standard type.

I just want to make sure I buy the right one next time, are there any
identification markings on shimano BB that tell the size and type?

There are only two common threaded BB standards in current production,
Italian and British, the latter being by far the more common. A British
thread is 1.37" x 24tpi with a left-hand-threaded right cup, while Italian
is 36mm x 24tpi with both cups right hand threaded.

Look for markings on the cups. A British unit will sometimes be marked ENG,
BSC, BC, ISO, or similar, while an Italian may be marked IT, ITA, etc.

The UN72 I have in my hand says BC1.37 on the flanged (right hand) cup.

An Italian unit is too big to fit in a British shell. A British unit will
slip into an Italan shell without any thread engagement, and it will
rattle.

I suspect you're either trying to put an Italian unit into a British shell,
or you may just be trying to insert a British unit the wrong way round.

James Thomson


.

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