On 2 Jul 2006 19:28:17 -0700, "Borrall Wonnell"
wrote:

Blliteration aside,

Are bottom brackets self-centering?

Yes and no. Most do not provide for lateral position adjustment,
which is what I think you're looking for.

I've got a 68mm BB (110mm spindle)
that seems to be off-center on my '02 MTB (with 68mm BB shell). I
think I have installed it correctly...the fixed cup (DS) is screwed in
as far as it can go, such that the flange is pressing against the side
of the BB shell. The free cup is inserted as far as it can go (with a
couple of threads showing). The BB is square taper.

By any chance, was it a Shimano unit that had an unthreaded shoulder
about 2mm wide next to the right flange? There's one design of
UN-series BB that I've encountered which is intended specifically for
use with BB-mounted front ders; using it with a tube-mounted fder will
cause the cranks to be 2mm farther to the left than normal for the
spindle length.

The gap between crankarm and chainstay is larger on the NDS by about
2-5mm. I swapped the crankarms and placed them in various positions on
the spindle to rule them out as a source of the problem...in all cases,
the gap was larger on the non-drive side.

Assuming the frame is symmetrical (it appears to be, and is in good
condition), is this kind of discrepancy acceptable/expected? Have I
installed the BB wrong? Am I doing something else wrong?

I hink the BB that caused this problem for me was a UN52 or UN53; I've
swapped over to the cheaper UN25 (and competitive units) as a result.

I will note, however, that as long as the sprockets don't hit the
chainstay, there's no real problem with having the cranks off center
by an amount this small.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.