Bottom Bracket Facing Required?

rust in the bearings has /nothing/ to do with facing of the bb. that's a
moisture ingress problem.


Patrick W. wrote:

See, I figure not facing would allow more water to ingress around the
shell face. I've always had the idea that paint, no matter how smooth and
even it appears, is not perfectly smooth and would allow some seepage.
Facing OTOH would completely flatten and smooth everything.

I replied:

Facing is not about removing paint, it's about removing metal. If a frame
has been properly faced once, it never needs to be faced again.

After a repaint, excessive paint can be removed from the faced surface
with a knife or a fine file, used gently.

This is not intended to be a hermetically sealed interface.

With most modern cartridge bottom brackets, facing is not needed, and
leaving the paint in place can help prevent rust.

Patrick W. wrote:

This was not a cartridge BB. That's my point!!!

I understand that, but I also understand that your frame had already
been faced once, so it doesn't need to have it done again.

The comment about cartridge bottom brackets was not referring to your
specific bike, since it has already been faced, but was a more general
comment directed to other readers of this thread.

Presumably you to will upgrade to a cartridge unit since your old cup
and cone unit is apparently toasted.

Sheldon "Facing Reality" Brown
+---------------------------------------------+
| I have suffered from being misunderstood |
| but I would have suffered a hell of a lot |
| more if I had been understood. |
| --Clarence Darrow |
+---------------------------------------------+
Harris Cyclery, West Newton, Massachusetts
Phone 617-244-9772 FAX 617-244-1041
http://harriscyclery.com
Hard-to-find parts shipped Worldwide
http://captainbike.com http://sheldonbrown.com

push it
with them (nor will I have them service in the future, however).
rust in the bearings has /nothing/ to do with facing of the bb. that's a
moisture ingress problem.

Patrick W. wrote:
See, I figure not facing would allow more water to ingress around the shell
face. I've always had the idea that paint, no matter how smooth and even it
appears, is not perfectly smooth and would allow some seepage. Facing OTOH
would completely flatten and smooth everything.

Sure but is it critical? Maybe but not likely. There are so
many variables here it's not reasonable to concentrate on
the facing of a BB that was most probably flat before paint.

Paint isn't normally an issue on a squared BB - unless
there's a drip or sag.

Was the BB lubed properly? Was it set up just a touch too
loose or tight? Was the environment the same for your 12
year span as for the 1.5 year? A change of
neighborhood/route changes salt water spray for example.

--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

On Thu, 20 Jan 2005 16:30:48 GMT, "Patrick W."
may have said:

push it
with them (nor will I have them service in the future, however).

rust in the bearings has /nothing/ to do with facing of the bb. that's a
moisture ingress problem.


See, I figure not facing would allow more water to ingress around the shell
face. I've always had the idea that paint, no matter how smooth and even it
appears, is not perfectly smooth and would allow some seepage. Facing OTOH
would completely flatten and smooth everything.

Leaving a surface that's open to corrosion from the edges.

If the bearings aren't sealed, then water's going to get in via the
spindle anyway, and possibly down the seat tube as well. If they are
sealed, then it's more important to make sure water can get out so
that it doesn't cause the BB to corrode in place, which is why some
manufacturers routinely drill a hole in the bottom of the BB shell to
provide a drain. Facing the shell isn't done for water exclusion,
it's done for bearing and mounting part alignment. With a sealed BB
whose shoulder is on the right, only the right side of the BB shell
would get faced.



--
My email address is antispammed; pull WEEDS if replying via e-mail.
Typoes are not a bug, they're a feature.
Words processed in a facility that contains nuts.

On Thu, 20 Jan 2005 13:42:52 -0500, Sheldon Brown
may have said:

Patrick W. wrote:

This was not a cartridge BB. That's my point!!!

It was also about 10 years old, and by your description had been
ridden quite a lot. If there were shaft seals on the unit, they were
probably near failure before the work was done anyway, and they aren't
something that gets replaced without putting in a new BB. The water
you observed is far more likely to either have come in along the
spindle (or even down the seat post, for that matter) than past the
threads.

I understand that, but I also understand that your frame had already
been faced once, so it doesn't need to have it done again.

The comment about cartridge bottom brackets was not referring to your
specific bike, since it has already been faced, but was a more general
comment directed to other readers of this thread.

Presumably you to will upgrade to a cartridge unit since your old cup
and cone unit is apparently toasted.

After which the problem ought to be solved.

--
My email address is antispammed; pull WEEDS if replying via e-mail.
Typoes are not a bug, they're a feature.
Words processed in a facility that contains nuts.