Head tube and bottom bracket facing?

dennisn

While I have always thought that facing was a good idea I find myself wondering if it is
really necessary or for that matter actually accomplishes anything useful. I base my thinking on the fact that when you install a bottom bracket(new outboard) it gets screwed in and has no choice but to follow the threads. The instant that any part of it
touches the face of the bottom bracket shell, well, that's as far as it goes, whether it's
touching all around or only in one place. It's only parallel with the other side BB if the threading is parallel not because of any facing that has been done. I guess what I'm saying is that the facing doesn't insure anything. It's the threading that determines how
parallel the bearings are. The head tube and headset(not the new integrated) seem
that they would work on the same principle only not threaded. They races are guided in by the headtube and when any part of them touches the head tube it stops. Whether it's flush all the way around or not. Well, that's it, more or less. Now, am I just plain crazy(easy, easy now) or do I actually make some sense??? :? :?

Dennis Noward

nicklouse

you are assuming that when the cup is fitted it is not distorted during the tightening. also you now have a side load being applied to the unsupported cup.

Not mention the warranty requirements from the bearing supplier.

dennisn

nicklouse wrote:

you are assuming that when the cup is fitted it is not distorted during the tightening. also you now have a side load being applied to the unsupported cup.

Not mention the warranty requirements from the bearing supplier.

You're saying that the inside cup(that touches the shell) has to touch all around or it
is not supported??? As opposed to being self supporting because it's attached to the threads?? Or that the threads alone are not enough to fully support the bearing assembly? The whole bearing assembly must make contact or it will flex?? All this could very well be true but still doesn't insure that both the bearings are parallel because the threading does not continue all the way through the BB shell but starts and stops on each side. Facing only insures that the bearing faces and the shell mate up closely.
I'm starting to get a bad feeling about all this.

Dennis Noward

Smokin Joe

Has anybody suffered premature bearing failure because they haven't had the shell faced? I have never heard of it and all the people I know who have fitted it have not bothered with facing and no one has had a problem. I'm not nescessarely claiming it is not advisable, just wondering what people's real life experiences were.

Barrie_G

I would have thought that the shell would have been faced before the thread was cut anyway.

OK I'm no expert but I've done a little lath work and I was always taught to face off any work I was doing before cutting a thread, as it helps to stop the tap/die from contacting the work piece at a raised point getting knocked off center and cutting the thread at an angle.

dennisn

Barrie_G wrote:

I would have thought that the shell would have been faced before the thread was cut anyway.

OK I'm no expert but I've done a little lath work and I was always taught to face off any work I was doing before cutting a thread, as it helps to stop the tap/die from contacting the work piece at a raised point getting knocked off center and cutting the thread at an angle.

I can understand that and it would seem that the frame maker would do this. Like you
say, to insure getting the tap to cut as parallel to the BB shell as possible. Although, how does the tap aline itself with the shell intially?? Or are all these questions way beyond what the
bearings really need to run smoothly???

Dennis Noward