Facing BB Shell: Necessary or Recommended?
 

Hi all,

I upgraded my front crank from Ultegra 50/39 with traditional cartridge bearings to newer Ultegra compact with outboard bearings. I did not have the BB shell faced, but now I'm wondering, should I have? Is this an absolute necessity, or just recommended, or should I not worry about it? The bike frame is steel, from a quality manufacturer. I'm guessing that the non-drive side was faced when the shimano cartridge-type was installed, but I'm not sure about the drive side.

By the way, installation was a breeze. No issues getting the spindle through the bearing caps. I have to admit that Shimano makes some nice stuff. Although it kind of weirds me out only finger tightening the crank arm onto the crank spindle.

You can check for the need to face a BB shell with feeler gages. Screw each cup in until it contacts a .010 inch feeler and then use .008-.012 feelers to check for high or low spots. If no areas exceed thos limits, you're good. With the older cartridge style BBs it's the drive side that needs facing, not the nondrive side. With the new outboard cups, both sides may need it. Of course there should be no paint remaining on either face of the BB shell. If you didn't at least clean the faces, start over.

As for tightening the crankarm, the center bolt adjusts the bearing preload. It does not hold the crankarm in place. The pinch bolt keeps the crankarm on (most of the time).

I guess I got mixed up on which side was which with the cartridge bb. Thanks for the tip w/ the feeler gauge.

And I guess I'm going to err on the safe side and go get the shell faced.

Yeah, but after years of checking crank bolts for tightness, it's still strange :-)

A big For What It's Worth, since the following probably doesn't have anything to do with your frame:

I just received a new Felt frame. The instructions accompanying it specifically says the BB shell is "precision machined" and "with the exception of greasing the bottom bracket threads, ... does not require any bottom bracket pre-install preparation." ... "Do not face bottom bracket shell or otherwise attempt to modify the surfaces of the bottom bracket".

I wonder if your frame mfgr has anything similar?

Camilo: interesting...what material is the frame?

It's a full carbon fiber Felt ZC frame. The threaded part of the BB shell is metal (aluminum?) inside the carbon fiber. The faces of the threaded metal part do indeed look precision machined already.

Haven't put it together yet, so have no real life experience. (hopefully this weekend!).

That's really the way it should be with today's frames. I've been riding since the mid 80's and never had to face a BB shell yet. I now have three LOOK frames in the '04-'07 model years and all are fine with outboard bearing cranks and no BB facing.

I'm sure this is why the manufacturer explicitly proscribed facing of the BB shell -- the carbon surrounding the shell would be damaged. The aluminum insert was pre-faced when the frame was built.