Just dragging an old bike into this century with a slx 10 speed set up.
It currently has a square taper in there. When putting my new bb in will it be obvious if the frame needs facing ?
Probably not.
(Possibly contentious comment) I don't see the point of facing for almost all bottom brackets - much more important that the threads are parallel.
it'll be obvious when you put the axle through.
I spent a lot of time searching the WWW about this when considering going HTII.
It seemed that those who knew what they were talking about found that it wasn't generally needed, and those HTII premature bearing failures that had been attributed by many to be due to an un-faced BB shell, were actually failures due to way too much pre-load.
I've just built up an Uncle John and the BB shell looked quite noticeably on the wonk. The chap in my LBS said that it is rare to take off as much material as he had to when facing a bike frame. For that bike I'm glad I had the facing done.
For my Cross Check I never had it done and the same bearings have worked faultlessly for 3 years.
Okay, here's my reasoning:
With HTII etc, there's nothing to keep the bearings in line, unlike with a square taper cartridge BB. The bearings screw into the shell. Now I can't possibly imagine how a cartridge could screw in straight, but then suddenly go squint once it hits the face of the shell - unless the threads are completely worn away, it's just not possible for the bearing to end up squint that way. SO the only way the bearing could be squint is if the cartridge was deforming, and I can't see that happening.
So misaligned bearing can only happen if the threads are not parallel.
bencooper - Member
Now I can't possibly imagine how a cartridge could screw in straight, but then suddenly go squint once it hits the face of the shell
really? When I screw in a BB cup, there's a bit of play, so if the faces are squint (which I'd guess is more likely to be about paint than metal), the BB cup can align to them. Whether that's enough to cause bearing issues, I don't know.
Hmm, interesting, I don't think I've ever seen one that loose - okay, so if the threads are relatively sloppy then I can see how it could matter.
Of course the whole thing is silly anyway as there's nothing wrong with square taper 🙂
Facing not required but you need a rock to install the new BB properly
Its gone in but it doesn't spin forever like my old one.
Ps the frame is raw so no paint to worry about.