Facing to remove paint
 

Finishing up a restore on a classic Bridgestone. The frame has been powder coated. Can excess coating on the BB shell faces and head tube ends simply be removed with a sharp utility knife or is it advisable to take the frame to a shop and have the surfaces refaced with a tool for the job? I imagine the BB and head tube were surfaced when the frame was made 27 years ago but maybe not...

I carefully do it with a flat file. If you're not confident that you can maintain the right angle, then any competent LBS should be able to do it for a reasonable cost.

A utility knife is less likely to remove metal than a file. A decent file is an actual metalworking tool and can remove metal and alter the faces. That being said many frames did not come faced from the factory. A minor cost cutting measure few notice until it’s time to rebuild the BB.

However, there’s another solution to facing bottom bracket shells, using a cartridge square taper BB. The bearings come aligned in the cartridge, the unflanged cup doesn’t even touch the faces, and the flanged cup just bottoms out and is held in alignment by the other cup. Facing BBs for cartridge BBs can be detrimental even because raw steel is exposed to the elements. They also require less frequent service, preserving your crank tapers, and replacement is easier than rebuilding.

Sandpaper on a block to keep it flat and easy

^^^^ I would add the following fill the opening with a paper towel to limit grit from falling into the BB and HT, clean well after sanding.
One other thing, push the block towards the opening in order to minimize any flaking of the PC.
Best, Ben

Yep, a cartridge BB sidesteps the need for facing. Facing was done during the loose cup era because it ensured that the two BB cups were perfectly aligned with the spindle bearing. If a self contained cartridge is used, facing isn't really necessary. Even so, I'd be inclined to remove excess paint with a utility knife, to get a good seat for the drive side BB flange. Not strictly necessary though. If a traditional BB is used, facing is standard practice and a good idea for top end bikes. It wasn't usually done on mid or low level bikes, because they wouldn't be ridden enough to matter.

If it's a flange-less cartridge Phil Wood, no need for that. Leave the paint.

Thanks to all for the advice. I took the frame to my local bike shop. They are facing the head tube, seat on the fork crown, and the drive side of the BB shell for a cartridge bearing. They recommended the drive side only be faced to avoid cracks in the BB cartridge.

Having been in this same situation, my experience was that powder coating creates about three times thicker layer than normal paint. Good for durability but not so good for mounting surfaces like BB and headset. Even with a cartridge BB, it is necessary to face the bb shell to get a good seat with the fixed "cup" side. And if your cartridge bb uses lockrings on the adjustable side, you'll have to face there too. I originally mounted the BB (Shimano UN-91) without facing the fixed side and the gap was so significant (even after cranking down) that water and grime got into the bb through the gap and then the threads. When I pulled the bb a year later, I had surface rust. Ended up with much more work to clean that mess up. So good call on getting the facing done before all that nonsense happens.

I don't understand. Just use acetone and carefully wipe at it. Acetone will dissolve powdercoat and get you back down to base metal. Just don't drip it over onto other spots that'll be seen. (MEK will do it faster, but it's super nasty stuff!)

It's not just a matter of the paint. The point is to machine the ends of the BB shell perfectly square, so that when the cups are screwed in, they are perfectly perpendicular to the spindle. To properly face a bottom bracket shell, you turn the facing tool until any paint is removed, and then continue turning until there is fresh even metal all the way around. Might take a half a turn, might take 3. Stop. Many BB shell were surprisingly uneven on the ends.

For a cartridge BB, removing paint is enough.