My bottom bracket started to my make metal on metal grinding noises. Upon investigation, water ingress has degraded the bearings. The previous owner must have used a wench to remove/install the old bottom bracket, it was really done up tight! The bottom bracket face on one side has chipped paint, should that paint be removed by bottom bracket facing?
If you have a few quid free for facing, spend it.
Having a smooth, flush and parallel metal surface for the bearings to sit against is likely to extend the lifespan of a BB by preventing any deformation of the races and pressure spots. It's also likely to stay tight in the frame with less force, meaning you are able to fit it with lots of anti-seize [not grease, esp/ not PTFE grease], not over torque it and still have it come out again without a scaf bar and the biggest bloke in the LBS sitting on the end of the lever.
The threads will also be chased, so that's handy as well.
Water getting into your bearings has nothing to do with how faced the BB shell is. Mostly the BB face isn't going to have any effect. The threads need to be parallel. A teeny bit of paint will make no difference to how much water gets in.
It won't change water ingress, but will help extend BB life by keeping the bearings parallel. All BB brands recommend it to be done.
The previous owner must have used a wench to remove/install the old bottom bracket
There is your problem right there. The old owner should have used a mechanic rather than an 18th century prostitute!
A good smear of waterproof grease on the threads will stop any water going in via the threads - which is probably the path of most resistance anyway.
Getting in via the seat tube or drain hole, other holes etc is probably more likely or attack from the outside through the seals which is where badly designed BBs fall down.
but will help extend BB life by keeping the bearings parallel
facing will not do this. if the threads aren't already parrallel then no amount of facing with resolve it
nickc
I've never come across a frame where the threads weren't parallel. Plenty where the faces aren't though.
The process of facing should include chasing the threads - the tool that does that would highlight if the threads were not parallel. The faces are then prepared perpendicular to the threads.
It's pretty thorough, and worthwhile.
not grease, esp/ not PTFE grease
Why?
As for threads, there's some play in the cup when threading in, so it's the faces that need to be parallel.
But hasn't facing died a death? Bar say removing paint.