Originally Posted by
FBinNY
If the original headset fit and worked properly, it's reasonable to assume the frame and fork were properly prepared. Machining it anew can't make right righter, but there is the potential to screw it up.
Best practice is to follow rule number one -- "don't fix what isn't broke.
As long as the new headset is the same standard as the original, ie ISO vs. JIS, it's a straightforward, pop out and replace.
+1 on all of this. If the current headset is smooth and doesn't bind, the facing is very likely fine.
Since this is a 1-1/8" threadless headset, the ISO/JIS difference isn't an issue as all 1-1/8" press-in cups and crown races are made to the same standard.