It is very strange, why would anyone reduce the size, it does sound like you need a different spacer, was the s/arm intact when you got the bike or did you get a set of bits ? 4mm is quite a lot, I wonder if the centre bush/spindle is the correct length, p/n, 52101-kv3-831 distance collar, it doesn't give the measurement but one of the guys will know.
If it was all intact when you got the bike and was correct have you lost a spacer somewhere.
A bit of a puzzle.
Dux. :
