Think about the few thou of play in a thread. You snug the bottom nut down and it sits with it's threads UP against the stem threads. Now you put the upper nut on and tighten it. It pushes the lower nut down (paired locknuts always push themselves apart to lock).
So as they push apart the lower nut is putting more force on the stem bearings, tightening them up. That is why you have to start out with the lower one looser to allow for the movement due to thread play.
__________________
2011 EC250E
|