No sideways push on the valve stem. I shimmed my rocker shafts and they still need more work. But I don't have rollers. I didn't measure but I swear the valves I put in were longer stems.So a stability and durability purpose I assume?
And thanks, I tried to weed through all that on my thread but good heavens it was a dick measuring contest only it seemed they were all using the mm side of the ruler