Stem Riser - Headset adjustment?
 

Ok, I have an older Schwinn Mesa GS MTB. I ordered a Delta Ahead Stem riser - raises the stem and handle bars about 3" - for better posture commuting. When I take the stem off to put this on, do I need to do anything for the headset? I'm not sure what function the center cap that's in there now performs, whether it's just a filler, or if it has an expanding star washer that locks inside the fork (like on the really old 3 speeds I used to mess around with). I guess I'm just trying to be sure I don't need any additional parts before I start taking the bike apart.

Any ideas?