Dumb question here. Been riding 30 years (have '67 FLH and a '10 FLHTK). Just got a 2005 chopper with a 113" S&S. It has a soft "button" feeling thing in the center top of each head. I'm guessing these are manual compression relief valves. If so, what is the best way to use them? If not, what the heck are they?