Its hard to get an exact measurement. I used a piece of 030 mig wire to try ad get some sort of idea and the gap is no bigger than the wire. I do not really understand what exactly gets ground on the cam. The base circle on the cam is the under side of the lobe and if so how does that lower the lifter in the bore when the lobe lifts the lifter. Or does it get ground where the cam bushings ride which would mean over sized cam bushings. Can someone explain this to me (simple words,lol)