The keeper goes in the top groove and an 'O'ring oil seal goes in the lower groove, fitting against the bottom of the keeper. If I remember correctly, the original valves had only one groove, and an umbrella cap went over the valve tip and spring retainer to serve as an oil shield. That changed in the 1950's, but I don't remember the details. Perhaps someone else can fill some details. Memory is kind of foggy on that topic, but I think the intake valves had two grooves and the exhaust had only one- at that time (pre-historic times) it was thought that oil wouldn't leak through the exhaust valve guides. Which was proven to be a false assumption.

Harvester