The combination of the rubber O ring under the split valve keepers and the sheet metal shield over the top of the valve spring deflect oil away from the top of the valve guide. Enough oil should splash off the spring to lube the valve stem if the clearance is correct. Some people add a "positive valve stem seal" or an umbrella-type seal, but they don't eliminate the O ring and the sheet metal shield when they do. That starves the valve stem for oil, and the valve galls in the guide and/or sticks.
IT IS ABSOLUTELY ESSENTIAL FOR A TINY BIT OF OIL TO GET PAST WHATEVER SEALING SYSTEM IS USED!
The valve cannot operate in a bone-dry condition, especially if someone fits the clearance too tight. With the crankshaft locked with a couple of pairs of vise grips on the flywheel, air pressure can be put into the spark plug hole to keep the valves seated while the spring and/or seals are removed, or a long piece of sash cord or 1/4" nylon rope can be pushed into the cylinder through the spark plug hole, then the piston is pushed up against the cord by turning the crankshaft, trapping the valves in the closed position. Just be sure to leave enough cord hanging out of the plug hole to fish it back out! Most parts stores sell or rent an on-the-car valve spring compressor that can be used with the head installed.
Look up a K-D Tools #2078 valve spring compressor. It's the classic tool everybody else copied.
Jerry
