valves from falling into the cylinder if the heads are still in the car if you dont have access to an air compressor is to get about a 2ft piece of rope with a diameter which is slightly smaller than the spark plug hole and push it into the cylinder making sure to leave about 6inches out (so you dont lose the rope) and put the cylinder up to TDC and then the rope will be tightly pressed up against the valve so you can remove the keepers without the valve falling. Pretty cool trick imo