All correct Jerry, except the oil that bleeds past the piston is not lost externally on a 235. The oil is caught by the groove around the piston and directed, through a hole in the piston, back into what I would call the reservoir, ready to drop back down through the check valve, into what I call the working area, when the spring in the bottom pushes the piston back up.
This is where having some type of vent comes in to play. If all the air is not correctly bleed out of the lifter when installed, the air is trapped in the reservoir. Then just as the lobe is starting to let the lifter down and the inertia is sending the oil to the top of the reservoir, what is ready to go through the check valve to recharge the working area is air, making a soft and noisy lifter. This is what gives high RPM lifter noise. Once the engine is run at an idle for a short bit the air bleeds back past the piston back into the reservoir. Venting clears up this common problem. I discussed venting in a previous post.
