Fred, after reading over I realized I was vague and asssumed everyone knows about the 235 hydraulic lifter problems. I don't believe there is a problem with the lifter itself but rather the design of the 235 oil pump. It isn't submersed in oil so any leak on the suction side of the pump results in air in the oil supply. Lifters don't like air. It usually manifests itself a noisy lifters that can be heard right after a highway run. Let it idle a couple minutes and it quiets down. I tried leak checking the pump by pressurising and checking with leak tech or soapy water. I sealed the inlet threads OK but noticed the pressure relief valve leaks. In theory this should not be a problem becuase I would assume the valve will be pushing out excess oil pressure, not drawing in air but 2nd time around I threaded it and ran a tube down to submerse in oil. Still noisy. For some reason the air seems to go two one or two lifters. In my case it was one at # 3 cylinder. This is when I tried Tom's idea of grinding a flat on the top half to let air escape. Seems there is a GM v-6 out there that had this done at the factory to quiet lifters. As I said it seems to work for the most part, but there are still times I think I hear some clacking.
