Much has been written and experimented with to resolve this recurring
problem. Apparently air is entering the lifter from the inlet
side of the oil pump or other source. Different lifters, sealed pumps,
sealed pick-up tubes & sealed by pass circuits have had much success but not
100%.
After trying many of the above fixes, Grant Galbraith found 100% success by
providing a small vent on each of the offending locations. Locate the
noisy position and remove the lifter. Wipe with lacquer thinner and
tape off the hole on the side and the entire top. Using a bench grinder,
grind a "flat" on the outside of the lifter between the annulus and the top of
the lifter. Grind about .005" deep. This will provide a "vent" for
any air collecting in the lifter galley so that this air does not enter the
lifter and cause it to be "spongy" and noisy.
Oil pressure will only be reduced by approximately 1 PSI.
Tom Langdon