NOISY HYDRAULIC LIFTERS ON CHEVY 235, 261 Rev. 20 Sep 2010 bas
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″ to .007″ 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 at IDLE (If all 12 lifters are modified)