Prevent Big Block Chevy Lifter Oil Starvation
The Generation IV big block Chevy needs to have the front lifter oil gallery plugs modified by removing them and drilling a .030” hole in the center of the plug and then re-installing them. This hole will bleed off any air locked in the front of the galley oil passages. This air lock can cause the front lifters on both sides of the block to starve the oil supply up to the rocker arms, plus starving the lifters causing them to clatter.
GM started drilling the plugs in the late 70’s to early 80’s and produces a change bulletin to modify any older engines that were being rebuilt or had a complaint of dry lifters in the front of the engine. The oil that will now be coming out of these holes will also help lube the timing chain and gears as an added bonus.
Source- Crane Cams Newsletter Issue 202