I've been going through my GMC 270 (Civilian Block) and found that 1 of the 12 lifters doesn't match. The offending lifter has a hole in the pushrod cup as well as a hole in the side body of the lifter. The GMC 270 uses solid pushrods; according to the manual oil is pumped up through the cylinder head to the rocker assembly. I consulted my GMC Maintenance Manual (X-5703) and cannot find any picture of the lifters. Question 1: Which lifter is the OE type? Question 2: Is this a 'much ado about nothing'?
No oil being pumped to the lifter, so who cares? But none of my GMC engines had holes in the lifters.
I've had and used both. If they had a hole in the top and the side, the oil coming down the push rod filled the inside of the lifter to the side hole. As the lifter spun it continued to splash oil out of the side hole to oil the lifter bore. This may have been for extra oiling in severe duty engines, just a guess. These are also heavier because of the oil stored in them. Oil from the rocker system also oiled the lifter gallery. The ones without the holes on the top or sides got all their oiling from down the push rod and the holes in the head to the lifter gallery and was totally a splash system.. Oil spun off the crankshaft oiled the bottom. of the lifters protruding thru the block above the cam lobes. All oiling needed the correct valve lash to work properly. GMC's had one hell of an oiling system for a 1940 release and were made for heavy duty hauling.
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