Quote:
is there any way a hydraulic lifter can push valve higher under actual running oil pressure compared to oil pressure during testing?
Packard's info on troubleshooting noisy lifters for 1940 cars has a minimum value of 3-4psi in the lifter gallery at idle and 20 during normal running speed. Those are generally the typical gallery numbers which are lower than main gauge readings as mentioned in several bulletins over the years. They settled on 5 psi at idle after several oil filter plumbing changes in 40-41.
Not sure how you did your testing for height but if there was not at least a minimum constant idle pressure maintained in the gallery, it is possible the normal lifter bleed off was fast enough to drop the valve and give a false reading.
On the other side, while it's not a likely cause, lifters can increase over design specs if the valve spring is weak or if the gallery pressure is too high. That was another spec Packard mentioned -- not to exceed 55 psi on the gauge for an extended length of time. Doing so could cause the lifter to pump up.
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