I need you guys to help me understand this lifter "pump-up" phenomenom.
I can understand why, at very high revs, there is not time for excess
oil to escape from the lifter, and thus for it to pump up. By very high revs I am talking outside the normal range for hydraulic lifters - 6500+.
However, at normal revs, with engine
oil pressure at 75lbs max, I calculate the "closing" force exerted by the lifter on the pushrod to be in the 15-20lbs range (I assume 0.5" dia of the "piston" within the lifter, probably a way out, but good enough).
Now how could this lift valves off seats?
If the preload were to be so excessive that the lifter bottomed out internally, that I can understand would result in valves being held off their seats.
As engine temps reach normal, the preload should lessen (given ally heads) since the heads would expand more than the steel pushrods?
Someone give me a steer here, this is interesting stuff, and I am but a poor ignorant englishman.
