is this correct?
at high rpm, the springs arent completely pulling the the valve closed (what springs, why, and what rpm, is a separate topic)
meaning that for some amount of time, the cam lobe ceases to touch the roller on the follower, presumably immediately following the peak of the lobe
in that moment, the lifter rises, closing the gap
but what that now means is that when the cam is at that same position, the valve will be open further than it should be, since the lifter has now extended beyond the point required to keep the lash at zero.
the phrase "pump up" suggests that this occurs incrementally over some number of cam revolutions..not important really...
question: is this lifter over-extending a guaranteed outcome of spring induced float on any engine with hydraulic lifters? Or is there a separate phenomenon of float where the lifter does not over extend? (solid lifters?)
Let me ask that a different way:
Solid lifters would not solve this problem, because the springs are still not closing the valve soon enough, so there would still be float. Right?
And a third way:
So how does the situation differ assuming everything is the same but one has solid and the other hydraulic?
I am guessing the that hydraulic lifters extend the amount of time the valves remain in float. I.e. even after the rpm drops to where the springs can keep the valve closed, they are kept artificially open until the lifters bleed out (doesnt that require engine-off?) So there is "spring only float" which happens at high rpm when the springs cant do their job, before the lifters have pumped up. "Combined float" which is at that same rpm after the lifters have pumped up, and the springs are still/would be floating. And "lifter only float" when the engine is back at a lower rpm where the springs could do their job, but the lifters are now over extended, causing the valves to stay open further than they should. (how long does that last?)
Okay and another question...what springs/cam/rpm are known to experience this, and why are the springs too weak? Is that something that can be identified from the cam profile + spring characteristics?