Originally Posted By: demarpaint
Originally Posted By: Shannow
Sonof Joe,
I respectfully disagree on some parts of your post.
Above is a cutaway of the Chrysler Hemi hydraulic lifter...like most hydraulic lifters (formerly referred to as "zero lash" if that shows my age), the clearance isn't reduced by oil pressure "pumping" the lifter, that quite big spring is supposed to remove the lash, then the oil flows in, and is captured by a Non Return valve inside the lifter body, and the oil being essentially incompressible makes the lifter "solid" on the upstroke.
A bad NRV back in my Holden/Chev days would make for a clattery lifter. If u ran it with the valve covers off, you could feel the impact loads as the zero lash ended up with lash...adjusting was back them off until they had lash (felt via placing your finger on the rocker and feeling the impact), then tightening down to zero impact, and a little more. A bad NRV always was bad.
The lifters "bleed" down between strokes, dependent on viscosity and RPM...cold start, and the few that were under load clattered like nothing else until they got refilled after a few seconds of oil pressure.
Later, some enterprising people started the high bleed lifters that bled down excessively at low cycle speeds (RPM), and made the cam effectively smaller duration and lift by bleeding down...at high RPM, due to the rates of theings moving, they couldn't lose as much oil volume as fast, and the cam timing returned to closer to the design.
Chrysler in their MDS system take it that much further...
Cut the oil to the cylinders that you want to de-activate, which implies an almost instantaneous bleed-down requirement, to allow them to be on/off...needs comparatively large volumes of oil to refill them too, and the regular bleed down rate must be necessarily high.
Also means that the roller, instead of following the cam profile is free floating, controlled only by the internal spring, which SHOULD be OK...but then when you starte to re-oil/refill, there's a number of cycles that "bang" turn solid mid way up the upstroke...at the point of maximum acceleration.
Engineering wise, that's bad Mojo.
So I sort of part agree, part disagree.
Interesting. I'm wondering if the people who disable the cylinder deactivation also have the tick?
I think that's a very important question, particularly given the wealth of information Shannow has just presented.