how do hydraulic lifters work

[eckertt@epri.co]

I have been told that when I shave 10 mils off of my Mopar heads to up the compression ratio, that the hydraulic lifters will automatically compensate for the change in distance (the 10 mils). I suppose I can understand how oil pressure inside the lifter can adjust itself to bleed off at some predetermined setpoint. What if stiffer valve springs are installed...how do the Hyd lifters know at what height to go to? Is there a nice paper I can read the covers this? Am I just dense, or have others wondered how hydraulic lifters seem to be able to make up for changes in head/block shaves?

Thanks Tim
eckertt@epri.com

[cuda66273]

No your not dense by any means,

A hyd lifter has about .090 of oil pressure cushion in it so as long a the valve spring doesn't exceed the internal pressure of the cushion it won't bottom out or collapse and as it has this fairly large variable you can usually cut a pretty good chunk off the head before you have to worry about shorter pushrods.

[pishta]

imagine a piston in a cylinder closed at one end. The piston is the piece that comes in contact with the pushrod and the cylinder is the part that fills with oil. Now you put a check valve in the hole that lets the oil in and oil pressure fills up the cylinder (lifter) pushing the piston right up to the pushrod. The oil pressure doesnt have enough PSI to act on the valve spring so it doesnt open the valve, it just pumps right up to the pushrod. now you have a tight lifter, no slop. Now when the cam lobe starts to push up on the lifter, it wants to squirt the oil out the hole, collapsing the lifter. The check valve doesnt let the oil out because it is a one way valve. now your lifter is in a sense a solid piece, with no compression allowed. Hi bleed lifters let some out at a controled rate to show the valve gear less lift and duration at low RPM' s, but that is a different topic. So at pressure the hydro lifter is just like a solid one.After you shut it down, the check valve will eventually seep a little oil out, making it clack when you start it up.

[eckertt@epri.co]

pishta, thanks for your answer. You offered just the right amount of detail. I now understand hyd lifters clearly. Thanks.

A new subquestion, several years ago at a MOPAR drag race show in Bristol TN, I attended a great Q&A session hosted by Herb McCandlis (sorry, probably misspelled), Ronnie Sox, and another guru that I can't remember his name. One of the gurus remarked that one should ONLY buy MOPAR hyd lifters, because others brands had made some lifters incorectly (did not elaborate.) Later, I asked another guru about this and he told me "not to worry - that "issue" is in the past, you can buy good lifters from any of the major brands".

Does anybody know the details about this "issue"? Just curious.

Tim
eckertt@epri.com

[John Kunkel]

One problem was the location of the oil feed groove around the lifter, some makers tried to make a one-size-fits-all lifter for Mopar and AMC.
With some cams that had a smaller base circle, the altered groove would become exposed and bleed off oil pressure.

[6 packin]

Yes all that and.....
The principle of all liquids are Incompressiable, no matter what force is excertec on it.