Still Confused, Hydraulic Lifter Pumps Oil And Traps Oil?!?

Opie390 · Jul 1, 2019

ive been learnin a ton from your great posts in cam & valvetrain forum, lookin fwd to explorin rest of em. but anyway im still confused about hydraulic lifters:
how does the lifter both pump oil up the pushrod AND at the same time trap oil in its chamber acting like a solid lifter? is it RPM's vs the bleed-down rate(for lack of better term)of the lifter?
also i know my FE 390 doesnt pump oil up rod like other blocks so are the lifters designed a lil different?
and lastly the oil pumped into the lifters is never enough pressure by itself to overcome the valvespring, without the oil trapping mechanism am i right? it just maintains contact at all times. thanks.

Grumpy · Jul 1, 2019

ok, basics, the oil enters the lifter from block oil passages under pump pressure while the lifters on the cams base circle,
with near zero valve spring pressure on the lifter seat,
the hydraulic oil pressure lifts the push rod seat taking up the valve train clearance.
as the cam rotates the lifter moving up off the cams base circle causes the lifters push rod seat to momentarily move down compressing the trapped oil volume , as the push rod seat is compressed,down into the lifter body,
forcing oil trapped in the lifter up through the push rod,, the trapped , and now further pressurized oil is there for two different requirements,
first it lubes and cools the valve train, as it exits the rocker/push rods and flows over the rocker and valve springs,and second it quiets the valve train by removing the clearance, with a cushioned floating push rod seat,
that clearance is required for the valve train to function.
but the clearance results in a ticking sound like solid lifters produce,
adding a hydraulic supported push rod seat quiets the valve train,
and without the hydraulically supported push rod seat,the valve train requires periodic clearance adjustments ,
the hydraulic supported push rod seat is fully compressed, by the cam lobe forcing the lifter up against the push rod and the valve springs resistance,
by the time the cam lobe reaches peak lift ,
but at lower rpms all the oil is forced up and out of the lifter well before the lifter is near full lift on the cam lobe,
now it is possible that at extremely high rpms the lifter bleed down rate does not have sufficient time to vent all the trapped oil,
this is commonly thought to result in valve float,
but thats not likely, the inertial loads on the lifter and valve train not being completely controlled by the valve spring resistance,
and ability to seat the valve firmly and keep it seated as the lift returns to the cam lobe base circle,
and the lifter loosing firm contact with the cam lobe and or bouncing,
as it re-seats is far more commonly the fault.

most of the GIVE or clearance or movement in a hydraulic lifter push rod seat is the result of pressurized oil flowing into and lifting the push rod seat, without the pressurized oil entering the lifter body,from the sides of the lifter body from the oil passages in the block, manually forcing the push rod seat down into the lifter body is basically a one shot deal that generally only going to compress in a minimal .060 -.08 once until oil pressure forces the seat back up.

Still Confused, Hydraulic Lifter Pumps Oil And Traps Oil?!?

Opie390

Member

Grumpy

The Grumpy Grease Monkey mechanical engineer.