I'll assume you have set valves before as I type this out. With the lifter
on the base circle, and valve seated, you install the pushrod and place the
rocker on the rocker stud.

You turn the locking nut on the rocker arm until all of the up and down
movement has been removed from the push rod. This is called zero lash.

At this moment, the lifter seat is resting against the retaining clip and
there is no preload. Everything is relaxed so to speak.

The next step is to set preload. You begin turning the rocker adjusting
nut until the pushrod loads the seat. Since the valve spring pressure is
higher than the plunger spring, the rocker will deflect down on the left
side of the centerline and the pushrod will move the lifter seat down
(let's say 0.040").

You have now just pre-loaded the lifter. With the rocker nut turned down
about 1/2 turn from zero lash, there is about 0.040" preload. There is no
slack in the assembly.

Let's say you prime the oiling system at this time (the engine does not turn).

The oil fills the passages and enters the lifter chamber. The oil pushes up
on the plunger and seat assembly with "X" amount of force. We'll use 60
pounds for sake of a number.

Nothing has moved. The lifter seat is already loaded. No movement is made
in the valve train because there is no slack.

At this point in time you have 60 pounds pushing up, and an equal force
pushing back. The spring is only exerting a small amount of energy to
maintain an equal and opposite force.

60 pounds pushing up, and 60 pounds pushing down. The forces are equal.
Nothing moves. No work is done.

If you were to turn the engine over by hand at this time, the lifter will begin
to follow the cam lobe. Since the lifter is full of oil, it is essentially solid and
cannot be compressed.

As the lifter follows the lobe pattern, the valve begins to rise and you feel
resistance from the compression of the spring.

Now there is an increasing dynamic load as the lifter ramps up and the spring
is compressing further. The lifter is still pre-loaded, there is no slack in the
pushrod.

You now have 200 pounds of force on the lifter seat pushing down, and
200 pounds pushing up (oil cannot be compressed in the chamber). The
valve lifted because of the energy you exerted when turning the motor over.

At this time the lifter is high in the lifter bore and disconnected from oil system
pressure.

You continue to turn the motor over, and lifter is on the nose of the lobe.
With the rocker ratio and fully compressed spring you now have 400 pounds
acting on the seat (down) and 400 pounds acting on the seat (upward).

Since the net force is zero, there is no additional lift. The preload is still at
0.040".

Turn the motor further; the lifter comes back to the base circle. Spring
pressure is reducing. The oil in the lifter is still maintaining a 'solid' internal
mechanism. The force pushing up and down is still equal. The only external
forces used to lift and lower the valve are coming from you as you turn
the motor over.

Now the last stage. The lifter is on the basecircle. The pushrod is still
pre-loading the lifter down 0.040". This time you have some bleed down
because of the spring pressure and the lifter holes are aligned with the
oiling system.

If the valvetrain did not wear down, the preload does not change. The chamber
should be full of oil.

The oil system pressure is less than the spring pressure, so the oil will
move to the area of least resistance (lowest pressure). If there's no
void to fill in the lifter chamber, the oil pump pressure will cause the fluid
to move up the pushrod and oil the rocker and spring.

And the cycle repeats.



These are good points. valvetrain harmonics and rod flexing contribute to
loss of lift. The function of hydraulic lifters lends itself to poor valve repeatability
as you mention.

Having the correct preload and components for your set up can help reduce
these losses...or we can just throw in a solid cam/lifters and get instant
power increase.

 

At this point in time you have 60 pounds pushing up, and an equal force
pushing back. The spring is only exerting a small amount of energy to
maintain an equal and opposite force.



Ding Ding Ding.. We said the same thing..

 

With all due respect, you contradicted yourself in that paragraph:

If you meant otherwise, then cool...let's move on. I think we've covered
everything there is to know about basic hydraulic lifter operation.

 

Hey I just wanted to say thanks to both of you for giving me some things to think about and sorry for causing the argument heh It was very educational thou.

I did pick up some valve checking springs and gonna get to that next weekend. Hopefully my parts store has the length in stock so I can complete assembly and get all my parts off the benches and move on the the dif and tranny.

 

Way back in post #3...

"When you measure the pushrod length for your type of rockers, you will
adjust for zero lash (yes, lash) with the rocker tip resting on the mid point
of the valve stem."

Are you saying check pushrod length with no preload and only zero lash set?

Also, wouldn't you want the roller tip set slightly inboard, so that the wipe pattern would be centered on the stem?

 

To account for 'pump-up' yes, especially on tight clearance set-ups.

It depends on the rocker design. Ideally, you want the most valve lift,
and velocity out of the motion.

If you can setup the rocker arc such that it starts inbound
and finishes mid point, that *should* promote the fastest valve velocity
(in theory).

The more it stays in the middle of the stem, the less loss will occur.

The only way to know is measure it out (something like the rig shown in the
photo earlier with the dials) on your actual valvetrain.