When the valve cannot follow the lobe pattern due to incorrect spring
pressure, or high RPM the valve will float.

If the valve floats, or bounces the lifter will pump up the amount of
pre-load initally set...because the seat is no longer loaded.

Now that the seat has pumped up (let's say 0.040"), the check ball
will lock the oil in the chamber with the seat pinned, and when the
valve comes to rest, it's effectively sitting 0.040" higher in relation
to the cam lobe base until the next cycle when the lifter bleeds down
due to the valve spring pressure/loading.

Close. It's not the oil pressure lifting the valve. It's the oil pushing up the
seat taking up the slack caused by valve float, or bounce.

It's just a matter of maintenace. That's it. If you set the preload at
0.050" you can expect to reset the valves sooner due to valvetrain wear.

If you set the preload to 0.150", you can expect a longer service life
with a trade off in performance and engine vacuum.

Think of this another way (a question for those who still believe oil is lifting
the valve):

Why set any preload at all if the oil pressure is just going to push the seat
to the retaining clip and lift the valve?

Also ask yourself when in the lifter cycle this happens.

Because hydraulic lifters vary the seat position throughout the engine
rotation. Oil is escaping due to valve spring pressure (bleed) and then
refilling to take up the slack.

It's a sloppy system overall, and causes the valve closing/ramping to
delay itself to the intended phasing.

With a solid lifter, the seat height never changes and the valve phasing
is the same every revolution of the crank. The valve is accelerated as soon
as the solid lifter begins to rise on the cam lobe.

In a hydraulic system, this isn't the case due to the oil escaping and refiling
each cycle.

Only in float/bounce conditions. That is the only time.

Look at the oiling system diagram of an engine and have a look at the oiling
hole in a lifter.

There is only a small time frame in the travel of a reciprocating lifter when
the oiling system pressure has access to filling the lifter chamber.

Another thing to realize is that 60 PSI is not going to lift a valve which has
a seat pressure of 130 pounds * the rocker ratio.

Another analogy for this: teeter- totter. If you place a 60 pound weight
on one end, and a 130 pound weight on the other, how much lift has been
achieved?

Don't forget, the fulcrum of the teeter-totter is not central and acting against
you even more.

If I find more literature on lifter function, I'll post it up.

 

I hope they locked out the hydraulic mechanism before doing this.

It's true engine builiders will modify the lifter in race classes (if allowed)
to make the lifter act solid and also reduce mass due to less oil.

However, if you set massive amounts of pre-load in an engine with
stock hydraulic lifters you will kill performance and run the risk of
clearance issue (coil bind) in the event of 'pump-up'.

Here's a supporting article that explains what I'm referring to:

http://www.4secondsflat.com/Hydraulic_lifter_cams.html

 

http://www.compcams.com/technical/FAQ/FAQLifters2.asp

Anyone care to guess why the competition lifters only require 0.002"
for preload?

 

OK, last one and I hope I've at least made some of you re-think how
hydraulic lifters function. If not, good luck to those setting massive
amounts of preload looking for good performance. If my posts, or the
seven articles haven't changed your mind...nothing will.

http://www.ratwell.com/technical/HydraulicLifters.html

 

Ok.. Time for my gun again This is actually fun You ready for me to present holes again Please don't mind the fact that I moved some of your points with that were similar that I'd like to argue on. And please don't take my comments personal as everyone has something to learn from this discussion. Myself included.




Agreed you will see valve float here. Another cause would be a lobe profile that is overly agressive for the spring/rpm range.



What is the surface area of the plunger that the oil comes in to contact with?
What is the surface area in which the valve spring contacts the head/retainer (and don't base it on the OD of say 1.29" since the spring has no center, it's a lot less than that. In addition, probably need to figure on the outer spring if it's a dual spring set up as there really isn't much on the inner spring a 1.80")
Is there more surface area with the plunger or the valve spring?
This is going to determine if the oil pressure on the plunger has effect on the valve spring while the valve is on the seat.

For example, if the plunger surface area is 1 sqaure inch and is seeing 60psi but the valve springs diameter is say .75 square inches, the valve spring would have to at least 80lbs of seat pressure to over come the plunger rise. Do you agree with that?

This needs to come in to the equation just as much as rocker arm ratio.




Right, and this is where I mentioned having more preload reduces the void the oil needs to fill inside the lifter. Fluid can only move so fast. 3 ways to fill a void faster, keep the same pressure but give it a bigger hose, put more pressure through the hose or make the void smaller Since you can't change the size of the holes in the lifter that fill it, guess you need to add more pressure to fill it back up faster, heck making the void smaller might help too. Oh wait, I said that



Wait a minute.. Haven't you been saying that oil pressure has no affect in plunger depth? If it's bleeding down, effectively lowering the plunger in the lifters body, how is it ever going to refill and raise the plunger back up? You are telling me it is loosing all of the oil pressure that built up inside of it through bleed down? Not possible.

You are also adding to my arguement with this last statement. Through bleed down you are loosing pressure in the lifter, are you not? As it cycles back in to the oil gallerey it recoupes it's lost oil pressure lifting the plunger again.





Right, again where more pressure is going to allow you to fill that void in the lifter in a shorter time span. If there was very little oil pressure to do so, you would not have the volume to refill it, lowering the plunger depth the higher you spun the motor.

 

One thing you have to realize is this is not my theory. THis is fact.

I've linked several credible links from race sites and even Comp Cams
tech page. I'm not going to argue this, but I'll help you understand
that oil pressure does not lift the valve - ever.

No, none of this applies.

The pushrod is applying a force on the lifter seat. All the spring pressure
and calcs. you have done for the retainer should be focussed to the lifter.

On one side of the lifter seat you have 60 PSI * surface area. On the
other side of the lifter seat you have 130 pounds * rocker ratio acting
against an even smaller surface (the pushrod contact area).


Convinced yet? Have a read through those last three articles if you haven't
already.

Not at all.

Right. Only until it takes up the slack from the amount you turned the rocker nut down.

Once that slack is taken up, that's it. The oil doesn't lift the valve.

The seat returns to the original position you set when you turned the rocker adjusting
nut.

 

I see what you are saying..

But you have to keep in mind that the surface area the pushrod is seeing, is seeing the total force of the plungers pressure (psi of the full surface area), just like it's seeing the full force of the spring pressure through the rocker arm (the psi at the tip will be higher than both the plunger surface and the spring seat/retainer surface, simply because it is a much smaller surface. Tthink of a woman in a high heel stepping on your foot. 120lbs is a lot more through that ½”). I also agree due to leverage of the rocker arm, the spring force at the rocker tip over the valve will be less than side with the push rod.

In theory, you are saying that as rpm increases you are going to see bleed down of the lifter, resulting in less lift as the rpm increases and that you will never overcome that loss through oil pressure against the plungers surface.

I'm not completely discrediting what you are presenting nor and I saying the links and research of others you have provided is inaccurate. I'm simply trying to point out that I believe you will have less degradation of valve lift in the upper rpms if you put more preload in the lifter. I agree that this could cause pump up issues hanging the valve open once you reach valve float (tossing the lifter off the lobe of the cam, filling the lifter with more oil).

This is where I am saying if the void is smaller, than you will be able to maintian a given pressure in the lifter easier since there is less volume to fill.

Perhaps the guys that are making more power setting the lifters with more preload are bottoming out the plunger in the higher rpms through bleed down, not allowingthe lifter to colapse further, resulting in less lift degradation.

 

No, I'm not saying that at all. Never stated any part of that.

Sorry, I'm done with this for now. I've done the research, I've had the
mentoring, I've applied on engines and I have sourced credible links.

If you care to learn more, try this site:

www.speedtalk.com

There you will find veteran racers, engine builders, designers, etc.

When you start the thread, be sure to PM me the link and I'll be happy
to participate.

Perhaps someone over there can explain it better than I can here.

 

Wow what did I start heh

I'm no expert by any means,... hence asking a simple question to start,.. but I am able to logically think about this too with my mechanical knowledge. If my opinion counts for anything I happen to agree with both of you. And I'll just restate what has already been done.
Oil Pressure does not lift the valve it only fills the lifter. Once the lifter is closed the 'now stiff' lifter pushed the pushrod to open the valve, oil pressure can't affect the closed lifter because, well it's closed. But because the lifter only has a certain amount of time to fill I would think that more oil pressure would fill a lifter with less preload more effectively (larger cavity). Does that make sense?

I don't know this maybe completely out in left field but, if one is running less oil pressure from a stock pump say, they should run more preload because less oil pressure would keep up with less oil demand in the lifter. On the other hand an aftermarket pump could produce more oil pressure and you can get away with minimal preload because more oil can enter the lifter in the same amount of time.

heh Theres' my over tired idea for the day after another long night.

 

Pretty much bang on for paragraph #1, good job.

For paragraph #2, your theory seems fairly solid however I cannot confirm
whether it will improve performance by setting more preload.

I would hazard a guess and say that even 30 PSI would yield enough
pressure to fill the lifter chamber and still allow for a conservative setting.

I'm not aware of any data that supports such an experiment as everyone's
goal is to build the engine with required clearances and oil pressure.

Based on design, if the plunger sits too far down in the cavity, the oiling
holes wont align properly and cause a restriction of fluid flow. This is my
reason for wanting to maintain a lower pre-load, or at least maintain a range
within the MFG spec.

 

I know you were done, but




Funny that you now give him a plausable for his theory, but won't with me, when his point is exacly one of the points I have been making. I addition oil presusre has an effect on how much lifter bleed down you will see at rpm resulting is less gross valve lift.

Less oil pressure to fill the void the short amount of time = more bleed down, resulting in less gross lift, killing top end power.

Same oil pressure, smaller void = the void being filled faster might substain full valve lift or will at least degrade the lift less..



Consider this:

Once you have established oil pressure the lifter plunger is locked solid. (This we both agree on) [I won't go any further than that for now]

As RPM increases you start to see some bleed down since the lifter has a very short time to refill. This would be most prevelent in a cam that has large amounts of lobe lift, as the lifter band (body oil groove) can get pushed above the oil gallerey briefly. (Do we agree on this? If not, do you at least see the arguement I am making here?) [I think the band size and lift of the cam is going to be the key elements here]

As the lifter is bleeding down, the plunger hole could drop bellow the lifters body hole. At this point the oil has less ability to bleed out. (Can you see the point I am trying to make here? Do you feel it is plausable?)

In addition to the last point, as the lifter is cycled on the cam lobe, perhaps as it comes back to the base circle of the cam and the valve closes, the lifter plunger rises slightly as the forces decrease with lobe lift, just enough to get a little oil to reastablish oil pressure in the void in the body. (Do you see the logic behind this?)
[This is not something I am fully convinced of, but I think it's a possiblity, that's why I threw it out there in the first place. It's going to depend which force is greater, surface area of the plunger with a high oil pressure behind it vs the spring pressure through the rocker arm at low lift, IE seat pressure]

 

"Based on design, if the plunger sits too far down in the cavity, the oiling
holes wont align properly and cause a restriction of fluid flow."

Didn't think of this, Makes alot of sense thou. It could reduce the amount of time the lifter has to fill up. I should take one of my LS1 lifters apart and compare them to my LS7 ones that went in. Then see if the preload specs are the same.

Now said this, Do the springs inside the lifters really collapse over time or do they fail due to the lack of oiling requiring the spring to do the work instead of the lifter as a hole design, of course caused by inappropriate amount of preload.

I'm staring to think now that the reason lifters have different specs for preload is to keep the oiling passages at optimum working range, as different manufacturers may have different designs for oiling passages. I used to think the internal spring had more to do with it but maybe not so much.

 

I'm not taking sides, believe me. It's just that you insist that the oil pressure
will lift the valve no matter how many articles, explainations, or figures of
force that I seem to present.

Considering pressure/volume of oil, yes...it's a given that more volume and
more pressure will result in more fluid entering the chamber within the same
amount of time.

If you draw this out on paper, it will become very clear.

The oil on the inside of the lifter is pushing on the plunger/seat which is less
than one square inch @ 60 PSI.

The dimensions of contact area for the pushrod are much smaller than the
plunger/seat, and so is the valve stem tip.

It is also forcing the seat in the opposite direction with the valve spring open
pressure * rocker ratio. This amounts to somewhere in the area of 250 pounds
over the surface area of the pushrod (depending on valve spring and rocker design).

I don't understand why you believe these forces stop at the valve retainer;
the fulcrum of this assembly is the ROCKER TRUNION.




Anything on the left side of the rocker trunion centerline is receiving force
of the oil pressure when the lifter is ready to receive the system pressure.

Anything of the right side of this centerline is feeling the force of the valve
spring * rocker ratio somewhere between seat pressure to open pressure
depending on the position of the cam lobe.

Never at any point in the engine cycle is the valve spring load less than
the opposing pressure created by oil unless there is a valve float, or valve
bounce condition.

Lastly, if you still want to believe your theory. Answer this:

If oil pressure can raise a valve, why set preload at all? What is going to
take up the slack when the seat is pinned against the clip and the valve
train wears down?

 

Probably a combination of both and other factors beyond this discussion.

A spring will lose it's ability to maintain coil strength after heat and comrpession
cycles. This would be a good question to ask tech support/engineering
at a valvetrain MFG.

The spring is there to hold the check ball and plunger in place. If the
spring were to fail, the check ball would not seal the chamber properly
and the lifter will collapse.

 

Did I ever say the pushrod doesn't see the force of the valve spring through the rocker arm? No.. I said the push rod sees both the force of the valve spring multiplied by the rocker ratio and the force of the plunger (pressure that is in the lifter). When the valve is on the seat,the push rod only sees the pressure of the plunger/oil pressure. I have stated that the force of the plunger side of the push rod will change based on oil pressure and that if that pressure force was more than the valve spring pressure mulitplied through the rocker, then and only then could you lift the valve. I stated there would have to be enough oil pressure against the surface area of the plunger. The reason I asked for surface area of both the valve spring and lifter. You can't figure out the mathmatical equation with out it.

Come to think of it though, you'd only need to know what the installed spring rate was and the plunger surface area.

 

Then how can you think the oil pressure is capable of opposing the valve
spring force?

That would be true only if there was zero preload. That is not the case.

Fine. Then, do you now see the valve can never be lifted by oil pressure?

You don't need to know the valve spring area; you need to know the valve
stem area and rocker tip area. The rocker tip contacts the valve stem which transfers the force.

 

This is a dynamic situation, the lifter deflects and changes shape, the pushrod bends, the rocker bends, etc. Valve spring forces are only part of the load.

 

If you have a weak valve spring due to wear and use. I pulled my old springs off my heads the other day and some were down to 65lbs of pressure at 1.800"

At WOT, I have aprox 80lbs of oil pressure. Yes, I need to multiply the 70lbs of seat pressure by 1.7 which = which is 110.5lbs. If the surface of the lifter plunger is more than 1 square inch, I might be getting very close to the resisting force of the plunger over coming the spring.

Wee how the oil pressure could play a role with a weak spring?



If the valve is closed, the only pressure the valve spring is putting force on is the retainer and the valve seat in the head. That is why I say the push rod at that point is only seeing the force of the plunger/oil pressure.. It sees equal pressure but the driving force is only the plunger/oil pressure.

Slow down on the reading..







Actually, I refined that and stated we would only need to know spring presure and lifter plunger/pressure. All the spring force is going to be put through the tip of the valve.

 

You obviously still have not grasped the point of preload and the effect it
has on loading the lifter seat. Your above statement is incorrect.

When there is preload...there is a LOAD.

Therefore the pushrod is NOT only seeing oil pressure forces.

Right...

I think this topic has been beat to death and on the verge of getting locked.

 

So explain to me how the push rod is seeing a force greater than the oil pressure force against the plunger if the lifter is on the base circle and the valve is fully seated againt the valve seat.

By the way, I did a little math for you while I was sitting in a class tonight..

65lbs (on the seat) * 1.7 (Rocker ratio) = 110.5lbs on the push rod side of the rocker
110.5/80 (oil pressure) = 1.38125
There would need to be more than 1.38125" of surface area of the lifter plunger for 80lbs of oil pressure to over come the spring force.

A .842" diameter lifter has a surface area of .55682 square inches. Obviously the plunger has less surface area than that as it needs to reside in the body. But with that diameter it would take apox 199lbs of oil pressure to overcome even a weak 75lbs of valve seat pressure. I have no issue admiting when I'm wrong. The likelihood of lifting a valve on oil pressure is probably impossible when actually crunching numbers.

However I do still see some weight in bleed down causing reduction in gross valve lift (as well as push rod deflection ect). On top of that, I still think that it might be possible to slow this degradation process by putting more preload in the lifter allowing you to maintain the volume needed in the lifter easier.

I also can see the possibility of the plunger depth dropping durring rpm bleed down causing the filling hole to miss align and further slow the bleed down process.

I do agree you could run a danger if you start lofting the lifter off the cam lobe, causing a pump up issue.


I don't agrue just to argue. I do it because we all can learn things. Looking at other peoples theoreys sometimes allows us to think outside the box. Until that idea is either proved or disproved, it is still plausable.