(1)what is the usual amount of preload, in inches of distance, on a stock lifter in an LS1? I've read at cranecams and compcams that they say lifter preload should range in the neighborhood of 0.020" to 0.060" inch but I thought I saw some numbers stating otherwise for the LS1. I have limited experience but I imagine there's different sizes and dimensions of lifters so preload ranges can vary a bit?

a typical lifter new out of the box dry, has it's internal plunger pushed upwards against the retaining lock by an internal spring. When you install it and tighten down on a rocker arm, it pushes down on the pushrod and depresses the plunger in the lifter, and how far it depresses the plunger is called preload correct?

So, when the engine is running...

(2) and the valve is closed by the valve spring and the cam lobe is no where near the lifter, the plunger will still be depressed by roughly the same amount of preload when it was first adjusted, temperature differences and wear not withstanding?

(3) and the rotating cam lobe is pushing up on the lifter, which in turn on the pushrod to the rocker to open the valve against 200+ lbs of valve spring pressure, what keeps the plunger in the lifter from bottoming out? Is it oil in the lifter, because the oil (liquid) is incompressible? What keeps the oil in there, a one way check valve that lets oil in but not out?

(4) what is the definition of lifter pump up? Is it oil, pressurized by the oil pump and forced into the lifter, being strong enough to push up on the plunger, and in turn against the pushrod + rocker to overcome the valve spring when the valve is open at or near max lift? How about when valve is closed, preventing the valve from fully seating? Or, is just having pressurized oil is in the lifter mean it is pumped up? Is the term "pump up" regarding lifters good or bad?

(5) what is the definition of lifter bleed rate? Is it simply how fast pressurized oil in it escapes, so the oil in the lifter underneath the plunger no longer has enough pressure to push the plunger upwards against the pushrod?

(6) Does the amount of lifter preload affect valve timing, and engine performance? If you have a lifter, new out of the box dry, and it's plunger depresses and bottoms out at 0.100" so a preload range of 0.020" to 0.060" seems to make sense, would setting preload at 0.020" vs. 0.040" vs. 0.060" have any affect on engine performance in any way? If so, why?

(7) if you have a certain preload range you're shooting for, what are the reasons you would, or would not, want to shoot for the low end (0.020") and the high end (0.060") of the preload range ?

6 and 7 are what i'm most interested in, I had a 4 cylinder gm boat motor I was tuning, it was flat tappet lifters and adjustable rockers. Book called for 3/4 turn on the rocker nut after zero lash. I've heard do less for better high end performance, so I had tried 1/4 turn and 1/2 turn and at 4500 - 5000 rpms I would get a backfire/pop once every 5 or so seconds. Running at any other rpms was fine, finally readjusted the rockers to 3/4 turn and no more popping at high rpm. I'm trying to understand what was actually happening, along with verify my understanding of hydraulic lifters. The rocker studs were 28 threads per inch I think, and the rocker ratio is 1.75 according to the book. Not sure on the math, for 28tpi 1 turn of the nut = 0.0357" distance downward, is that the same distance the lifter plunger is pushed downward or does rocker ratio factor into it somehow?

 

I have Crane rockers so I can adjust each valve on at a time. I put a dial indicator on the rocker at the pushrod end, adjust the rocker to zero lash, zero the indicator, then adjust the rocker for .060 preload seeing how many turns it takes. Im my case it was 1 and 1/2 turns. So I adjusted the rest 1 and 1/2 turns. With stock rockers I think you will have to get the correct preload with an adjustable pushrod and then buy the correct length pushrods.

 

Exactly the way I set my comp cams roller rockers.. .060 here as well...

 

what i can't get my head around is how the lifter can support the valvespring at full compression but 'gives' up the preload distance when the spring is at install height.

i would think if the XX psi oil pressure in the lifter can support 200++ # of compressed valve spring then it would also compress the valve spring some amount when there was a preload.

subscribing

 

Who says the lifter is at the top of its travel on the nose ofthe cam. Me thinks its preload, depresses slightly on frist takeup of the ramp, over the nose might lose a bit of that measured preload and gain from base circle lifter travel, and then on the setdown of the lobe likely sets a little deeper in the lifter body. The snap rings most lifters had would break if there a real force on them, as in - enough force to overcome a 400 lb spring pressure while your running up a cam lobe

 

Ok, bud. Real simple

You have a lifter bore that the tappet registers in right? that bore has an oil passage drilled 90 degrees to it's axis that sees a constant supply of oil under pressure.

Look at your lifter closely. Notice a feature machined around its circumference? That groove does a few things. It allows oil to transfer to the rest of the galleys when in the down postion riding along the base circle of the camshaft. It also lubricates the lifter bore 360 degrees. Within this groove there are also a couple holes drilled that open a passage to the lifter's inner spring cup and the plunger that the pushrod locates on.

When the cam is on the base circle the lifter sees hydraulic pressure and the cavity is filled. The excess is shot up the pushrod and it lubricates the top end. When the cam begins to open the valve the lifter moves up and the oil supply is cut off from the engine. It is now trapped in this cavity. As you eluded, a fluid won't compress (much) and this is how the lifter overcomes the tremendous spring pressures without flattening out like a pop can being stomped on.

You must remember something. 200lbs on the seat does not mean 200lbs on the lifter. It's more than that. Take a stock LS1 with a 1.7:1 ratio. The ratio works backwards and you end up with 340lbs of pressure on the lifter when it is in a closed state. The spring has mechanical advantage over the pushrod and lifter. It's a pretty linear change when opening. It progressively increases the more you open the valve. I imagine the new behive springs might deviate from this a bit as their rate must certainly change due to the diameter differences between the top and bottom of the spring.

Now we can see why pushrods and lifters need to be well made.

The lifter completes the valve event and then closes. Oil pressure resumes and what ever is lost by leaking or squirting up the pushrod is replaced.

This is why they run so quiet. Everything sees continual hydraulic pressure and runs in a zero lash state.

Solid lifters are more accurate though. It is a true 1 to 1 mechanical relationship. this means more accurate valve timing and more noise as a consequence.

I imagine knock sensors don't care for this much.

Hydraulic lifters are limited a bit in RPM as well. Not likely to expect much from a 9K rpm engine with a hydraulic camshaft I doubt the lifter would have time to "recharge" between cycles at that speed.

9K means 4500 rpm on the cam. A four stroke fires every 4th rotation right? We have intake, compression, power, and exhaust. Divide 4500 by 4 and it means that there are 1125 power strokes every minute. Divide 1125 power strokes by 60 seconds and you have The intake valve and exhaust valve cycling almost 19 times a second. The oil pump would have to be able to fill all 16 lifters 19 times a second. A daunting task.

Imagine that in your head.

That's moving right along.

It fascinates me that these things work as well as they do. let alone go for hundreds of thousands of miles.

Hope this helped a little.

 

the lifter being sealed off to support the spring makes a lot of sense until you consider that captured oil still has the opportunity to shoot out of the pushrod... correct or no?

 

You a smart man. I was hoping that question would be asked.

The simple answer is, nothing. The hole is "metered" meaning it is a diameter designed to allow some fluid to pass without affecting the overall lift that the valve sees.

I snooped through the internet searching for a more "educated" answer and came up short, so my response is nothing more than a consortium between myself and my colleague sitting ten feet away from me.

I'm going to sound like I'm back tracking now, but if anyone has additional input on exactly how that portion of the lifter's function operates, I'd like to know too.

Hope this helped.

 

you're question is exactly what I want to know too,

what i'm looking to understand is how, or if, different preload amounts on a lifter has any affect on how they operate, and why.
I appreciate the replies but I really don't want to hear I preloaded my abc lifters to 1.5 turns or 0.080" and everything runs good. that's not what i'm asking.

I know in general that hyd. lifters are valved and they either prevent/trap oil within themselves or allow a certain amount to escape out (bleed rate). But I want to know how these things happen and what affects their operation which then translates to an affect on the opening/closing of the valve. Very detailed pics or cad drawings would be a start, what's available on the web now sucks. I will probably go waste $5 on a lifter to pull one apart i think.

 

I don't have a CAD drawing but I think I can explain this. A Hyd roller lifter is made up of 5 pieces. The housing, the spring, the plunger, the pushrod boss and the retaining wire.

For this to make sense I and going to describe the way it would come apart, what each part looks like, then I'll go back together with it and explain how it works. It's the only way I can think to do this without pictures.

So you remove the retaining wire, the first piece to come out is the pushrod boss. This is what the pushrod sits in. It's .475 thick or tall, it has four small grooves cut in the bottom and a hole in the side. The hole goes to a hallow area; this area is just below the pushrod hole.

The second piece to come out is the plunger, over all it's about 1.00 tall, it is completely hallow no top on it, like a cup and at the top has a smaller outside diameter about .200 tall. In the bottom of the cup is a one-way check valve (ball).

Below this is the spring, the spring is what you feel when you preload the lifter.

Ok, the small hole you see in the side of the lifter body feeds oil into the lifter. This hole fills a small oil galley inside the lifter body; this oil galley is made up of a machined area inside the lifter body and the reduced O.D. of the top of the plunger "cup". The pushrod boss sits on top of the plunger, like a lid, the oil goes into the "cup" from the small oil galley in the lifter body. The oil passes between the lifter boss and the plunger through the small-machined grooves in the bottom of the pushrod boss. The oil fills the cup then passes through the check valve at the bottom of the cup to the bottom of the lifter body. It also goes up into the pushrod boss, the oil passes between the outside of the pushrod boss and the inside of the lifter body through the small hole and into the chamber where it can go up through the pushrod. This happens only when the lifter is in the oil galley and sees oil pressure. As the lifter comes out of the oil galley and the pushrod pushes back down on the plunger the check ball traps the oil in the bottom of the lifter. The plunger rides on the trapped oil under it. The small hole that you can see on the outside of the lifter has nothing to do with trapping the oil in the lifter. The oil is trapped under the cup. (The cup itself can be empty) This is what pushes the pushrod up; a fluid is not compressible. Once the lifter comes back down into the oil galley it sees pressure again and fills the middle chamber, pushes oil through the check valve if it can and sends the rest up through the pushrod, as the lifter comes out again it sees no pressure the valve spring pushes back on the pushrod which pushes on the plunger which closes the check valve and opens the intake or exhaust valves.

The more you preload the lifter the more lift you lose at the valve. Because you are making the chamber under the plunger smaller which won't fill up with as much oil. When the chamber fills there is no pressure on the plunger just the spring holding the plunger up. The further you push the plunger down with preload the smaller your making this chamber. You are making your lifter shorter and will lose valve lift. I set all my hyd lifter motors with as little preload as possible.
This is why a solid lifter is much better for HP, one it's lighter, it doesn't need to fill up with oil, two you lose no lift, and three you can run big spring pressures without killing the lifter.

Any questions LOL...

 

Good information, thanks for that. You say you set your preload as little as possible, but what is the limit?

 

For someone claiming to be reasonably knowledgeable on the 4-stroke combustion engine, this sure is a comically fundamental misunderstanding. Try 2 revolutions for every power stroke in a 4-stroke engine: http://auto.howstuffworks.com/engine1.htm

 

thanks very much for the replies.

but,

coming back to one of my main questions, how can any amount of preload have any different affect on the opening or closing, or duration and anything else, of a valve?
Because the fact there is a check valve in the lifter, so when the cam lobe begins to push the lifter upward oil is trapped within the lifter. The oil is incompressible. So why would having more or less oil in the lifter make any difference?

And as for losing valve lift with having more preload, again shouldn't it not matter because of what I just said? Provided the lifter operates properly (the check valve doesn't leak) and the lifter is full of oil [regardless of whatever the internal volume the lifter might be due to preload] it's going to act like a solid lifter. The lobe lift does not change, the rocker ratio doesn't change, so the valve lift should not change. no?

 

The nose of the rocker does not sit on the valve stem in the same place.Therefore you lose lift which is why pushrods are required to be the right length also.

 

ok, not so much the rocker tip sitting in the same place, but i would agree that if you change the axis location the rocker rotates about, caused by some length change of the pushrod mechanism, that it has an affect on rocker arcing which will effect maximum valve lift... the mid-lift principle,
Can someone do the math?

but in the practical sense for what I'm asking is it significant?
I don't think it is. If it was, then all the people who are deviating from the 3/4 turn down from zero lash oem preload to 1/4 turn gotta be upsetting their valvetrain geometry- that's then saying the oem has the valvetrain geometry correct in the first place but then how could going less preload gain better performance like everyone claims? It cannot be due to increased valve lift, cause if you deviate anywhere from a 90 deg angle from pushrod to rocker fulcrum axis at mid cam lobe lift, mathematically you will end up having less than maximum lift on the other end at the valve (because of less radial motion of the rocker).

but going back to my original question, i was asking what is the affect on the valve/valvetrain and affect on performance by going any given amount of preload on the lifter, primarily the statement you always hear less to zero preload makes it act like a solid lifter = better performance, typically higher rpm. Still, I don't understand how or why a lifter would act any different for any given amount of preload.

And at the moment I don't believe it's due to any increase in valve lift, meaning the lesser preload just so happens to make the valvetrain geometry more correct. I guess it would be a 50/50 chance, but I need to see numbers, math, and logic first but right now that's the only logical thing I can think of that would have any affect.

http://www.mid-lift.com/TECH/TECH-ML-ARC.htm

 

4500 power strokes

 

times 8

 

And 17 years later, here you are with non-answers....