ChucksZ06

iTrader: (9)

Does anyone know how much a hydraulic lifter compresses (if any) as it takes up the pressure in opening the valve spring? ( when the engine is running and the oil has pressurized the lifter) I would think the pressure of the spring would have something to do with it? Any suggestions appreciated.

GuitsBoy

iTrader: (4)

Oil is non comprressible. In theory, the lifter would not compress at all unless there's some air trapped in there or disolved in the oil, but even then it should be imperceptible.

777

iTrader: (21)

This may sound newbish, but then what's the point of a hydraulic lifter if it acts as a solid lifter?

GuitsBoy

iTrader: (4)

Dont you mods know anything?!?

As the oil fills the lifter up, it takes up any free slack in the valvetrain. Think of hydraulic lifters as automatic lash setting lifters. Too much valve spring pressure can push the oil right out of the lifter and collapse it.

777

iTrader: (21)

Ok, that's what I was thinking, but the way you said it got me confused. But actually we know nothing. We are brainwashed of everything as soon as we become mods. Then we have to search for all of the information. Since search is broke I've been struggling It's just so Brian, Tony, and John can laugh at us.

MadBill

There is another thread floating around that gets into great detail re lifter collapse due to air in the oil, and sometimes because of lifter body distortion...

GuitsBoy

iTrader: (4)

Yeah, this whole search thing is bumming out a lot of people. Infact I dont think JRP has posted at all in the last couple months

GuitsBoy

iTrader: (4)

I would assume thats why the encapsulated version is perferred? Keeps the lifter body distortion to a minimum and hopefully the oil cant seep past the plunger when under heavy spring pressure?

ChucksZ06

iTrader: (9)

Thanks...you guys sort of answered my question. I think I would argue that it compresses a little bit...say ... .005 to .010. I guess i should rig up an oil pump to provide 60 psi to the engine, turn it over manually and measure the deflection if any. I appreciate the thoughts.

GuitsBoy

iTrader: (4)

It may well compress, but keep in mind that if it does, there is air in the oil since oil is an uncompressible liquid.

777

iTrader: (21)

cyphur

iTrader: (10)

Post *****

Search being down sucks. Good thread tho.

vettenuts

iTrader: (4)

Well, its not "fully" incompressible. You will also get distortion of the lifter as well as the pushrod, with the pushrod likely being the biggest contributor to lift reduction. I also wouldn't count on a static roll the motor over test, the dynamics involved are going to change loading on the lifter dramatically.

GuitsBoy

iTrader: (4)

Everything ive ever heard or read says oil (or any liquid) can not be compressed at all. Perhaps the elastomers which give it the lower "W" rating can be compressed in the oil?

ChucksZ06

iTrader: (9)

I know what you are saying about a liquid not being able to be compressed but there is a pushback happening from the spring pressure. When the lifter starts opening the valve (say a 100lbs on the seat + the rocker ratio) and then continues to open the valve to say 320 lbs the pushback on the oil in the lifter increases dramitically and the oil pressure is a constant in the engine. I understand the hydraulics involved but It seems there must be a small deflection of the lifter? If the lifter were used with a 600 lb spring it would deflect or collapse right?

GuitsBoy

iTrader: (4)

I believe this is caused by the oil seeping out of the lifter.

bowtieman81

iTrader: (35)

All you guy are basically correct. Oil (and water) is engineering wise considered incompressible, assuming no air vapor is present. In reality those liquids will compress a very tiny amount, which is considered negligible in engineering calculations. Hell, even air is considred incompressible up to mach 0.9 or so.

Bottom line is with the tiny amount of oil in a lifter and the tiny amount it will compress you aren't going to be able to measure any differnce based solely on oil compressing. Now, if you have air trapped in there that's a different game.

Also, if the pressure on the oil got high enough it could deflect the lifter itself. It would have to get pretty high though, typical hydraulic systems run at 3000-4000 psi, occasianally more. I would guess you would need valvespring pressures more than 1000 lbs to see lifter deflection (educated specualtion there).

954RR

iTrader: (1)

Physics and Fluid Dynamics 101

Also like said above it would take considerable pressure to accomplish the task of compression but, a consequence of compressing a fluid is that the viscosity, that is the resistance of the fluid to flow, also increases as the density increases. This is because the atoms are forced closer together, and thus cannot slip by each other as easily as they can when the fluid is at atmospheric pressure.

I don't think that this would be a problem in an ls1.

cowboysfan

here is my theory. solid lifters are hard on valve train during idle, plus dont pump up oil into the heads as much as hyd. lifters do. hyd. lifters at idle pump up more oil to heads due to the pumping action of lifters during idle. oil keeps metal cool. the more the better! right? now at high rpm's the hyd lifter does not have time to compress much compared to engine at idle,but even at high rpm's hyd lifters do have some pump action which will provide more oil then a solid lifter. so you wont get full lift at high rpm's w/ hyd lftr. as compared to solid lifters.with this all said, oil viscosity and aeration in oil has affect on this as well .

so you ask how much does hyd lifters compress, would depend on how oil aeration affects the brand of oil u r using, spring pressure that takes to compress, rpm's and cam lift.
I'm sure there is more to this , but I;m trying to keep it simple.
hope this helps some.

fuerzaws6

vettenuts

iTrader: (4)

Oil pressure internal to the lifter is higher than the engine oil pressure since it is trapped under the piston. As the pressure increases, don't forget you are holding it in an elastic chamber, in other words the lifter itself will expand some very small amount. We see this all the time when we dynamically load hydraulic actuators and power cylinders at work although the chamber volume in which the compressed oil resides is much larger.

For valvetrain deflection, I think you are fishing in the wrong pond. In the end these are going to be smaller numbers in comparison to other valve train phenomina that are taking place like pushrod deflection, rocker deflection, etc. as the valve is opened and to observe these you have to have the engine dynamics taking place, static deflections are going to tell the whole story.