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Discussion Starter #1
Well, I guess in general. I'm having this mild disagreement with Steve83 (you may have heard of him). I need some kind of pointer to technical information about how hydraulic lifters work. My idea is basically this:

* They're used to take of lash between the cam lobe and the rocker arm, in order to maintain zero space between the components, and provide lubrication and cooling.

* When they're at the bottom of the cam lobe, the lifter cutouts expose the lifter's filling hole to ~45PSI oil, which "pumps them up". The oil goes into the lifter, and up through the top, through a measured hole that leads up through the pushrod, and down through a 1-way check valve to under a small internal piston that pushes the piston up as far as it can go. This pushing action is also helped along by an internal spring.

* When they're not at the bottom of the cam lobe, but not being back-pressed by the intake or exhaust's valve spring, they retain their pumped-up-ness.

* when they reach the top of their travel on the cam lobe, the valve spring presses back at a very high PSI and this (here is where I am unclear) may or may not squeeze some of the oil out of the lifter at it's pre-defined "bleed down rate". I don't know how fast this bleed down rate is, and cannot figure out if you leave the crank at a spot where the cam is on a lobe, will this eventually bleed down the lifter all the way? How long should this take?

* Does the oil EVER get out of the bottom chamber underneath the internal piston? it's a one-way check valve. Is it simply the clearance between the internal piston and the sides of the lifter body that determines bleed-down?

* If the rockers are non-adjustable, and you hear a lot of clatter, your pushrods are probably too short or too long. But I don't know how to determine what the right length SHOULD be.

For example, my valve train clatters like hell. I have a 96 351W with a rollercam and non-adjustable rockers. My pushrods are RP3278's, which are 7.567" in length. When I adjust them so they have zero lash at the bottom of the cam lobe, I can tighten the bolt about another 1/4 to 1/2" before the bolt is totally snug. Sound reasonable?
 

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Discussion Starter #2
How DO hydraulic lifters work, not TO.

Another question: How much side-to-side play should a rocker have on its pedestal? My rockers have a LOT. Like 1/8 or 1/16" of an inch. It's ridiculous. Is it supposed to be smaller?! Would this cause noise? I'm assuming NOT, if the pushrod is centered across from where it presses on the valve.
 

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I know of Steve83, From Memphis if I remember correctly.

When I adjust them so they have zero lash at the bottom of the cam lobe, I can tighten the bolt about another 1/4 to 1/2" before the bolt is totally snug. Sound reasonable?
That sounds reasonable. The extra 1/4 to 1/2 is your lifter pre-load. And you need that extra 1/2 turn after you reach zero valve lash or you'll rattle like crazy.

Another question: How much side-to-side play should a rocker have on its pedestal? My rockers have a LOT. Like 1/8 or 1/16" of an inch. It's ridiculous. Is it supposed to be smaller?! Would this cause noise? I'm assuming NOT, if the pushrod is centered across from where it presses on the valve.
My opinion that is normal. On the cylinders where the valve is closed that is.



As far as how a lifter works? Here's a article that I found.

Closing up the gap between the tip of the rocker arm and the top of the valve stem reduces the pounding effect that can accelerate valve and rocker wear. Because of this, most of the push rod engines that have been built for the last 60 years have come factory-equipped with hydraulic camshafts and lifters. On newer overhead cam engines, hydraulic cam followers serve essentially the same purpose.

The basic operating principle behind hydraulic camshafts is truly old school technology. In 1910, a French car builder near Le Mans, France named Amedee Bollee invented the first self-adjusting valve tappets. Bollee’s two-piece tappets consisted of an upper and lower piston held slightly apart by a small spring. A port in the side of the lifter bore allowed oil to enter the cavity between the two pistons.

Oil pressure pushed the upper piston up to remove slack between the tappet and valve (this was a flathead engine where the tappets push up directly against the inverted valves). There was no danger of oil pressure pushing the valve open because the pressure exerted by the valve spring holding the valve shut was far greater than the oil pressure inside the tappet.

When the cam lobe raised the tappet, a one-way ball valve in the oil port prevented the oil between the pistons from leaking out. The oil trapped between the two pistons was incompressible, so the tappet acted like a solid member to push the valve open.

In the 1930s, General Motors developed its own “zero lash” tappets for some of its engines. By the 1950s, hydraulic lifters were common in most engines and are still used today.


Inside a Hydraulic Lifter

In a modern hydraulic lifter, a hardened steel push rod cup sits on top of a plunger mounted inside the hollow lifter body. A lock ring in the top of the lifter holds the assembly together. Under the plunger is a spring that holds the plunger up so oil can fill the cavity between the plunger and lifter body. A one-way check valve in the bottom of the plunger allows oil to enter the plunger cavity but traps the oil inside when the lifter moves up. This prevents the lifter from collapsing, which would not allow it to open the valve fully.

The clearance between the plunger and lifter body is extremely tight, typically 0.0002? or less. This is done to limit oil loss from inside the lifter (called the “bleed down” rate) when the valve opens and closes. A small amount of leakage (bleed down) must be allowed with each valve cycle so the lifter can readjust itself to maintain zero valve lash.

Valvetrain clearances change with temperature as the engine heats up and cools down, so the hydraulic lifters have to constantly compensate for thermal expansion in the block, heads, pushrods, valves and other valvetrain components. If this were not done, the lifters might retain too much oil, pump up and overextend themselves, preventing the valves from fully closing. This, in turn, can cause valve float, a loss of compression, misfire, and possible valve damage if a valve remains open long enough to hit a piston.
Features and Limitations

The very feature that allows hydraulic lifters to self-adjust and maintain zero lash can also work against the lifters at higher engine speeds. As engine rpm increases, the bleed down rate inside the lifters may be too great. There may not be enough time to refill with oil between each valve cycle, causing the lifter to collapse. Or, if the bleed down rate is too low and the lifters retain too much oil, they can pump up and overextend the valves. Either way, you can end up with valve float, misfiring and loss of power.

The rev limit for a typical set of stock hydraulic lifters is usually around 6,200 to 6,500 rpm. If you want to rev the engine higher than this, you either need solid lifters or modified performance lifters that can safely handle higher rpms without pumping up or collapsing.

The bleed-down rate of a hydraulic lifter can be varied by changing the internal clearances between the plunger and lifter body for other reasons too. Some aftermarket hydraulic lifters designed for street use have a higher bleed down rate that effectively reduces camshaft duration by 6 to 10 degrees and valve lift .020 to .030? at low rpm for increased intake vacuum and throttle response. At higher rpms, the higher bleed down rate has less of an effect allowing normal camshaft duration and lift.

Hydraulic lifters that have an “anti-pump up” design are made with tighter internal clearances and/or special valving to reduce bleed down. Anti-pump up lifters allow higher engine speeds and are a good choice for a dual-purpose street/strip engine. One supplier of such lifters says their anti-pump up lifters can handle engine speeds up to 7,500 rpm with no valve float, and can even be used with many camshafts that are designed for solid lifters.

from Hydraulic Camshafts and Lifters 101
 

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Discussion Starter #4
"Oil pressure pushed the upper piston up to remove slack between the tappet and valve (this was a flathead engine where the tappets push up directly against the inverted valves). There was no danger of oil pressure pushing the valve open because the pressure exerted by the valve spring holding the valve shut was far greater than the oil pressure inside the tappet."

This paragraph is misleading. The oil pressure isn't constantly applied, and if it was a battle between the valve spring PSI and the oil pressure PSI, of course the valve would win, but that's not how the tappets are made any longer.

the problem is that there isn't constant oil pressure applied to the tappet (lifter), it's only when the tappet is at the bottom of it's bore. It gets filled at 45 PSI through a one-way check valve, rises *all the way*, then the tappet rises and starts to close the valve spring, which should "push back" on the filled tappet and *here I am unclear* compress it. But compress it how fast? what should the bleed down rate be?

Plus, if the tappet is filled all the way and is stiff as rock, what sense is it putting preload on the tappet, wouldn't this cause the valve to be slightly pushed out?

What I'm saying here is that I think it takes much more pressure on my tappets to get them to bleed out than my valve springs apply. It's "as if" I have "anti-pump up" lifters. I would call them "anti pump down" lifters.

I think when you have these very slow bleed down lifters, it becomes very, very important to have exactly the right push-rod length.

I'm still looking for somebody to spell out how to determine the correct push rod length for a non-adjustable rocker. I'm thinking you get the cam on the base ring, get an adjustable push rod and fit it into the slot, and adjust it until it just gets snug, and then add 0.050" to it for lifter preload. Is it that simple?
 

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Maybe. Because of the many variables in head, cam, rockers, etc., lengths may change. There are several makers of push rod checkers, and if you've changed anything from stock, you really should make sure your rod is the proper length. Comp Cams has a fairly good explanation on how to figure if you're correct. One thing that I've found out when modifying, throw any number you thought was set in stone out the window. You measure for the relationship in your components, not how it came out from the factory.

http://www.compcams.com/Technical/Instructions/Files/Verifying Pushrod Length And Rocker Arm Geometry.pdf
 

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Discussion Starter #6
what I figured out is that you need to measure them "the normal way", get the right measurement, stick them in, and if they don't work right (clacky), then something else not the pushrod length, is the problem. What I didn't understand is that oil viscosity and temperature make all the difference in tappet performance. When the oil is hot, the tappet acts like a whole different beast. When it's COLD, you get almost no bleed-down. it's all designed to work at a specific operating temperature and viscosity. The oil fill and bleed holes and wall thicknesses take this into account.
 

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Have you researched what difference , if any it makes with using Synthetic Motor Oil ,Synthetic Blend Motor Oil,High-Mileage Motor Oil and Conventional Motor Oil ?
 

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Discussion Starter #8
From what I understand, all the different oil types are supposed to work "about the same" for a given viscosity rating. but you never, ever want to put synthetic oil in a dirty old 150K+ engine after running conventional oil the whole time, because the synthetic stuff breaks down deposits and makes them free-floating and those deposits will gum up your tappet's one-way check valves and then you need to buy new - well, everything. if you must, go with a blend.

synthetic oil doesn't "flow more freely", it has "more consistent sized particles" in it, which results in it flowing more freely, but at consistently the same viscosity. In other words, conventional oil has a wider range of chains of molecules in it, and the longer chains of particles (oil) are more likely to form clumps and deposits. In your tappets.
 

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Seen a lot of difference of opinions on " because the synthetic stuff breaks down deposits " for example

Synthetic lubricants produce sludge.

Untrue. In point of fact, synthetic motor oils are more sludge resistant than their petroleum counterparts, resisting the effects of high temperature and oxidation. In the presence of high temperatures, two things can happen. First, an oil's lighter ingredients boil off, making the oil thicker. Second, many of the complex chemicals found naturally in petroleum base stocks begin to react with each other, forming sludge, gum and varnish. One result is a loss of fluidity at low temperatures, slowing the timely flow of oil to the engine for vital component protection.

Further negative effects of thickened oil include the restriction of oil flow into critical areas, greater wear and loss of fuel economy.

Because of their higher flash points, and their ability to withstand evaporation loss and oxidation, synthetics are much more resistant to sludge development.

Two other causes of sludge -- ingested dirt and water dilution -- can be a problem in any kind of oil, whether petroleum or synthetic. These are problems with the air filtration system and the cooling system respectively, not the oil.
 

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I'm not saying it creates sludge all by itself, or over time, I'm saying if you switch to synthetic after running regular for a long time, synthetic will break up your existing sludge like busting up blood clots, and it will destroy your seals. I've had it happen! I guess some techs told me once that synthetic oil, in addition to containing, well, OIL, also contain sludge-breakup-compounds that prevent sludge from forming. Great if you run it from the start in an engine, not so hot if your engine already has sludge in it.

or so I heard.
 

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In the past, warnings were given about switching to synthetic oil because it could harm the engine. The reason for this was that many synthetic oils contained esters, which are organic compounds mixed with alcohol. This combination was often hard on seals in the engine, and would cause them to wear down and start to leak rather than sludge damaging the seals .Synthetic oil technology has improved over the years, and most cars on the road today should be able to use either synthetic or regular oil, so long as the proper weight is used.

"Synthetic motor oils damage seals. "

Untrue. It would be foolhardy for lubricant manufacturers to build a product that is incompatible with seals. The composition of seals presents problems that both petroleum oils and synthetics must overcome. Made from elastomers, seals are inherently difficult to standardize.

Ultimately it is the additive mix in oil that counts. Additives to control seal swell, shrinkage and hardening are required, whether it be a synthetic or petroleum product that is being produced.

That is from Ed Newman , Marketing Manager for AMSOIL INC., manufacturer of the original synthetic motor oil for automotive applications. He has published more than 200 articles as a freelance writer on a wide range of important topics.
 

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Um, okay. I had a 1997 Explorer w/ 150K miles on it. Changed the oil regularly. As soon as I switched to synthetic (100%), within 6 months, it had sprung oil leaks from the front, rear, oil pan, and head gasket leaks. It was like a sieve. I got rid of it because of it. Whatever the case about synthetic oil & sludge, I would never switch from one to the other on a high mileage engine again. I started off my new Subaru w/ synthetic and will keep it that way.
 

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We seem to be getting off original post a little .I thought the different oils may have been a topic you had investigated in your research into your problem and had data / figures on the subject which MIGHT have been an interest to some members .
 

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Two kinds of sludge, both low temperature and high. Synthetic oil prevents high. Water temp above 195 prevents low, and modern PCMs controlling engines at slightly above 212 degrees to boil out water get rid of the main ingredient needed to make sludge acids. I use conventional non-syn oils now at 9K OCIs and still cannot make my engines sludge up and at over 200K now.

The OP is rattling because the last 1/8th to 1/4 turn is not real, it's interference at running out of thread and why he is rattling. To get it right the lifter top needs to be about .010" deep into the lifter body, the lifters commonly have from .060"-.080" total travel in them and if running like normal you seek to the middle of that. Running the lifter out at .010" has it act like an anti-pumpup type, we used to run normal cheap lifters like that and at 7500 and plus sometimes rpm with no pump up at all. The spring being stout enough to allow zero valve float is what stops the pump up, it can only happen when parts separate at float.

I used to use a C-clamp to collapse oil filled lifters by hand all day long.

You can spring oil leaks everywhere if the PCV valve stops up really good.

The rockers having that much side flop are not at zero clearance, the flopping disappears once that tight. Unless using ball type rocker pivots.
 
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