Head or Valve Train Geometry

[Flash]

I'm not too much in to the science of it all, more the mechanical part of it. it's important, of you modifying, to understand what you are changing and why or what it will affect. Even installing a bigger cam shaft in to a stock 4.0L will change the way it is designed.
Geometry, is a balance or positioning of parts, so that they work to get the job(all of this is figured out before the first mold is made and a cylinder head is produce) done, with room to spare.(they don't burn up or brake)
Here is a good link that will help you out.

http://www.hi-flow.com/HPYT4.htm

When i get time, i will try and make it a little bit simple for those that don't want to read thru all the info in that link.
For now, read thru the link, as there is good info to be had


Flash

[John]

Very good topic and nice link. This link from Lunati provides a simple check for what you presently have I think it might help some. http://www.holley.com/data/TechService/ ... ometry.pdf Although they talk about using a solid lifter, a pumped up lifter will work.
John

[gradon]

I read 1/4 of it and will finish it later. I qualify for 5 of the 7:
"Areas that can cause clearance problems between valves, block and pistons are…….
*Head or block faces machined excessively--.004" head and .025" block
*Flat top or zero deck piston height or domed pistons--I'll be .0045" below zero deck
*High lift camshafts--P4529230AB [email protected]"(but medium lift compared to some of you)
*Oversize valves--XX thought about it
*Higher rate – stiffer valve springs--Mopar Performance P5249464(recommended for the P4529230AB cam)
*Higher ratio rocker arms--XX would've done these w/ a stock lift cam
*Thinner than standard head gaskets--.043"
The most common causes of interference are encountered when fitting some or all of the above components."
At least we know that our Jeeps didn't have an ideal quench so there is room for improvement.

[Flash]

Very good topic and nice link. This link from Lunati provides a simple check for what you presently have I think it might help some. http://www.holley.com/data/TechService/ ... ometry.pdf Although they talk about using a solid lifter, a pumped up lifter will work.
John

that is exactly what i was looking for

But as i have travel, on my "Internet search"......they all talk about the push rod being the key to keeping the rocker arm on the center of the valve........I'm confused?????????? as long as the push rod is not holding the valve open................the push rod shouldn't change were the rocker arm, to valve stem/tip relation starts......a longer cam can make the travel longer across the valve tip..........But how in the world does a push rod change this..............I CAN see how shimming the rocker arm would affect this..............I JUST DON'T GET IT Some one enlighten me, Please!!!!!!!!

Flash

[John]

Lets take it to the playground, a teeter totter is a good example of a 1 to 1 rocker ratio, our 1 to 6 ratio will make the effects more pronounced.. The pushrod is me, holding the beam (rocker) to the ground. Instead of a valve stem a string with a plumb bob is attached to the opposite end of the beam. Mark where the plumb bob hangs on the ground, Now raise the seat 2 feet. Our plumb bob now marks the at a different place. By raising the pushrod length we move the contact area at the valve stem due to the simple arc. The contact wear area in our real world valve train needs to be centered on our valve stems or we encounter side loading of the valve with its increased heat build up, increased wear to valves, valve guides and possible galling.(that one will wipe a cam lobe). Changes to deck and head height, changed camshaft lift, shimmed rockers quickly change the geometry. When things are golden there is a nice narrow band of operation at the rocker/valve junction that will be centered on the valve stem.
John

[Flash]

Lets take it to the playground, a teeter totter is a good example of a 1 to 1 rocker ratio, our 1 to 6 ratio will make the effects more pronounced.. The pushrod is me, holding the beam (rocker) to the ground. Instead of a valve stem a string with a plumb bob is attached to the opposite end of the beam. Mark where the plumb bob hangs on the ground, Now raise the seat 2 feet. Our plumb bob now marks the at a different place. By raising the pushrod length we move the contact area at the valve stem due to the simple arc. The contact wear area in our real world valve train needs to be centered on our valve stems or we encounter side loading of the valve with its increased heat build up, increased wear to valves, valve guides and possible galling.(that one will wipe a cam lobe). Changes to deck and head height, changed camshaft lift, shimmed rockers quickly change the geometry. When things are golden there is a nice narrow band of operation at the rocker/valve junction that will be centered on the valve stem.
John

Sorry, I still don't get it!

In other motors, this could be different but,(this is how i see it. PLEASE point out were I have gone astray) If you hold "light pressure" on the push rod end, of the rocker arm(this representing the "no lift" side of the cam lobe) this is what the rocker arm(stock factory Geometry) would be(Head shaved or not) the plane, between the pivot point and the valve stem would be the same. if the push rod become longer or shorter the push rod would ride deeper or shallower into the Hydraulic lifter. This is why you need a longer or short push rods(or shim rocker arm pivot up),is that , the lifter can only work properly in a vary short window of the total travel of the Hyd lifter.(talking about the piston travel inside the Hyd lifter its self) the geometry would not change unless the push rod bottom out in the lifter(holding the valve open) or(push rod two short) was loose on top of the Hyd lifter causing the lifter to be loose.
The geometry, or the degrees of a circle between the pivot point and the rocker arm would be unchanged...............If you added a .060 shim under the rocker arm you would change the the Geometry or degrees between the pedestal or pivot an the valve stem...........You would also change the oiling in two ways. (1) you would allow more oil that was puddled in the pivit to drain down the rocker arm and on to the valve stem. (2) you could slow the flow of oil coming out of the small hole in the push rod cup side of the rocker arm.

NOW if we were talking about a old GM 350 with a nut, to adj valve depth in a hyd lifter............Now the push rod height affecting valve tip relation ship make sence to me......

First lets explain the different between the two. 4.0L, has a rocker, pivot ball, stud(bolt in this case), and rocker arm that pivots in it. The, Stud(bolt) is tightened to the head securely and the rocker pivot form there.
GM, Has a rocker arm, pivot ball ,stud/nut, similar to the 4.0L but,..... it's NOT tightened down to the head. the rocker arm is suspended Agnes the pivot By the push rod holding it and pushing up agence the nut, on the stud. The shorter the push rod is, the farther the pivot nut would have to be tightened down to set the proper preload of the Hyd lifter.....Which means that you are raising the pivot point up or down, changing the axis or degrees between the center of the pivot and the valve stem(Like we would do with a shim)

I know I'm NOT Right!...............from what i have read so far..............just can't find any where that show my theory to be Flawed

I even remember reading in my DC( Direct Connection) Eng manual (yeah, i know showing my age ) were they were taking about with a Adj rocker arm, technical, hi lift, it was crucial that you had only...........like one thread showing, two max or you need to select a different push rod length...........Just can figure out why

Going to that book now and re reading that section

Flash

[gradon]

I understand your see-saw example(I was looking for the other common correlation/simile word, but couldn't remember it.) John. Should there be a 90* angle between the the pushrod and rocker@ no lift(see-saw parallel to ground)? And then at .045" lift(30 cam), the angle will be more than it was with the stock cam(see-saw goes a little higher than before--why you don't want to re-use rockers w/ lower-lift wear patterns). I am definitely leaning towards the RRs so I don't have to worry about the side load on the pushrods.

[John]

Preload, lifter pump up, valve float.... We Tighten one bolt (No offense) at the trunion to a set torque to adjust some critical settings, if the pushrod is too long or too short, our adjustment will not set things where we want them during operation. Prefill the lifters, assemble the motor without the rocker arms, put #1 cylinder at top dead center and start assembling the rocker assembly by hand. Tighten the bolt until slack is taken up at the pushrod, rocker seat. Measure the gap between the rocker and the head and it should be .040 - .060 and if not your pushrod is the wrong length. If the correct length. The valve stem,rocker arm will center up pretty well when torqued down and your preload should be right on. Repeat for each cylinder when the cylinder being worked on is at it's top dead center.
Side loads can really cause valve train problems, increased wear to breakage at the worst and at the least, lots of heat in our oil.If you your build considers reliability at least put in new rocker assemblies, eliminate those wear patterns that are in the wrong place and best rollers. If you are truly considering/running a high lift cam it will make even more difference. And dont worry too much about side load on your pushrods, but worry a lot about side loading your valve guides.
John

[Flash]

OK, the search has ended(I think) Reading over this statement, for the 2nt time.........it finally sunk in!

"The contact point will be closer to the centre at zero lift than at full lift if the push rod is too long and vice versa if the push rod is too short. It is important to note when using rigid mount shaft type or pedestal type rockers, the mounting pedestal or spacer height may need to be altered to make geometry changes."

In other works the push rod high is vary important to the lifter preload..............but rocker arm shims or relocating the bolt hole,.... would be the only cause of a change in Geometry of the rocker arm.................Or if a longer valve stem was installed..........
I guess in a sence, the push rod length, still affects geometry do to the fact that in order to us the stock push rod on a decked/shaved combo would require that the same amount that had been shaved of the bottom be added to the pedestal mount and the valve stem would have to be equally longer also...................................................

What say you?

[John]

Enlightenment... Did we just agree? If you have just skimmed the head and block for flatness, you will be likely good enough on pushrod length, If you went for minimum deck on a short rod build, you need shorter pushrods badly, to keep your valve train reliable. If you need to change the geometry, which other component would you rather change?
John

[Flash]

Enlightenment... Did we just agree? If you have just skimmed the head and block for flatness, you will be likely good enough on pushrod length, If you went for minimum deck on a short rod build, you need shorter pushrods badly, to keep your valve train reliable. If you need to change the geometry, which other component would you rather change?
John

Yes!!!!!
Wow, thats the shortis answer i have ever gave........

[oletshot]

Great thread, it's just what the Dr. ordered. I think a lot of people put in the homework for the short block (quench and CR) and kind of ignore the valvetrain, hoping that no mods are necessary (at least I am guilty of this). What is the best way to prefill the lifters? I've heard of soaking them in oil, is this how it's done? I didn't do this because the FSM stated it's not necessary (it stated the oil pump will fill them quickly). I now realize that the manual is refering to reassembling an unchanged stock engine, so checking preload probably isn't necessary (recommended maybe). The only other way I can think right now to prefill lifters would be to install them and prime the pump until the lifters fill. Any suggestions?

[John]

I soak them overnight in a container of oil to prefill, I like to stand them upright with the poppet up. You can depress the plunger with a clean pushrod while the lifters are still submerged to insure they are filled.
John

[seanyb505]

I had a lot of doubts before actually deciding on going with shimmed rocker arms. When I found it would be ok I went ahead and got them but now that everyone is talking about correct geometry its concerning me. I called Hesco and told them my situation, how I would be decking .060 exactly from the block and head total and I had .060 shims. I told them I was concerned about oiling and geometry but they said it was good to go, and that while they did offer shorter pushrods, they wouldnt be necessary. Now either its ok to shim, or they have some really bad salespeople/tech help. But now that Ive thought about it, it would seem that the shorter pushrod can cure both block and head decking, but the shim can only cure head decking without throwing the geometry off. Is this right? Heres my logic: If you take off .010 from the head but shim the rocker arm .010, the relationship between the pushrod, rocker and valve has stayed the same. Now if you take another .010 off the block and shim the rocker another .010 so it is now up to .020, the relationship between the pushrods and rocker stays the same, but the rocker and valve angles have changed. Is this correct?

[Flash]

Yes that is correct,
Hesco said the shim is good becouse..........they sell then!

.060 shim is going to change you geomitry..........I'm guessing here!!!! but, the changed geometry by shimming it will probably shorting the guide life some................

It's to bad you don't have a checking push rod were you could add the .060 shim and see how much it changed the rocker arm to valve stem or tip centering.

If you had a push rod that was adjustable and a old lifter that you could take the cuts out of it(Making it a solid lifter.........You could check it just like on the like that John posted above

http://www.holley.com/data/TechService/ ... geometry.pdf

It would tell you whether you will have a problem or not...............
You can get a checking push rod from most cam places..........Don't know how much they are thow..............Shouldn't be much

Any ways just something to consider.

Flash