Rocker Geometry Measurements

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In your picture, the bottom of the spring is not centered. doesn't that skew the math?

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Be sure the square is resting on top of the rocker shaft and the blade is on the same angle as the valve stem.

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So the tee square doesnt have to be in the bubble, but rather line the edge on the springs? Does this work on all types of heads? Seems the tee square may not work on some? or use the opposit end. Also, cant you just explain the formula after the pic you just posted?

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I would think the bubble would have nothing to do with squaring things up as the head is on an angle on the engine, even on the bench. A better way to measure would be to have the spring off and square it up against the valve stem.

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As always, I am happy to answer questions. I like questions.



Even if I don't like your answers. I didn't realize you were acting as a top secret rocket scientist. I may not be able to say what I see or think, but I can see what needs to be done and do it. It's just math.

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Mike, How about us Magnum guys that are using rocker studs?

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After reading a fair amount about rocker geometry. I settled on the theory that the center line of the rocker arm should be at a 90 degree angle to the valve stem at mid lift. What happens is when there is more valve lift the rocker pivot in relation to the valve tip needs to be moved up. It's simple math to figure it out.
Doug

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Thanks Mike.

Onig

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After reading a fair amount about rocker geometry. I settled on the theory that the center line of the rocker arm should be at a 90 degree angle to the valve stem at mid lift. What happens is when there is more valve lift the rocker pivot in relation to the valve tip needs to be moved up. It's simple math to figure it out.
Doug

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There's a little more to it than that. The valve is not on the same angle as the stand so it must be offset as well. Now how do you accomplish moving the shaft up without major surgery?

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In your picture, the bottom of the spring is not centered. doesn't that skew the math?

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Seriously?????

From the original post:

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Be sure the square is resting on top of the rocker shaft and the blade is on the same angle as the valve stem.

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The picture is a reference to show how to position the square to take the measurement. The spring is an outer from a triple setup that gives a clear view of the square resting against the spring without interference from the retainer. Obviously that spring won't locate on the spring step in the head. Do you really find that troubling or do you just like trying to bust my chops? I'm trying to find ways to help Mopar guys, not tear down others.

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Why all the negativity and name calling. If you disagree with the information just say why and I will figure out the world isn't flat.

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It's the attitude B3RE has taken in his answers. He may well have a good product and it may take care of some valve train issues. I'd try a different approach though .

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Man why do some people always have to question free advice? The guy says "do this" and maybe I can help. And people act like they're making a deal with the devil. How about use a digital level on the valve tip, then use same reading on your square, then measure. Don't be a square about the square doods......

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The basis for the advice is fine by me. I believe wholeheartedly that people should check and correct their rocker arm geometry if needed. The problem I have is when someone claims to help, but only if you call him so he can sell you something. In this case rocker shaft spacers, offset or otherwise. No problem, just place an add instead of misleading people.
Basically just post the formula so people can check their stuff. If there's a problem they can decide how to deal with it.

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Mike, How about us Magnum guys that are using rocker studs?

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The magnum guys have it easy, so to speak. You can correct geometry by altering the pushrod length, but drastic changes get dicey. You need to offset the rocker when large changes are made and that makes studs a real pain in the moon crease. (Or use rockers with a different fulcrum length)

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Checks in the mail - and your expert opinion is:

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In your picture, the bottom of the spring is not centered. doesn't that skew the math?

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Seriously?????

From the original post:

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Be sure the square is resting on top of the rocker shaft and the blade is on the same angle as the valve stem.

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The picture is a reference to show how to position the square to take the measurement. The spring is an outer from a triple setup that gives a clear view of the square resting against the spring without interference from the retainer. Obviously that spring won't locate on the spring step in the head. Do you really find that troubling or do you just like trying to bust my chops? I'm trying to find ways to help Mopar guys, not tear down others.

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Yes, there's a couple of things I find troubling. when you said;

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Be sure the square is resting on top of the rocker shaft and the blade is on the same angle as the valve stem. (See Photo)

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Clearly the square is NOT on the same angle as the valve stem. If it was, the measurement would be different. If you're not careful enough to post a picture that shows things correctly, what other shortcuts will be next?
The other troubling thing is that your post is just a thinly veiled FOR SALE add to get people to call you and buy some kit. If you really wanted to help people you'd just post your formula so people can check to see if they have a problem. If they do, maybe they'll call you. Sorry, but your whole approach looks more like a snake oil salesman tactic as opposed to someone who's really trying to help.

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on the nose

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The head stud is in the way of the valve, but looks like the rocker needs to be raised.

Onig

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Longer pushrods are needed but may cause the rocker to push on the side of the valve stem tip instead of the center, that would require filling the bolt hole and re-drilling it further towards the cam. Or you could offset drill and tap the hole to a bigger size stud

Of course all that makes the PR angle worse than it already is

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on the nose

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The head stud is in the way of the valve, but looks like the rocker needs to be raised.

Onig

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Longer pushrods are needed but may cause the rocker to push on the side of the valve stem tip instead of the center, that would require filling the bolt hole and re-drilling it further towards the cam. Or you could offset drill and tap the hole to a bigger size stud

Of course all that makes the PR angle worse than it already is

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Just measure the width of the sweep pattern, that'll tell you if the geometry is correct. If it's less than .600 lift it should be less than .025 on the sweep. The closer to the center of the valve the sweep is, the better off you are, but it doesn't have to be perfectly in the center to have good geometry.

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Also, is absolute geometry really needed, for most purposes Im going to assume the rocker manufactures have it really close to begin with.

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Really ?!?! You were sounding pretty smart for a while there but you've just dispelled that notion.

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I hear you, but Im referring to the word "Absolute" Im sure many of us dont have it with our rocker arm/shaft/valve combos.

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Like everything else in our hobby, there is rarely an absolute right way. It usually involves a trade-off of some kind. In this case, the trade-off seems to involve centering the roller on the valve tip, which often does not lead to "perfect" valve train geometry. Due to the smaller contact patch with roller tip rockers ( verses scrub type rockers ), I personally am willing to sacrifice "some" geometry to be able to get the largest roller tip contact patch ( middle of valve stem). This also helps in the valve stem wear dept. On the down side I am probably sacrificing some area under the curve.

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We think this post needs to start over and maybe this guy can provide us with more detailed information on how his kits can correct common issues, and after we understand how it works, then he won't have to do a sales pitch, we will be ringing his phone off the hook.
I know it would be of interest to us since we spend so much time on valvetrain corrections and end up with different fixes that are a priority for each build.
I hope he comes back and helps us and himself by educating us on his method and product.

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heck that makes to much sense

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Sorry ,Tony I was think out loud again.I keep my mind/mouth closed from now on.

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Maybe some of you guys should look at that guys kit, it moves the shaft up to correct geometry and back to center the contact patch, the only compromise I see is the PR geometry will get worse, not a big deal on a BB but a SB is already bad. Of course a W2 is worstest yet and they can rev good so

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The CAD drawings I've done say the shaft has to move down to correct geometry with a high lift cam. Moving the shaft up makes things worse on every simulation that I've run.

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Maybe some of you guys should look at that guys kit, it moves the shaft up to correct geometry and back to center the contact patch, the only compromise I see is the PR geometry will get worse, not a big deal on a BB but a SB is already bad. Of course a W2 is worstest yet and they can rev good so

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The CAD drawings I've done say the shaft has to move down to correct geometry with a high lift cam. Moving the shaft up makes things worse on every simulation that I've run.

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FWIW, my Stage VIs required raising the shafts to get the geometry straightened out + lash caps, along w/ test-fitting a variety of rocker arms to come up w/ a combination that actually worked correctly. From what I've heard, that wasn't typical for most Stage VIs, but it's what was required with my particular set.

I think the approach required depends on the application, the particular parts used, and the rocker geometry results (e.g. Jim Miller's Mid-Lift design vs. Jesel's theory) you're looking to achieve.

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I wouldn't hesitate to say these last two posts are over the heads of 95% of the readers of this discussion. Oh yeah wher's my free stuff.

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The concept would be easier to communicate if I took the time to post a picture. Or better yet, a short video would fully explain it in just a few frames.

I first read about the low pivot concept in a GM engine book years ago. The author didn't explain it fully but it sounded interesting. Years later I finally sat down at the CAD terminal and figured it out. The math is too complex for me so I solved the equation graphically. What you're trying to do is to solve the smallest product of load and scrub. When the valve is closed the load is small so you allow a lot of scrub. When the valve is full lift you're at max load so that is when you want zero scrub.

When you solve the equation you end up with the rocker arm perpendicular to the valve stem at about 2/3 of lift. This is below the mid-point theory which is more popular. The mid-lift approach is a simple approach that works pretty well in most applications. But if you're setting up something with 800 or 900 lbs on the nose then you might want to minimize the scrub under load.

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Brad I would like to see an engine with one theory applied on one head and the other theory on the other. Then check the lift at the valve to see which achieves the most lift at the valve. One thing for sure the set up that has the rocker 90 degrees in relation to the valve at mid lift will have the least amount of scrub.

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Mid lift provides the least amount of scrub. Low point (2/3 lift) gives you the least amount of scrub under load. That is, the scrub occurs while the load is low and then when the load is high there is very little scrubbing action.

I think most of the serious valve train designers migrated to the low pivot point design a number of years back. The math is fairly complicated but if you put the rocker arm perpendicular to the valve stem at 2/3 lift you're in the ballpark. The scrub pattern is larger than with the mid-lift design, but the sideways force applied to the valve goes down.

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- try reading the book "Valve Gear design" by Michael Turkish, 1946, Eaton corporation. Turkish was a mathematician who worked for Eaton - and Eaton was a tier one supplier to GM - and probably a lot of other automotive OEM's. Yes, the math is well over my head, but pretty much as you alluded to verses the common 50/50 rocker arm arrangement ( 90* at mid lift) that most use today. My brother ( much smarter than I ) has done extensive research in this area also. I was able to grasp about 75% of what he sent me on the subject. Yes, it is a complicated subject and unfortunately, a lot that has been written about it has been written by people working for magazines trying to sell you a product ( those pretty gold anodized aluminum roller tip rocker arms with your initials stamped on them ). So, since this thread has turned in to "who's the smartest", Could I see a show of hands of those with the title of "Mathematician". - I won't be raising mine .

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Maybe some of you guys should look at that guys kit, it moves the shaft up to correct geometry and back to center the contact patch, the only compromise I see is the PR geometry will get worse, not a big deal on a BB but a SB is already bad. Of course a W2 is worstest yet and they can rev good so

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The CAD drawings I've done say the shaft has to move down to correct geometry with a high lift cam. Moving the shaft up makes things worse on every simulation that I've run.

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Maybe some of you guys should look at that guys kit, it moves the shaft up to correct geometry and back to center the contact patch, the only compromise I see is the PR geometry will get worse, not a big deal on a BB but a SB is already bad. Of course a W2 is worstest yet and they can rev good so

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The CAD drawings I've done say the shaft has to move down to correct geometry with a high lift cam. Moving the shaft up makes things worse on every simulation that I've run.

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If you have a perfect sweep with a .600 lift cam, and then change to a .800 lift cam, the wheel will move closer to the rocker shaft at full lift.
I agree, the shaft needs to go down. I moved my T&D 1.8 sep. shaft setup down 1.2mm and still got more scrub after the wheel starts to roll back( against the rockers shafts).

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I know when I went to the TD rockers they sent a gage to set my rocker stand height, they will also tell you that X amount lower or higher lift then you correct height by a determined amount, my machinist went by this system and the geometry was spot on, now this is on the paired rocker system that uses the mounting bar that is bolted to the head's