stamped steel rocker arm delection

[Alan Roehrich]

If you can get a bigger pushrod in there, and it is legal to open up the holes in the head, you need to go with a 7/16" x 0.125" wall, at the very least you need a premium brand 3/8" x 0.125" wall 4130 heat treated pushrod. You honestly cannot get too stiff a pushrod in a race engine.

[Chris Hill]

Originally Posted by Alan Roehrich

You honestly cannot get too stiff a pushrod in a race engine.

Alan, in a stocker engine with a floppy rocker arm, is the extra stiff pushrod that important?

To quote the cliche, "You are only as strong as your weakest link." If you determine the effective stiffness of the rocker arm and then the stiffness of the pushrod, the pushrod is around 20 times more stiff (or stiffer) than the rocker arm. And since these are essentially two springs in series, the lower stiffness drives the total stiffness of the system.

[gmonde]

i did go from a 5/16 to a 3/8 chromoly push rod .080 wall,i did do some r&d on the rocker arm with several versions of welded rockers,you can get the rocker to stiffen some but you end up adding so much weight to the valve train it would be counter productive it looks like the bottom of the rocker wants to spread out ,,but if you put a rocker in small tool vise, you can see how it flexes real easy with little turning effort ,,its amazing that how much they flex but the breakage is low gmonde

[Alan Roehrich]

Pushrod stiffness prevents the pushrod from flexing, and putting its own flex and dynamics into the valvetrain. The rocker cannot even begin to do the damage the pushrod can, the pushrod becomes a spring that flexes and surges, then transfers all of that into the rest of the valvetrain.

Unless you try to make the valve end of the rocker out of lead, you're not going to make the rocker arm heavy enough to make rocker weight into a negative factor.

[Greg Hill]

One of my friends that worked at comp cams told me you can't make the pushrod side too stiff or the valve side too light.

[Wade_Owens]

Originally Posted by Greg Hill

One of my friends that worked at comp cams told me you can't make the pushrod side too stiff or the valve side too light.

Greg, I agree with this up to a point. 90% of the people we talk to are not talking about stocker level stuff. Their experience is with high lift, high spring rate stuff. Talk to Sacha at Trend. They have some cutting edge stuff right now and use a Spintron as well as some other tools for R&D. My 1.72 intake valve will take a different spring rate and pushrod diameter than a 2.02 cylinder head. It just doesnt automatically cross over....

Wade O

[Glenn Briglio]

Hey Wade have you put your stuff on a spintron? If so how about sharing some of your results.

[Chris Hill]

Originally Posted by Alan Roehrich

Pushrod stiffness prevents the pushrod from flexing, and putting its own flex and dynamics into the valvetrain. The rocker cannot even begin to do the damage the pushrod can, the pushrod becomes a spring that flexes and surges, then transfers all of that into the rest of the valvetrain.

Everything you say is correct, but why do you feel the rocker can not become a spring that flexes and surges, then transfers all of that into the rest of the valvetrain?

When I was an engineer for Eaton, the very first thing we did in analysis of a valvetrain is to determine the effective mass at the valve and the valvetrain stiffness. You then determined what the limiting factor speed wise was for the valvetrain.

Either it would be lack of valvespring force or a harmonic issue in the valve train. The harmonic issue was then divided into a mass or stiffness issue.

By far, the most effective way to increase speed is the limit mass of the valvetrain on the valve side.

On a standard pushrod valvetrain, the best place to increase stiffness is at the rockerarm. Per David Vizard's SBC valvetrain book, a SBC rocker has a stiffness of roughly 5,000 lbs/in. I've lost my previous calcs on pushrod stiffness, but I think it's roughly 50,000 lbs/in.

[Arnold Greene]

Chris, you have to find 'balance' between push rod stiffness and the valve spring controlling your valve. When you have balance, you will eliminate 99.9% of your rocker arm failures. The event that causes rocker arm destruction is the 15 to twenty thousandths valve bounce off the seat. Each valvetrain will be somewhat different due to the weight of the valve(s). BTW, the weight of a push rod has to exceed 1.25 POUNDS before it shows a negative effect on the spintron(from a great NASCAR engine builder).

Tell your folks Hi, from Lynn and I and I hope you are all well.

[Alan Roehrich]

Chris, I never said the rocker was not a problem. It is, but there's not a lot you're going to do about it. All we can do in Stock is to work on what they let us.

The calmer you make the pushrod, the less harmonics it transfers to the rest of the valvetrain, especially the rocker. The stiffer you make the pushrod, the less it acts like a spring. The less the pushrod acts like a spring, the less of a beating the rest of the valvetrain takes. If you can stop or reduce the spring effects the pushrod drives into the rocker, you can calm the rocker as well.