I just installed new heads. I have an adjustable pushrod but I need to get a set of calipers long enough for it.

I tried the stock 7.8 inch push rod with my roller rocker and got this. What do you think shorter longer ok? Patriot says a 7.8 usually works well.

 

Contact should be in the middle, I say shorter

 

What does the sweep look like?

 

Doesn't matter where on the tip the contact is (within reason). Specifically, there is NO REQUIREMENT that it be centered. Not sure how that myth got started but it sure would be nice if it would die. Where yours is, is fine.

Look for the narrowest possible "sweep". That's the TRUE indicator.

What you have doesn't look too bad. Only way to know if it's "best" is to change the PR length and try again.

 

I will get a picture of the sweep. In reality it is about the same place the stock heads with the stock pushrods were with these rockers. I will crank ir over and check the sweep.

 

Here is the sweep I did it twice and cranked over the engine twice looks really similar to the stock heads.

 

So, when you put your adjustable push rod in there and set it .050" shorter and .050" longer, how much did it improve? Show us those pics and we'll be able to tell you if you're optimized or not.

 

Too far out on the valve stem. You need shorter pushrods, thinner head gasket or longer valves. Although it doesn't need to be exactly centered, the closer you can get it to the center, the better.

 

May I repeat:

It DOES NOT MATTER where on the stem the pattern falls, within reason. What matters is getting the NARROWEST POSSIBLE sweep, which indicates proper geometry, since that corresponds to the rocker's arc being centered around mid-lift, resulting in the greates possible lift and least possible side load.

DO NOT WORRY about where on the stem it falls. DO NOT choose push rod length by where it falls. Choose push rod length to get the NARROWEST POSSIBLE SWEEP. Which you cannot know what that is, until you try different lengths.

 

ill just start off by posting.

if it's a stocker that not seeing over 4000 rpm.and all the parts are factry.
it would be more centered then that. in your pics.
parts are made to size for a proper fit..(Myth)?

for a long and helthy life you want it more centered on the valve tip.

by doing so it cuts down on the side loading of the valve.
and puts less stress on the Guids (spelling).

this is a simple Fact! and Not a MYTH...lol

IF IT WAS a myth then every body and there Dog would be just slapping parts together and never dropping a valve. from rocker roll off
or valve tipes getting chewed up from the same..

whats nexed ya only need 4 lugnuts..cuzz all dem imports only use 4

take it from Guys who run this stuff all the time in the uper RPM.
and from anybody who makes the parts. and uses them.

you will sleep better at night

and a side note with the rocker running in the midle of the valve.
the sweep will be the same has it is all the way out on the side

now go get some shorter push rods

 

If you have a 1/2 hour to spend read this thread about mid-lift theory. Myself I use the least amount of sweep theory as long as the rocker sweep center is in the middle 1/2 of the valve stem.

http://www.speedtalk.com/forum/viewt...iller+mid+lift

 

went and took a read..

them boys sure can make a sling shot into a Moon Shot. WoW!

Like i posted.. move it more to the center of the valve.

it will live longer and all will be right in the world!

 

Where the rocker arm contacts the valvestem face does matter if its way off to the side. Ideally you want it near center. If its way off to the side, it puts a lot of load on the face, and can cause mushrooming and pitting because of the excessive loads.

I attached a pic. Its kinda crappy, but hopefully it helps illustrate what Im saying.

One thing Ive found with the "least area method" is that it tends to move the rocker tip out to the edge of the valve. In my case, the rocker tip was nearly off the edge at mid lift. The reason for this is that the rocker fulcrum needs to be up higher to have the smallest contact pattern. Since the stud and valve-stem are not parallel with eachother, the rocker fulcrum moves out towards the valve stem centerline. What the smallest pattern is actually is the rocker arm tip traversing a symetrical circular arc. Supposedly this is best because it has the tip traveling the least. But if you think about it, it has the rocker tip actually moving backwards past mid lift at peak spring pressure. This can be worse in some cases since it forces the tip to move under max load, and can side-load the valve stem.

The factory method is such that the rocker tip is near the tangent of the circle that it traverses near peak lift. By tangent, I mean the tangent that would be formed by the circle the rocker traverses, and the centerline of the valvestem. This results in more motion of the tip initially, but the tip is almost stationary at max lift and spring pressure. This is shown in the inset called "Path of rocker tip." The obvious advantage is that the tip doesnt move much when its loaded the most heavily, which is a real plus with standard stamped rockers with sliding tips.

With roller rockers, its more of a wash since they roll. But, when it comes to location, it does matter. There are very high contact stresses on the valve stem face in excess of 100,000 PSI for performance springs. Having the contact out towards the edge increases this pressure. This is especially an issue with full stainless steel valves that arent as hard as steel ones, or ones with special spun-welded faces.

I prefer the factory method as it keeps the rocker lower, and keeps the rocker tip more near the center of the valve, and almost invariably uses the stock length pushrod. The only drawback is that its harder to set up as you cant just use the contact pattern to determine the correct pushrod length.

 

IT DOESN'T MATTER WHERE ON THE STEM THE ROCKER LANDS, within reason. As long as it's not falling off, it's FINE.

To illustrate why, perform the following experiment:

Lay a bencil on your desk. With the tip of another pencil, push it straight in line with its length, right in the center of the eraser. Which way does the pencil move?

Now push it straight again, except out toward the edge of the eraser. Which way did it move?

Now push it at a slight angle, right in the center of the eraser. Which way did it move?

Conclusion: which feature of how you pushed the pencil made more difference in how straight it moved: the place, or the direction, that you pushed it?

Not too hard to see what matters, eh?

The narrowest sweep corresponds to the straightest push. Pushing at the center but in an off-axis direction corresponds to jacking the push rod length so that its arc of movement is no longer centered, causing it to slide across the rocker tip more instead of just pushing it, which is where guide wear comes from; and costs lift as well, because more of the motion of the cam lobe, lifter, and push rod, is consumed in moving the rocker tip SIDEWAYS instead of UP AND DOWN.

Don't worry about where the pattern lands on the valve stem tip, WITHIN REASON. THe correct geometry occurs with the NARROWEST POSSIBLE SWEEP, regardless of where it occurs on the stem (within reason).

Google "mid lift rocker geometry" for some instructive reading. Try to ignore Mr Miller's somewhat egotistical writings on the subject and concentrate on the diagrams.

 

This is sort of like butter side up toast, or butter side down toast. Especially with roller rockers, it doesn't matter much provided its within the center 1/3 of the valve stem face. Anything outside of that will cause issues in my opinion.

Now, whether one method costs lift is something that's not so easily determined. The rocker tip moves in a circular arc, so its not just sliding, but translating in two directions with respect to the valve stem face. Even in the narrowest sweep method, it still translates back and fourth across the face of the valve stem.

 

Thanks for the info guys. I have a plan now. I am going to finish reassembling with the 7.794 inch pushrods and drive it the 2 miles to its storage place. From there I will play with the geometry more. I don't want to rush it but I also don't want to get caught in the snow trying to get it stored for the winter.

 

I wouldnt loose any sleep over it for just a short drive to storage. Its not that big of an issue so long as nothing is binding.