Harney's diatribe - rocker geometry to install & beyond

[mharney]

Check me on this.. I am not a rocker geometry pro.



Dial indicator at valve fully closed : 0.8340
Dial indicator at valve full lift : 0.3055

Total lift is 0.8340-0.3055 = 0.5285

Lift of my cam is 0.575 @ 1.5 rockers (86b)
Doing the math, the lift of the lobe is 0.3833

Using 0.5285/0.3833, the lift on MY rockers gives a ratio of 1.38 using my Scat 1.25's. That works out, since that's what they really measure.

So.. half lift = 0.3055 + (0.5285/2) = 0.5698

When I rotate to that point, my adjuster is perpendicular, using no shims and a 0.080 lash cap.

Since the rocker has a radius tip, should I be using the lower adjuster cup, or do I need to go about doing it using the shaft to rocker tip angle, etc? Are these engineered so that if you don't use rocker shims, you can adjust by the angle of the adjuster? Because if I can use the adjuster, I am done and all is well with the world.

[EASY RIDER]

Mark, I don't have a clue about all that but I can say that you said a little out of context as it may be

all is well with the world.

is not a true statement.

Glad to see things moving along for you. I am stepping out the door to go and make a couple laps around Atlanta and put the other 250 miles on my engine that I need to have my first 500! I'll see what you have learned when I get back.

Bert

Do me a favor and make the DeadZone Alive and Kicking before you fire that baby up!

[A_67vdub]

When you're at half lift, look at the side view of the rockers (so the rocker shaft looks like a circle). Hold up a straight edge so you can visualize a line going throught the center of the shaft (the circle) and going to the tip of the lash cap. This line you are visualizing should be perpendicular (90 degrees) to the valve itself. If it is perpendicular, the rocker shaft is the correct distance from the head (meaning no shims required). Then look at the adjuster (we're still at half lift). It should be inline (parallel) with the pushrod. If it's not, you can adjust this by making the adjustable pushrod shorter or longer and screwing the adjuster in or out to compensate.



Steve

[ErikTheRed]

Those look like some ULTRA-beefy valve springs!

[Victor H]

It's really tough to eyeball these things. First I would install the springs you're going to run. There is minor changes in valvetrain geometry with changes in spring tension so it' best to install the regular springs.

Next take off the rockers, make sure your lash caps are fully seated, then paint the lash caps with blue dykem. Reinstall the rockers and torque the stand nuts down (make sure the rocker adjusters are where you want them). Turn the motor over for a couple of revolutions. Then take off the rockers again.

If your geometry is correct you will see the dykem rubbed off in the middle of the lash cap. Obviously, you can not use an adjustable push rod for this. Also, the geometry is determined by the height of the rocker stand, i.e. shims needed or not. Then use determine the pushrod length by where you want your adjusters to run. I borrowed an assortment from a friend and kept swithing pushrods until I got the right length. I think that is the easiest and most reliable method.

[mharney]

It seems like it is more complicated than that.

Suppose differences in setups cause a situation where the contact is at the middle of the stem (average), but the force is not parallel to the stem (average).

It seems to me that the best fit would be if the contact was at the center (average) AND the force (half lift) was parallel to the stem. I can see situations where you simply could not get there.

What part is the largest contributor? Well, hopefully, the oil is doing its job, and the POINT of contact is the most critical in that case.

It gets more interesting. If the rocker tip is not perfectly symmetric in shape, it gets a little more complicated, and that is definitely the case here.

So what to do? Go with center of stem, or figure out where the shaft must be in order for the actual force of the tip is parallel to the stem? What a mess.

[mharney]

Alrighty then..

There is no way I can get the rocker tip to hit the center of the valve stem without either:

1. having the stands machined down
2. Putting a ridiculous amount of shims in there (like 0.300")

Either one puts the geometry quite a bit out of kilter for half lift.

The Pauter rockers I had wanted you to just use the pushrods and adjuster cups, setting a specific number of turns on the adjuster cups, and just go from there.

The scat setup suggests setting the adjuster cups ALL THE WAY OUT (as in backed out as loose as they'd go if you were adjusting valves) to set the pushrod length! How the heck would you adjust your valves if they got a little tight??

[A_67vdub]

So what to do? Go with center of stem, or figure out where the shaft must be in order for the actual force of the tip is parallel to the stem? What a mess.

You want the force parallel with the stem. The reason is that proper valvetrain geometry is to minimize the side loading on the valve. When the force is parallel with the stem there is virtually zero side loading, even if a little off center, remember it needs to contact to one side or the other anyway (for valve spin), so it shouldn't be directly in the center regardless, and the side loading gets greater the farther away from parallel you get. So you want the force to be as close to parallel as possible at half lift so when you are at full lift or zero lift the force is as close to parallel as possible.

Just my thoughts, I'm no expert.


Steve

[mharney]

I'm having to have the rocker shaft blocks milled down to get there. After looking at these, figuring out where centerline was, and which way it has to go to not only get there, and also bring the rocker tip to center, the solution in my case is not to shim but to remove material and bring the shaft CLOSER to the head. I got some help from John C on what to do about it and he recommended having the rocker parts milled instead of taking material off the heads. Makes sense to me - I have a lot tied up in the heads, and modifying the rockers doesn't jeopardize the heads.

Thanks everyone for your help. Bulletins as they occur. Be a few days before I can get it done, I suppose.

[mharney]

Those look like some ULTRA-beefy valve springs!

Oh, yeah, Eric. I oughta be able to rev to the moon (at least SOME of the flying parts will make it that far, I'd bet).

I suspect you know what those are about, just a way to easily play with the valve train. The regulars are dual springs.

Had a 0.055 deck (using 0.040 copper gaskets up top) - I'd bet it will be closer to about 0.050 when full crush and break-in is over. I'll re-torque after that.

I'm gonna videotape break in, to give you all a HOOJ file to download. Not sure where I'm gonna host it yet. My webspace accounts on Cox are only 10MB each, and I'm SURE not gonna host it on my webserver here at home, it would take people forever to DL it from here.

[mharney]

Here are some pictures of my current setup. I think it's fair to say milling is the answer here.

[btljuce]

here's a little tip when checking geometry,take a black felt marker and color the tip of the valve black. install your rockers set up zero lash.then roll the motor through a couple of revolutions,remove rocker shafts and ..... voila !!! instant geometry pattern !!

[mharney]

here's a little tip when checking geometry,take a black felt marker and color the tip of the valve black. install your rockers set up zero lash.then roll the motor through a couple of revolutions,remove rocker shafts and ..... voila !!! instant geometry pattern !!

Yeah, once I get close enough to do that I will probably just use dykem.

I'm sure this is the thing to do (or try some CB's and see how they work).

[vgajames]

Here are some pictures of my current setup. I think it's fair to say milling is the answer here.

Well,try some shims under the rocker stands first before ya go cutting stuff up.See your last picture,right and visualize shims moving rocker arm assy up and the tip inward .Just try it,you'll see.Maybe a .060 and a .030 tyo start with.All motors are differant ya just have to keep trying till ya get it.

[mharney]

I've already tried. It made it worse.

Where you should be visualizing is the half lift picture (middle). The centerline from the lash tip drawn down (rough, but pretty close) is way off the centerline of the rocker shaft. Add shims, and the rocker tip gets worse.

Here is a pic at about 0.110 out. I tried about 0.050 and it was the same trend you see exaggerated here.



Now, just for fun, I did this: I stacked another lash cap, effectively changing the stem length, which is not much different from dropping the shafts. The cap total thickness was 0.182" (this is all I have that would work easy for the test, so what the hell).

NOW look. This is at half lift. Anyone convinced yet?