SB Rocker Arm Geometry

mrbill00 said
i'm thinkin' you need to raise the shaft to move the rocker tip in towards the center, your pretty close now........... or am i missing it?i
've got some shims for the old style LA head if you want to "borrow them"
....the pattern in the center is a good thing..and we're assuming the correct length pushrods
DvorakMachine has an tech article about this
let me know

Raising the shaft will only make it worse. I had the exact same problem he has and tried installing shims and it moved the roller closer to the end of the tip and nearly rolled off at full lift. You really have to study it good to see what's happening. It's because the angle of the rocker shaft stands aren't perpendicular to the valves that throws a person off in thinking it needs to go up to move the tip closer to the shaft when in reality it's just the opposite. Only lowering the shaft (by cutting down the stands) or raising the valve tip height will move the roller closer to center. I've been through it just last year.

mrbill00 said
from "Dvorak's papers"..
improper geometry will look like the rocker tip is scrubbing toward the exhaust manifold side of the valve tip for the entire lift cycle OR PULLING back on the tip of the valve toward the shaft side during the entire cycle.

IT IS IMPERATIVE THAT THE TIP OF THE ROCKER CHANGES DIRECTIONS AS IT "SCRUBS" ACROSS THE VALVE TIP.

A roller tip rocker is okay if the roller center is on the center of the valve tip at half lift in most cases. Raise (with shims) or lower (by machining the pedestals or the shaft stands until you can accomplish that position. But if you observe the movement across the valve tip it should do the same as described for the stationary tip rocker. And that is start contact to the shaft side of the valve while the valve is closed, move across the tip just to center or slightly past, and then return to the original position during full lift. Then back to center at one half closed and back again to the original position when the valve is closed.
,,,see his website for more indepth stuff..

Dvorak machine does have some good info about valve train geometry but I think when they say "IT IS IMPERATIVE THAT THE TIP OF THE ROCKER CHANGES DIRECTIONS AS IT "SCRUBS" ACCROSS THE VALVE TIP their referring mainly to non roller tip rockers. Standard non roller tip rockers would create alot of side loading when the geometry isn't right. With roller tips almost no side loading is present. Also on a Mopar pushrod length has absolutely nothing to do with rocker arm geometry because the rockers are mounted on a shaft that doesn't change height. Unlike a Chevy whereby the rocker changes height with just adjusting the valves the pushrod is the main factor in correct geometry.