Rocker Arm Geometry ?

[vdcruiser]

I am having a hard time figuring out the geometry/pushrod length for the exhaust side on my BBC with Canfield heads. Some say you need to have the line through the center of the roller tip and trunnion perpendicular to the valve stem at half lift to get the narrowest contact on the valve stem and others say it is more important to get the contact patch closer to the center of the valve stem. When I get the line through the centers perpendicular to the stem the contact patch is about half way between the center and inboard side of the stem. In order to get the contact patch close to the center of the stem the pushrod has to be so long that there's not much thread left on the stud, also the contact patch gets rather wide. What should I do ?

 

[Dave Wettlaufer]

You basically want the entire scrub pattern centered on the valve, which is what you have...I think.

While I don't use their products, Comp has a simple diagram and explanation:
http://www.compcams.com/information/Products/Pushrods/

 

[Dave Wettlaufer]

While the relationship between the rocker pivot and valve tip is what determines your rocker geometry, your scrub pattern will tell you when it is right.