As complicated as engines can be, they are remarkably resilient. When it comes to valvetrain stability, it's critical to get the tolerances correct for the utmost power and longevity. This means having the proper pushrod length and making sure the rocker arm is centered on the valve tip itself.
Simply put, rocker arms are designed to make contact at the top of the valve tip, with minimal movement. Think of the valve tip in three stages: top, middle, and bottom. The top, facing the intake side of the center, is where it starts from the base circle of the cam. From there, the rocker will move to the center, where the cam is at midlift. The final sweep is at the bottom, where the rocker is seeing maximum lift. This is the ideal geometry for a rocker arm.
If the rocker is not centered, however, you're opening up the door for a host of problems. Simply using the wrong pushrod length will cause the rocker arm to touch the valve tip either too far behind or forward, and that can cause the rocker to run across the entire valve tip and possibly bend the valve stem. This, in turn, can start a volatile chain reaction resulting in unnecessary engine friction to worn-out valveguides and possibly breaking the valves from side load stress. And if you didn't already realize it, more aggressive camshafts will only aggravate the problems.
The fact is, rocker arm geometry shouldn't be taken lightly. You need to realize that every engine build varies. Even off-the-shelf combinations can differ based on the block deck height, head stud boss height, varying brands of lifters, and cam base circle size. If there's a problem from the beginning, be sure to address it. Every once in a while we still hear of people clearancing rocker arms because it's hitting the retainer. If it's hitting the retainer, you're having other issues and should size up the pushrod appropriately. All said and done, it doesn't cost much to do and it's easy enough to check.
Quick Notes
What We Did
Checked for proper pushrod length
Bottom Line
Accuracy is key
Cost (APPROX)
$17 for a Comp Cams adjustable pushrod