Volume III, Issue 7, Page 23

Turn the channel back a couple dozen years. If someone popped the hood on a Chevy and spied aluminum valve cover spacers, chances were the car was a serious effort. The spacers insinuated that the engine was wearing an exotic stud girdle and was fitted with equally alluring roller rocker arms. The probability was also good that that particular machine was a rocket ship.

Fast forward to now: Rocker cover spacers have all but disappeared and stud girdles aren’t even as common as they once were. Instead, the valve train has progressed to the point where sophisticated rocker arm systems are the norm rather than the exception.  

Most rockers are made of aluminum, but a few are steel, and they all work off a rollerized bearing. What’s the big difference?  Aside from the fact that the rockers on the left are stud mount and the rocker on the right is a shaft mount, there’s a bunch of difference between the two. The images following give more insight.

At one time it was sufficient to replace a stamped rocker with a rollerized one. Now we’re dealing with shaft rocker setups privy to countless upgrades and options.  To see a car with valve cover spacers simply proved it was a bad-to-the-bone piece and that it was a force to be reckoned with, but it also meant you were at war with the entire assembly when it came time to set the valves. Typically, you loosen the stud girdle and then you lash the valves. You re-tightened the girdle and check the valve lash once more.  If the studs are the least bit out of alignment, tightening the stud girdle changes the valve lash. But you also have to be extremely careful with clearances on some combinations-–the rockers and girdle can contact one another, spelling instant trouble. 

This Jesel rocker (for a big-block) might not look as fancy as a more common polished or anodized stud roller rocker, but don’t let appearances fool you. This Competition Series item is machined from 7000-series aluminum alloy, and the surface has been shotpeened. Jesel points out that “shotpeening induces an even, compressive stress layer in the surface of the rocker body” thus increasing the rocker’s resistance to failure due to fatigue, which in turn, increases the cycle life of the rocker arm. (FYI, you can also purchase shaft rockers manufactured from 2024 alloy.)

That should be enough for most people to re-think the valve train arrangement, but there’s a wee bit more:  In a small-block, the stock rocker has a relatively short pivot length, implying that the arc it travels in is small, particularly in comparison to other engines (Jesel points out the stock small-block has a rocker pivot length of 1.40-inches.  In contrast, a big-block has a pivot length of 1.65-inches).  This means that the stock small-block rocker arm tip more or less scrubs across the tip of the valve as it opens.  This isn’t much of an issue at lower gross valve lifts such as those experienced with stock or mild camshafts, but if you increase the lift dramatically and increase the spring pressure, you’re soon faced with another dilemma:  Increased friction.  How much friction?  Long ago, Danny Jesel relocated the rocker studs away from the valves on a small-block Chevy, so he could incorporate big-block rocker arms. In a rotating torque test, it took 80ft-lb less torque to rotate the small-block with big-block rockers in comparison to a stock rocker small-block.  That’s a bunch.

To gain pivot length on a rocker arm, it’s not that easy to relocate rocker studs on any engine.  However, you can’t change the rocker pivot length and correct the rocker geometry unless you move the pivot point.  It is far simpler thing to build an entirely new rocker arm arrangement such as today’s shaft rocker.