There is no doubt that the stud-mounted rocker systems that are commonplace on Magnum small-blocks are simpler and easier to work with. But there’s a reason why any high-end race team, whether it is NASCAR or road racing—always ditch the stud-mounted rockers for shaft-mounted systems. Shaft-mounted rocker arms are more stable, they deflect less at high rpm levels, and are generally capable of making more power.
To find out more we visited the shop of former Mopar Muscle Engine Challenge competitor Hollis Page and HP Engines in Norwood, North Carolina. Page walked us through the process on a 340 LA series small-block he’s building for one of his own hot rods.
But Mopar guys already know that. Shaft mounted rocker systems are standard equipment in all classic Mopar engines, and have all the benefits of improved valve control to go along with it. When properly set up and installed, Mopar rockers are efficient, work well even with high-lift cams, and provide trouble-free service.
But along with that improved performance also comes a few more things that need to be checked when building an engine, to make sure the valvetrain is correct. There’s a little bit more to it than simply taking the components out of their wrappers and bolting them up. Improper installation without making the proper checks, can lead to poor valvetrain geometry, or, in other words, bad angles between the components that can cause mechanical problems down the road. When everything is right, the rockers open the valves by pressing straight down on the valve stem tips. When it isn’t right, a multitude of problems can occur, including side loading of the valve stem, causing it to wear the guides, which leads to burning oil and eventually a broken valve. Bad geometry can also be the root cause of poor valve control at high rpm levels, broken retainers and even the dreaded broken rocker or valve when the rocker tip pops off the end of the valve stem.