Rocker Arms 101

From simple to advanced, the rocker designs are compared from left to right. The center Pro Magnum roller features a self-aligning roller tip and roller-bearing trunnion. The Hi-Tech stainless rocker on the right features a high-strength pushrod insert to stand up to punishment at high lift and speeds.

This photo shows a comparison of a self-aligning tip (left) and a guideplate-type tip (right). The two are not interchangeable.

The self-aligning tip design on the left uses walls that extend past the roller on each side to align the rocker arm over the valve tip. In contrast, the rocker on the right has a traditional tip and must rely on a pushrod guideplate to center itself with the valve tip.

The predecessor to self-aligning rocker arms is the pushrod guideplate. These hardened plates have slots for guiding pushrods in line. Comp offers high-strength performance plates, considered a must for any performance guideplate-type head.

The four basic rocker arms for the Gen I and II SBC are shown. From left to right are the stock rocker and trunnion ball, the Comp Magnum roller and trunnion ball, the Pro Magnum roller, and finally the aluminum roller.

Shaft-mount rockers are used in some high-end builds. Their use on Gen I SBC engines is typically limited to use with an aftermarket cylinder head. However, factory Gen III and IV heads readily accept shaft assemblies. The shown shaft-mount adjustable aluminum roller kit (1.8:1 ratio) is offered for Gen III and IV engines and introduces an adjustment socket as well.

The Gen III/IV rocker arm is nothing like traditional SBC rocker arms. The stock rocker shown in the foreground is made from cast steel and features a very basic roller trunnion. The factory ratio is a whopping 1.7:1, but aftermarket ratios of 1.85:1 are common.

The traditional SBC rocker-stud size is 3/8 inch (middle). A lot of racers convert SBC studs to the stronger big-block Chevy (BBC) size of 7/16 inch (bottom). Both of these sizes dwarf the Gen III and IV M8 stud (top).

The vast majority of SBC iron heads came with press-in studs. Converting to screw-in studs is a common modification and suits performance builds. Comp Cams offers a special cutting tool for facing off the head after the factory stud has been removed. The smooth machined surface left after cutting is critical to completing the conversion properly.

Factory rockers are held in place with a special deformation locknut. Comp offers slick adjustable locknuts, which utilize a superior set-screw locking insert. These nuts are unique to the rocker type employed and should not be intermixed.