Off Your Rocker: 4 Reasons It Might be Time to Step up to Shaft-Mount Rockers

At first glance, most roller rockers look the same. 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. And yes, Summit Racing has all of the rockers shown available to you. More in the next photo…

This BBC Jesel shaft rocker might not look as fancy as a more common polished, anodized stud roller rocker, but looks can be deceiving. This rocker is machined from 7000-series aluminum alloy, and the surface has been shotpeened. Jesel notes “shotpeening induces an even, compressive stress layer in the surface of the rocker body.” What does that mean? Simple. It increases 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 or from steel.

Viewed from the bottom side, this rocker is “centered”. That means no offset has been built in. Typically, you can order rockers for just about any cylinder head combination out there. If the head is designed with a pushrod offset, then the rocker can be specified with a matching offset.

This Jesel big block rocker has a pivot length of 1.650 inches. It is a standard model with a lightening slot in the center. The weight is 202 grams. A solid body model tips the scale at 210 grams while a highly profiled rocker (Jesel calls those model series “Mohawk”) weighs 195 grams. In comparison, we weighed a common stud mount standard roller rocker, and complete, it weighs approximately 194 grams. There goes the theory that shaft rockers are way heavier than stud mount jobs.

Examine the backside of this rocker. It has been profile machined. It provides more valve cover clearance and it also peels some weight out of the rocker. Simultaneously it improves the moment of inertia. What’s “moment of inertia”? Think of a spinning figure skater. At the beginning of the spin, the skater’s arms are extended. The rotation of the spin is relatively slow. As the skater’s arms are pulled closer to the body, the speed of the spin increases rather quickly. With arms extended, the skater’s moment of inertia is high (the spin is slower), resisting the speed of rotation. Moving the arms inward lowers the moment of inertia, which in turn creates far less resistance to the rotation (the spin is faster). The same applies to a rocker arm--less body at the back of the rocker makes it easier for the rocker to change direction.

The bearings for the shaft are most often of the needle variety (typical of most roller rockers, shaft or otherwise). This particular Jesel shaft rocker incorporates Timken bearings. There are also shaft rockers available today that operate without bearings. Instead, a special bushing is used.

There are several different tip roller setups used on shaft rockers. This is a standard roller but you can also specify needle-bearing roller tips in varying sizes (Jesel offers options of 0.250-inch diameter or 0.360-inch diameter). Needle bearing tips are designed for use in high lift, high spring pressure applications where in certain cases, the roller can “stall” (stop rolling) and consequently skid across the valve tip. Tips can be locked in place with a heavy c-clip device or they can simply be pressed into place, depending upon the rocker.

The adjuster system used on a shaft rocker is considerably different than that found on a stud mount rocker. In a stud mount rocker adjustment is accomplished right on the stud (which basically determines how much the rocker can move up and down on the stud). On a shaft setup, adjustment is set on the pushrod. Once you set the lash, the rocker simply rotates to take up the lash. There’s no real trick to setting lash on a shaft setup either--just like a conventional rocker, the feeler gauge goes between the valve tip and the rocker tip. Only the adjustment location differs.

Here’s an up close look at the jam nut and adjuster screw used on the standard Jesel rocker. The jam nut is a 12-point model (7/16-inch box end wrench) while the actual adjuster uses a 1/8-inch Allen key. Jam nuts are typically heat-treated alloy steel on standard and lightweight rockers. Several different types of adjusters are available, including tool steel ball lash adjusters, however most of those are used in NASCAR applications. Ball lash adjusters offer less friction than cup format adjusters, and they’re a bit stronger because they increase the adjuster area by eliminating the counter-bore for the standard cup. Keep in mind a ball lash adjuster mandates unique pushrods.

Jesel notes that the operating range for the lash adjuster is ¼ to 2 full turns out from the seated position. If the adjuster needs to be set more than two turns out, this means the pushrod must be 0.050-inch longer. If the adjuster is set less than ¼-turn turn from the seated position, that means the pushrod must be 0.050-inch shorter...

...That’s why a pushrod length-checking tool set (second photo) is included with many shaft rocker setups.

Stands for shaft rockers are configured for each type of cylinder head (and as you can imagine, the combinations are staggering).

This particular stand combination is for a 24-degree Brodix -2 style head. Fasteners are special large diameter, shallow head ¼-inch Torx models.

Jesel includes a 3/8-inch drive Torx socket with each rocker shaft kit. In this application, there are several ports where the hardware protrudes into the port. Obviously, in each of these ports, sealant has to be used on the fastener to eliminate vacuum leaks. Additionally, if longer than stock valves are used, you’ll have to shim the rocker stands to maintain valve train geometry.