Flexing Rocker Arm Muscle

Back in 1955, the Chevy smallblock was one of the hottest V8 engines you could get. Its ball and stud stamped steel rocker arms were a revolutionary departure from the shaft-mounted rocker arm systems of that era because they allowed the SB Chevy to outrev its competitors. More revs means more airflow and more power.

It wasn’t until 1962 that Ford finally dumped its old Y-block 312 rocker shaft engine and replaced it with the 260-289 series of engines with ball and stud rocker arms.

For the next decade, Ford and Chevy competed for predominance on drag strips, road courses, circle tracks and on the street. As engines struggled to achieve higher and higher rpms, the limits of the stud and rocker system soon became apparent.

Though free-floating rockers were capable of high rpms and loads, the studs that support and position the rockers were not.

Stiffer springs are obviously needed to prevent valve float at higher engine speeds. But double springs and triple spring with high seat pressures also put more load on the rocker arms and studs.

Replacing the stock stamped steel rockers with stronger and lighter forged aluminum needle bearing rockers improved strength, and replacing the stock push rods with thicker and stiffer push rods improved reliability of the valve train, too.

But the limiting ­factor was often the studs that supported the rocker arms. Pressed-in studs could only handle so much force before they started to pull out of the boss in the cylinder head. So one modification that racers had to make was to drill and pin the studs so they wouldn’t pull out.

The introduction of screw-in rocker arm studs solved the pulling problem, but did nothing to improve stiffness. A stud is only supported at one end, so when the rockers are under high load at high rpm, the studs can flex quite a bit. The motion in the stud upsets valve lash, valve lift and overall valve train control.

The fix for stud flex was the introduction of the stud girdle. Clamping a rigid bar to the tops of the studs provided the extra support needed to minimize stud flex.

But the girdle also created a barrier that made adjusting stud-mounted rockers a chore. Even so, the stud girdle seemed to provide the answer everyone was looking for — that is, until the reintroduction of shaft-mounted rocker arm systems for high performance engines.

Back to Rocker Shafts
The move back to rocker shafts actually came about by accident, according to one story. A performance engine builder named Dan Jesel had just assembled two engines for a customer. One was a small block 302 Chevy and the other was a big block 427 Chevy.

As a final check, Jesel would rotate the engines with a torque wrench to make sure nothing was binding. Both engines checked out fine, but the Chevy small block required approximately 80 ft.-lbs. more torque to turn over than the big block.

That didn’t make sense to Jesel. If anything, the big block should have required more torque because of its larger cylinders.

Worried that something was amiss, Jesel tore down the small block and inspected everything. No problems were found. Yet the engine still required considerably more torque to turn over than the big block.

His “Eureka” moment came when he realized the stud-mounted rockers on both engines had different lift ratios. The small block had a rocker pivot length of 1.4” versus 1.65” for the rockers on the big block motor. The big block rockers had a larger arc, which produced less scrubbing on the valve tips as they opened and closed the valves.

To test his theory, Jesel relocated the rocker studs on a set of small block Chevy heads to see how changing the pivot point affected friction in the valve train. When he rotated the engine with his torque wrench, he found the new location reduced torque 80 ft.-lbs. The small block now turned as easily as the big block motor. Less drag meant the engine could make more usable horsepower.

So Jesel began relocating the rocker arm studs on all of his customers’ small block Chevy engines to take advantage of his discovery.

Relocating studs required a fair amount of work, so Jesel designed what became the first aftermarket shaft-mounted rocker system. The shaft stands bolted to the standard stud bosses on the head, making installation easy. The offset location of the shaft also relocated the rocker pivot point to provide the reduction in friction Jesel wanted. He could also design the shaft system to offer any lift ratio a customer desired.

Benefits of Shaft-Mounted Rockers
A number of aftermarket companies now offer shaft-mounted rocker systems for a wide variety of engine applications and aftermarket cylinder heads, everything from the common small block and big block Chevy and Ford engines to the latest LS1 family of engines.

Regardless of who makes them, shaft-mounted rockers have become the hot setup for most forms of professional racing. Shaft-mounted rockers typically cost $600 to $1,400 for a set, depending on the engine application and the supplier. But, they have a number of important advantages over their stud-mounted counterparts:

• Increased rigidity and reliability. Supporting the rockers on a rigid steel shaft means the rockers can’t deviate from their fixed location due to stud flex or vertical motion on the rocker stud. The stiffness provided by the shaft holds all the rockers in perfect alignment and allows them to safely handle higher loads and rpms — which is a must for professional-level racing. For extra durability, some suppliers offer steel rocker arms with their shaft-mounted systems.

Shaft-mounted rockers also don’t require a slot in the underside of the rocker to accommodate a stud, so the rocker arms are inherently stronger.

• More horsepower. Reduced valve train friction combined with improved valve train rigidity means the engine can handle higher lift ratios and seat pressures while still maintaining accurate valve timing and control. If you’re building a high-revving engine with valve spring pressures of 1,000 lbs. or higher, a shaft-mounted rocker system can provide the strength and control that’s needed.

• Easier installation. Most suppliers of shaft-mounted rockers work closely with aftermarket cylinder head companies to create bolt-on systems that are designed for specific cylinder heads. This eliminates or minimizes the amount of machine work that’s required to adapt a shaft-mounted rocker arm system to a particular head. Most suppliers can custom make a shaft-mounted rocker system for almost any motor with any offset or lift ratio you require.

• Easier valve lash adjustments. Shaft-mounted rockers typically hold valve lash adjustments longer, and are easier to adjust than stud-mounted rockers with a girdle overhead. The adjusters on the rockers or the shaft are easy to get at and adjust. For a weekend racer, this can be a real time-saver between rounds. If the rockers don’t have to be adjusted, there’s no need to pull the valve covers.

To find out more about what’s available to engine specialists, we contacted the following companies for more information about their shaft-mounted rocker systems. Note: This list is extensive, but it’s not exhaustive because other companies told us that they don’t supply shaft-mounted rocker arms or only supply those made by other manufacturers.

Comp Cams
Competition Cams has shaft-mounted rockers for small block and big block Chevy and Ford engines, also Edelbrock’s P8 Pontiac head, Chevy Brodix and Dart heads, and RHS big block Chevy heads.
Most of their focus has been on developing new shaft-mounted rockers for the Chevy LS market, while systems are available for the LS3 and LS7 applications, and many others will be coming soon.

The company said engine specialists should look for three attributes in any rocker system; the preeminent feature you want is stiffness and they said their shaft rocker systems feature an extremely rigid mounting system. This keeps the trunion and bearings in place as the rocker is loaded and rotates about its axis. With any stud system, the studs flex considerably. Going from 3/8” to 7/16” certainly helps, and stud girdles are a further improvement over the stock system. However, no stud system can match the stiffness of a well-designed shaft rocker system.

The second attribute you want is low rotational mass in a rocker system.

The third and final attribute to look for is true and consistent ratios. Because it is difficult to consistently set up stud-mounted rockers at the same height, there is also much more variation in ratio from cylinder to cylinder and engine to engine when dealing with a stud-mounted rocker setup. With a shaft-mounted rocker system, one can improve on each of these critical areas.

Although Com Cams’ shaft systems are designed for easy installation, they are intended for race applications. Consequently, some machine work may be required to properly install a shaft rocker system.

One installation tip is to carefully check the sweep of the roller tip across the valve when setting the stand height. The initial motion of the tip should be outward, with the tip changing direction between 1/4 and 1/2 of maximum lift. This results in the truest ratios and maximum stiffness.

Also, make sure to select the proper length pushrods. Although the adjusters will allow a shorter than optimum pushrod length, Comp Cams recommends that the pushrods are the last component selected. Use an adjustable “checking” pushrod to determine the proper length. Start with the seat all the way in the body. Then turn the pushrod adjuster out one half to one full turn from bottom for maximum strength.

The manufacturer  also cautioned engine builders to not be fooled by exceptionally low-priced valve train components just to save some money. While knock-off parts are clearly flooding into other valve train markets, the shaft rocker segment has not been a major focus. However, no segment is safe. On any engine build, you must have 100% confidence in the company you are buying from. The absolute last place you ever want to skimp is on the valve train because there’s no such thing as a minor valve train failure.

Crower Cams
Crower Cams has been making shaft-mounted rocker systems for about eight years, and makes systems for most of the aftermarket cylinder heads made by AFR, Brodix, Dart, Edelbrock and World, as well as OEM heads for small block Chevy and Ford, big block Chevy and LS1 Chevys. As they move forward, Crower Cams plans to introduce more variety and expand its shaft-mounted rocker product line.

Crower offers systems with either aluminum or steel rockers. Most of the systems they build are custom pieces for professional racers, however, they can give them any lift ratio they want and design the stands for their valve lengths. A typical custom setup costs about $1,350, and everything is made in the USA.

The company said that lately there has been more interest in shaft-mounted rocker systems among oval track racers. Drag racers have been using shaft-mounted rockers for years, but the oval track guys are now starting to run higher rpms with lots of spring pressure and radical cams. For that, they need a shaft-mounted rocker system, a Crower representative said.

Harland Sharp
Harland Sharp has had a full line or shaft-mounted rockers for small block Fords for a number of years, as well as shaft rocker systems for all the popular aftermarket heads (AFR, TrickFlow, Brodix, Dart, etc.).

Its small block Chevy system is different from many of the other rocker systems that are out there in that it uses a new mounting system with machined aluminum base plates. The shaft has no bolt holes passing through it, and is supported by the stand uprights. The shaft is 11/16” diameter 52100 tool steel, with two rockers on each shaft. Available rocker ratios range from 1.5:1 to 1.75:1.

These units were introduced at the Performance Racing Industry show a few years back.

The company has also developed a similar setup for big block Chevy applications. The only difference is that each big block rocker is mounted on its own shaft.

Harland Sharp says most of the shaft-mounted rocker systems they make are custom built for specific engine applications. And that they design each system according to valve lift, spring pressure and the amount of offset a customer wants. A typical selling price is $1,000 to $1,300.

Jesel
Jesel, which has been making shaft-mounted rockers for more than 30 years, has worked with Edelbrock to ­develop shaft-mounted rocker systems for some of their new cylinder heads, such as the 18° Big Vic head.

A Jesel speokesperson said the company has products for almost every application.

“The Chevy LS market is really growing, and there are a number of new heads for those engines. We are working with the cylinder head manufacturers to develop shaft systems for their heads. These will be bolt-on installations designed to handle higher spring pressures and lift ratios,” he said.

Jesel uses aluminum rockers primarily, but are also making some steel rocker shaft systems for NHRA Pro Stock racers and endurance road racers. The company also makes a new shaft system for the 6.1L Hemi for drag racing.
Jesel said many Pro Stock drag racers buy raw head castings and do all of their own machine work, so the company does a lot of custom shaft-mounted rockers for those racers. The company also does a lot of repair work and rocker rebuilds for other drag race classes, too.

According to Jesel, a Sportsman rocker shaft system for a small block Chevy sells for around $1,000, compared to around $1,400 for a custom Pro Series system for the same engine.

Probe Industries
Probe has shaft-mounted rocker systems for small block Chevy and Ford, big block Chevy and many popular ­aftermarket performance cylinder heads.

Its rocker systems sell for $663 to $1,000, and most are bolt-on installations, except on the big block Chevy which requires some machine work.

The big block kit includes a jig for locating and drilling the holes to mount each rocker support stand.

A Probe spokesperson said shaft-mounted rockers can handle spring pressures up to 1,200 lbs., and improve valve train stability at all engine speeds. They also said because one can get a true lift with a shaft-mounted rocker system, you don’t need a bulky stud girdle.

Probe’s shaft-mounted rockers come with CNC-machined aluminum rocker arms that have dual needle roller bearings, and steel support stands. Available rocker ratios are 1.5:1 and 1.6:1.

T&D Machine
T&D Machine said it provides a lot of secret stuff for NASCAR Cup racers and they can’t comment much about it, except that its shaft-mounted rockers are providing those racing teams with the performance they request.

The company said Nationwide series cars have an eccentric system that doesn’t have a traditional adjuster on the rocker arm. You rotate the rocker shaft to change valve lash with this system.

While some Sprint car racers have tried it, most want a lighter rocker arm. The eccentric system comes with steel rocker arms, which provides a lot of strength and durability. For the Sprint car racers, T&D said its shaft system with aluminum rockers is better.

T&D Machine makes more than 400 shaft-mounted rocker systems for a wide variety of engines and aftermarket cylinder heads. Applications include small block Chevy and Ford, Buick V8 and V6 engines, and Chrysler small block and Hemi. Latest applications include shaft systems for Edelbrock’s 409 Chevy head, and their Pontiac and Oldsmobile heads.
While they do a lot of custom one-of-a-kind shaft rocker systems, too, the company said turnaround time takes about a week on average.

T&D Machine’s off-the-shelf basic rocker arm sets start at around $700 for a small block Chevy, and go up to $1,000 or more for a custom set. All systems are made in the USA.

The company offers both aluminum and steel rockers. The steel rockers cost about 25% more, but they are almost as light as the aluminum rockers and much more durable. A spokesperson said the blown alcohol and nitrous oxide drag racers love the steel rockers because they hold up so well.

Though the shaft-mounted rocker systems are primarily for racing, some people do use them on the street. A spokesperson said that they do not recommend running aluminum rockers on the street if a customer expects to get a lot of miles out of an engine. Steel rockers would be the better choice.