5.0 Mustang & Super FordsHow To Engine
Roller Rocker Arms
From Materials To Systems To Installation, We Show You All You Need To Know
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When most of us think about performance parts, roller rockers are usually not the first parts to come to mind. However, a good set of roller rocker arms can not only reduce friction, but also they are stronger than the stock rockers. They can even make horsepower, particularly the increased-ratio (1.7) versions.
With this in mind, we thought it was time to examine rocker arm basics. We contacted the folks at Crane Cams in Daytona Beach, Florida, and Comp Cams in Memphis, Tennessee--two of the leading aftermarket suppliers of cams and valvetrain components--to talk about rocker arm basics, from materials to the various types of rocker systems and their advantages.
We then visited Germanson Automotive and Performance in Oxnard, California, where owner John Germanson took us through some basic installations on a mocked-up 5.0.
Why Roller Rockers?
In a street/strip application, roller rocker arms are the only rockers that should be considered, because they were designed from the outset for high-performance use. Most roller rocker arms (except for some low-cost street designs) utilize a roller tip and a roller pivot point, commonly known as a fulcrum or trunion. Contrary to popular belief, the main benefit of a roller rocker is the roller fulcrum, not the tip, although both contribute to valvetrain performance and reduced friction.
Most production, stamped-steel rocker arms use a wide, flat tip that slides across the top of the valve tip as the valve opens, creating a slower, gentler valve actuation. On the other hand, a properly designed roller rocker opens the valve more quickly because the contact point is smaller and remains consistent throughout the arc of the rocker (provided geometry is correct). So all things being equal, a roller-tipped rocker doesn't significantly reduce valvetrain friction until you get into high spring pressures.
Where friction is reduced is at the fulcrum area of the rocker arm. While the rocker tip only has the valve tip to contend with, the fulcrum must bear the load of the pushrod at one end and valvespring pressure at the other. Besides the fact that reduced friction increases horsepower (Crane claims up to 25 hp can be gained), it is also believed that lower oil temperature will help the valvesprings live longer, as the oil that lubricates the rocker arms also bathes the valvesprings.
Rocker Arm Construction
Roller rockers come in various materials, including aluminum, investment-cast steel, and stainless steel.
By far the most popular material for aftermarket roller rockers is aluminum because it's easier for manufacturers to machine, it's lightweight, and it dissipates heat quickly. Though there are various alloys that aluminum rocker arms can be made from (you could write a book on metalurgy alone), suffice it to say they fall into three basic groups: cast aluminum, extruded aluminum, and billet aluminum. Cast-aluminum rockers are the least expensive because although they require expensive dies to manufacture, they become inexpensive once the dies are paid for.
Extruded aluminum rockers begin life as extruded aluminum stock, which is machined into a rocker, creating a stronger but more expensive rocker arm. Billet aluminum rockers are machined out of a solid chunk of aluminum and are regarded as the strongest aluminum rocker arms available--but they are also the most expensive by far. Cast rockers are fine for street, street/strip, and mild racing applications. For example, Crane maintains its vacuum-cast aluminum roller rockers are good for up to 500 pounds open pressure on a small-block. But beyond that, an extruded or billet aluminum rocker arm should be considered. When in doubt, contact the manufacturer for its recommendations before you purchase.
For many years, it was thought that aluminum roller rocker arms could not be used on a daily driven street car. The major reasons were that the aluminum would eventually become brittle and break and that a roller tip would not allow the valve(s) to rotate, causing excessive/premature wear of said valve. While these may have been legitimate concerns at the time, both have since been disproven.
Contemporary aluminum roller rocker arms are made from various alloys, which have dramatically improved their strength and longevity, making them more than adequate for continuous use. For example, Ford Motor Company used Crane's cast aluminum roller rockers in all '93-'95 Cobra Mustang engines, while GM used Crane's narrow-body, self-aligning aluminum roller rockers in the Corvette LT4 engine of '96. As you are probably already aware, the OEMs don't use any aftermarket products on their vehicles until they have passed rigorous, almost ridiculous, quality standards.
As far as the valve rotation issue is concerned, Comp Cams used high-speed video to see if, in fact, a roller tip did prevent a valve from rotating. Comp's findings were that it did not, and that it is the wind-up action of the valvespring that causes the valve to rotate, not the rocker-arm design.
Investment-cast steel rockers are low-cost alternatives to aluminum roller rocker arms and are typically designed for mild street/strip applications where valvespring pressures do not exceed 350 psi open. As with cast-aluminum rockers, investment-cast steel rockers are castings, making them inexpensive to manufacture. They are different, however, in they way they are cast. A cast part is one that is formed in a sand casting. Molten metal is poured into a sand mold of the part, and when the metal cools, the sand is chipped away leaving a rough mold of the part. When producing an investment casting, an exact duplicate of the part is made out of wax. The wax is then coated with a ceramic-like material and put in a furnace to fire. The wax melts out, and the cavity remaining is an exact replica of the part. This process allows the manufacturer to build an intricate design.
Comp uses the investment-casting process in both its low-cost Magnum-series steel rockers and its stainless-steel rockers, which the company regards as the strongest available. Though some may shy away from stainless-steel roller rockers because they are heavier than their aluminum counterparts, Comp maintains they are heavier only on a scale; the moment of inertia of an aluminum and a stainless steel rocker is the same. The moment of inertia is the mass that the rocker or rocker system actually sees, or how the weight rotates around the center. Whereas the stainless steel rockers are small and thin at the outer extremities, aluminum rockers are large and fat. Therefore, it is believed the actual reciprocating weight is almost identical.
Small-block Ford roller rocker systems come in two basic configurations: pedestal mount and stud mount, although shaft systems are often used in competition applications (we'll touch on those too). Which type you choose depends largely on the cylinder head you have and the intended use. All have advantages and disadvantages. However, the advantages of each system will outweigh the disadvantages if the rocker is properly suited to the application.
Pedestal-mount roller rockers are what the 5.0 engine came with from the factory, and what many cam manufac-turers offer in roller form as easy valvetrain upgrades. Pedestal-mount rockers, roller or otherwise, fasten to the cylinder head resting on aluminum pedestals that form a base for the rocker arm to rest upon. The pedestals rest in a sheetmetal channel that ties the rockers together in pairs and prevents excessive side-to-side movement of the rocker tip on valve. A long, 5/16-inch cap screw goes through the center of the rocker's fulcrum, through the pedestal, and into the boss on the cylinder head.
For most street applications, pedestal-mount rocker arms are perfectly adequate. However, when high horsepower and proportionately high valvespring pressures are used, pedestal-mount rockers have their shortcomings--the most important of which is strength (or lack of it). Though the basic rocker layout is the same used in higher-horsepower racing applications, pedestal-mount rockers employ a 5/16-inch cap screw, which has a tendency to deflect and even break in a high-horsepower application. We're reluctant to state specific numbers here because we know of many racers who have used pedestal-mount rockers well into the 500hp range with a variety of cam/valvespring combos.
The other shortcoming of the pedestal-mount rocker is its lack of adjustability. Factory rockers and some aftermarket replacement roller rockers use shims for adjustment, while other models use pushrod cup adjusters. These, however, are mainly for the purpose of obtaining correct lifter preload during installation.
Suffice it to say that if you have heads designed for pedestal-mount rockers, use them. If you get the chance to run heads that use stud-mounted rockers, do it.
Stud-Mounted Roller Rockers
Stud-mounted systems have been widely used by OEMs and are popular in street-performance applications for two basic reasons--cost and ease of adjustability. Stud-mounted systems use fewer parts and allow correct valvetrain geometry and lifter preload to be adjusted with pushrod length. The rocker is slipped over the stud, and its tip is allowed to rest on the tip of the valve stem. The pushrod side of the rocker can then be raised or lowered until correct valvetrain geometry is achieved, which is typically done through the use of an adjustable pushrod.
For the bulk of street-performance engines and many racing engines, a stud-mounted rocker system is all that will be required.
Shaft-mounted systems are typically used only in maximum-effort racing engines where budget isn't a consideration. Shaft-mounted systems are more stable than stud-mounted systems.
They also allow exact placement of the rocker tip over the valve tip, because the rocker can be moved from side to side. The same can be done in some stud-mounted applications by machining the pushrod guideplate, but this is difficult and time-consuming. Unlike a stud system, however, correct valvetrain geometry isn't always easy to obtain. Because the rockers are attached to a shaft--which, in turn, is mounted rigidly to the cylinder head--valvetrain geometry can sometimes be altered only by raising the shaft stands through the use of shims, or lowering them by machining either the stand or the cylinder head. Most stud-mounted cylinder heads can be fitted with a shaft system, but this almost always requires machine work to the cylinder head at additional cost.
To illustrate the importance of a roller fulcrum, Crane Cams conducted testing that pitted the stock, sled-type rocker arm found on a stock 5.0 Mustang engine against a Crane roller rocker arm. When the roller rockers were bolted on, temperature probes at the fulcrum area indicated the roller fulcrum reduced temperature by 200 degrees over the stock rocker.