By Mike Mavrigian
ROLLER ROCKERS
This refers to rockers that feature both a needle bearing trunnion pivot and a roller wheel for valve tip contact. Full-roller rocker arms reduce friction and provide a more accurate means of valve control and stability as opposed to factory rockers that feature a friction-laden pivot and rubbing friction between the rocker and the valve. A full roller rocker may be stud mounted to the head or pivots on a rocker arm shaft, wherein the shaft is bolted to the cylinder head, with the rocker bearing pivoting on the secured shaft. The reduction of friction should be obvious. Full-roller rockers available for small block Chevy applications include forged or billet aluminum or tempered steel, in a variety of shapes, weights and arm ratios.
When 18-degree or shallower valve angles and the use of larger diameter valves, it’s common to require the use of offset rocker arms in order to maintain rocker arm alignment to both valves and pushrods. The rocker arm offsets will be determined by the specific cylinder head manufacturer. As but one example, a set of Trick Flow 18-degree heads will require exhaust rocker arm offset of .220-inch and intake rocker arm offset of .550-inch when using Jesel rocker arms. The cylinder head manufacturer will usually recommend one or more specific rocker arm brands as well as offsets to properly accommodate their heads.
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Valve cover height/width dimensions are a clearance consideration, since beefier aluminum rockers may not accommodate “standard” OE-style valve covers. Taller aftermarket valve covers are readily available, so this isn’t an issue of great concern. Just make sure you check for clearance. When you’re dealing with heads that feature shallower valve angles than the traditional 23-degree valve angle, offset rockers are required, which places further clearance restrictions relative to the valve covers at the inboard/intake sides of the covers. In this case, wider valve covers, often involving “sheet metal” or “welded” covers, are needed. These covers feature wider-spaced walls, which places the walls beyond the bolt hole flange lips of the head. As a result, the covers feature recessed/pocketed bolt hole locations that accommodate the wider walls while still bolting directly into the cylinder head holes.
SHAFT MOUNTED ROCKERS
High performance roller rocker arms are available as stud mount or shaft mount. In the early days, stud mount rockers pivoted via a ball and socket design. As higher performance requirements were needed, aluminum and steel rocker that pivot on a roller bearing were employed. As development progressed, a roller bearing was added to the rocker’s valve tip. With more aggressive cams and higher engine speeds and loads increased, stiffer materials were employed and various geometric rocker arm shapes were developed. The next step in the evolution was to offer shaft mounted rockers. Instead of each rocker pivoting at a single stud, a horizontal shaft serves as the fulcrum point, which greatly increases both mounting stiffness and valvetrain stability. Since the rockers pivot on a common shaft, this prevents the rockers from individually deviating from the axis of the valve, which results in superior rocker-to-valve and rocker-to-pushrod stability. Stability is optimized since the rockers can only pivot on their shafts and can’t move laterally across the valve tips. Also, since each shaft secures to the head with multiple bolts, this provides a more stable and strong mounting platform ideal for high engine speeds and loads.
ROCKER ARM MATERIALS
Performance roller rocker arms, depending on the manufacturer and what series, or types offered, may consist of precision-cast stainless steel, forged or high-temper aluminum, chrome-moly steel or other steel alloy materials. Aluminum requires a thicker design as compared to steel. Although they are lighter, they tend to be bulkier, which in some cases can cause interference issues with valve covers and some heads. “Lightened” steel rockers can be made using reduced dimensional mass to approach the lighter weight of aluminum. Although generally heavier, they can be designed to achieve the same moment of inertia as aluminum. The bottom line is that these are generalities that really don’t amount to much of a concern. The goal is to use rockers that suit the specific application. The higher the spring pressures, the stronger the rocker and its mounting platform needs to be. For all-around performance and racing use, aluminum rockers are available for just about anything you plan to build. If you plan to run endurance races where high 8000 – 9000 RPM use will be constant, high strength steel may be the better choice. A variable is the manufacturer and series of rockers each maker offers, since some are stout and full-bodied and some are lightened and feature strengthening ribs, and the quality and design of bearings and trunions can differ. All aluminum rockers are not equal, nor are all steel rockers equal. The bottom line is that if you choose rockers made by a seasoned and reputable maker, chances are they’ll have what you need. Just stay away from low-priced offshore rockers. Avoiding potential failure during extended high-RPM runs is worth the extra cost.
ROCKER ARM RATIO
Rocker arm ratio represents the comparison of two pivot point distances…the distance between the centerline of the rocker arm pivot (the trunnion bearing, where the rocker rides on its shaft or stud pivot) and the centerline of the rocker arm’s roller tip, where it meets the valve stem tip; compared to the distance from the pivot centerline to the pushrod cup. The distance between the pivot centerline and the pushrod cup centerline is referred to as distance X. The distance from the pivot centerline and the roller tip is distance Y. Distance Y is also referred to as the rocker arm’s pivot length (more on that later). Ratio is determined by dividing distance Y by distance X.
For example, if distance X (pivot center to pushrod cup center) is 1.000-inch, and distance Y (pivot center to roller tip center) is 1.500-inch, Y divided by X is 1.500-inch, in which case this rocker arm has a ratio of 1.5:1. As another example, if Y = 1.620-inch and X = 1.010-inch, ratio would be 1.6039:1.
What happens when you increase rocker arm ratio? The distance from the rocker arm pivot to the roller valve tip does not change. This is a “fixed” distance referred to as the pivot length in order to suit the specific cylinder head, since we can’t change the location of the valve stem. When ratio is increased, the distance from the rocker arm pivot to the pushrod adjuster cup (X) is the dimension that changes, decreasing the length of the “X” dimension. This slightly changes the angle of the pushrod, moving the upper end of the pushrod, outboard, closer to the valve spring.
Increasing rocker arm ratio is a simple means of increasing effective valve lift. By knowing the camshaft’s lobe lift, we multiply lobe lift by rocker arm ratio to determine effective valve lift. If the lobe lift on the cam is, say, .432-inch, using a smallblock Chevy standard arm ratio of 1.5:1, .432-inch X 1.5 = .648-inch valve lift. If we increase arm ratio to 1.6:1, by multiplying .432-inch X 1.6:1, we increase valve lift to .6912-inch. So, rather than changing the cam, we can “cheat” by changing to a higher ratio rocker arm.
You can also determine the change in lift by referring to the cam’s published valve lift. Divide the known valve lift by the existing rocker arm ratio, which will reveal the camshaft’s lobe lift. Then multiply the lobe lift by the proposed higher rocker arm ratio to determine the new valve lift. For example, if the known valve lift is .500-inch and the existing rocker arms have a ratio of 1.5, .500 divided by 1.5 shows a cam lobe lift of .333-inch. If you’re considering moving to a 1.6:1 rocker arm, multiple the .333 lobe lift by 1.6, which results in a new valve lift of .5328-inch.
The majority of aftermarket performance roller rocker arms are stamped or laser etched to identify the ratio, so there’s no need to actually measure the rocker arm (although hand measuring the arm’s two pivot distances using a dial caliper will allow you to obtain an approximate ratio).
Instead of opting for a higher lift camshaft, increasing rocker arm ratio allows you to obtain a greater valve lift. However, there are other factors to consider. Since the higher ratio rocker arm will be longer, you potentially run the risk of increased valve guide wear if you don’t pay attention to pushrod length. Altering arm ratio will potentially require a different pushrod length, or the rocker arm may need to be raised or lowered to achieve proper geometry, so as with any valvetrain setup, it’s important to measure for proper pushrod length. Never assume pushrod length. Always measure, rather than assuming that a “stock” pushrod length will provide correct geometry. Another element to consider is the valve spring. Since the higher ratio rocker arm will open the valves further, you may need to upgrade to stiffer valve springs or springs that provide additional coil clearance in order to avoid spring bind under full lift, since an increase in rocker arm ratio will compress the spring further during the full valve open event.
Aluminum rockers tend to feature more substantial mass as opposed to steel rockers in order to provide the needed strength. If you’re changing from stock type rockers to a fatter aluminum rocker, you may run into rocker arm-to-valve-cover clearance issues, making it necessary to carefully check for clearances during test fitting. Chances are, if you already have beefy aftermarket lifters and already have adequate valve cover clearance but are simply changing ratios, you likely won’t have an issue in terms of valve cover clearance.
While roller-tipped rocker arms induce less friction at the valve stem tip, attention must be paid to the valve material. If valves are made of a softer valve material such as titanium, a harder surface is required at the valve tip to avoid high spring pressure forcing the rocker arm wheel from digging into the valve. While some titanium valves feature a hard coating, common practice involves the use of hard steel lash caps. Lash caps are available in various thicknesses to also allow fine-tuning of pushrod length. If lash caps are to be installed, they must be in place during pushrod length measuring.
When determining pushrod length, as well as shaft-mounted rockers that feature bolt-on stands, install light checking springs, paint the valve tips (or lash caps) with a marker and slowly rotate the crank and cam, turning the crank a full 360-degrees. Remove the rockers and inspect the witness mark made by the roller tip, which is the rocker sweep pattern. The witness mark should be narrow and centered on the valve tip. If the mark is biased towards the intake side of the head, the pushrod is too short or the rocker arm stand needs to be lowered. If the witness mark is biased towards the exhaust side, the pushrod is too long, or the rocker arm stand needs to be raised using shims. On shaft-mount rocker systems that feature a mounting stand, rocker stand height will influence the rocker arm to valve sweep location.
ROLLER LIFTERS
The use of roller camshafts and lifters reduces lobe contact friction and allows the use of more aggressive camshafts, as well as eliminating the concern of flat-tappet cam break-in issues. The obvious advantage lies in the reduced friction between the lifters and cam lobes. A flat-tappet lifter rubs against the cam lobe, while a roller lifter glides across the lobe as the roller wheel rotates. In terms of camshaft “break-in,” while a flat tappet cam requires a specific break-in period in order to allow the lifters to properly rotate in their bores in order to mate the two surfaces and avoid a “dig-in” of the lobe to lifter, a roller lifter setup essentially requires no time consuming break-in period, providing the lifter is properly lubricated. While we’re on the subject of lubrication, be sure to pay attention to the lifter maker’s oil recommendations, as some manufacturers specify a certain viscosity based on their lifter design. Some makers, depending on the specific lifter model, may recommend the use of 5W-20, 5W-30 or 10W-30, etc., and to avoid anything heavier than 40W. Just pay attention to their recommendations before selecting the oil. Lighter viscosity oil may be needed to suit smaller oil passages and tighter clearance tolerances.
However, the frictional reduction that rollers offer is only one aspect of the advantage that roller cams and lifters offer. Roller lifters provide increased acceleration and lifter velocity. Because a roller lifter doesn’t dig into the lobe during operation, the cam lobe lift curve can be broader without the need to increase lift or the need to increase duration.
It’s common for today’s aftermarket engine blocks to feature taller lifter bores as compared to OE blocks. Using a standard-height lifter may require notching the lifter bore for pushrod clearance. To address this, aftermarket lifter manufacturers such as Jesel, Crower, Crane, Comp, Morel, Isky, etc. offer .300-inch taller lifters to accommodate this, eliminating the need to notch the top of the lifter bores.
Some roller lifters are designed with a series of needle bearings that provide the rotational performance of the roller wheel, while some lifters feature a specially formulated high-hardness bronze alloy bushing. The reason that some lifter makers now offer bronze bushed wheels is to eliminate the potential catastrophic damage that might occur if the needle bearings were to break loose. This type of failure can send needle bearings scattered through the engine. Any failure of the roller wheel’s location can destroy the camshaft in quick order. Whether you opt for lifters that feature needle bearings or bushings, sticking with established manufacturers that have a track record of making components that provide performance and endurance is key. As with any critical engine component, if you plan on pounding the engine, avoid bargain-basement roller lifters.
When dealing with cylinder heads that feature shallower valve angles than the traditional 23-degree angle, rocker arms often require an offset to accommodate the relocated valves due to both angle and increased valve diameter. As a result, lifter pushrod cups often need to feature an offset in order to provide proper rocker-to-pushrod-to-lifter alignment. Offset pushrod cups feature the cup moved from the center of the lifter to 180-degrees right or left, depending on the individual cylinder location. Offset lifter pairs may feature a centered cup at the exhaust lifter and an offset cup at the intake lifter, or offsets at both lifters. Various combinations are available to suit specific aftermarket cylinder heads.
Today’s roller lifters are offered with a variety of body and roller wheel diameters. For small block Chevy applications for example, commonly available body diameters include “standard” .842-inch, .847-inch, .903-inch, .904-inch, etc. Lifter diameters can vary among manufacturers. Regardless of whether you plan to use an OE block or aftermarket block, it’s critical to measure lifter bores, and to correct as needed, to achieve proper oil clearance for the specific lifters that you select. Always adhere to the lifter maker’s clearance specifications, but in general terms, oil clearances of 0.0015-0.0018-inch are recommended. Don’t assume any dimensions. Regardless of the lifter printed specs, measure the lifter body diameters before performing milling or honing of lifter bores.
Roller lifter wheels are offered in a range of diameters, in the range of .700-inch all the way up to a whopping 1.220-inch. A larger diameter roller rotates slower and reduces the loads needed to open the valvetrain. You may have to adjust your cam specs when using a larger diameter roller due to an increase in duration. A larger diameter roller may allow you to get more aggressive with your opening ramp design. You should discuss your planned lifters’ roller wheel diameter with your cam supplier in order to obtain the proper lobe design.
A range of roller lifter designs have been designed over the years, each with its own characteristics and advantages. First of all, we need to understand that by design, a roller lifter must not be allowed to rotate within its bore, in order to keep the roller wheel aligned with the cam lobe. While a flat tappet lifter is designed to rotate in its bore during operation in order to prevent the lifter from digging into the lobe, a roller lifter must be guided in a fixed vertical plane to allow the roller wheel to rotate without “skidding” across the lobe. Several designs exist to accomplish this. An OEM design may feature individual lifters that feature opposing flat spots on the lifter body. In order to keep the lifters guided in plane, a “double dogbone” plate captures a pair of lifters, serving as a guide. The plate, somewhat resembling a double-ended open-end wrench, features flat internal surfaces that guide the flats on the lifter. The dogbones are held in place by a tempered sheet metal brace that is bolted to the block’s lifter valley, with fingers that hold down the center of each dogbone.
One of the very common approaches with aftermarket roller lifters involves a pair of lifters that are connected by a pivoting link bar, or “tie bar.” The bar holds the pair of lifters in plane, preventing each lifter from rotating in their bores. The link bars pivot on each lifter, allowing freedom of vertical lifter movement. The link bar length is designed to accommodate the engine style (SBC, BBC, etc.) in terms of lifter bore to bore spacing.
More recently developed designs include “keyed” lifters that require special bronze bushings. The bushings, which are interference-fit to the parent bores, feature a male key (usually located in-line with the roller axle, 90-degrees from the roller wheel rotational plane) that rides in a milled groove slot in the bronze bushing. This style requires no link bar, since the keys maintain roller lifter alignment relative to the cam lobes. Naturally, the bronze bushings must be installed to the engine block to locate the vertical grooves in order to place the lifter roller wheels in plane with the cam lobes. This style eliminates the weight of the link bars, reducing valvetrain reciprocating mass. Manufacturers such as Jesel offer a special keyway bushing installer tool to achieve correct bushing keyway position/alignment.
Another innovative design is the “cartridge” style roller lifter. This unique approach features a bronze guide and lifter system that is easily serviceable, even at trackside. Instead of a press-fit bronze guide, the parent bore is opened to accept a drop-in 1.312-inch O.D. bushing. The bushing is secured to the block with an aluminum collet and a single screw. The collet engages to the outside of the bushing with a fine thread that allows for bushing height location in increments of 0.0125-inch. Once height is established, a set screw prevents the installed bushing location from changing. The 1.000-inch diameter lifter drops into the bushing, guided by channels machined into the bushing. The distinct advantage of this style is its ease of service, since the bushings are easily removable when needed, for block cleaning, bushing wear or in the rare event of a lifter failure, eliminating the need to remove a press-in bushing and reinstall and hone a new bushing. To cite Jesel’s cartridge roller lifters as an example, these lifters also feature a large 1.220-inch roller wheel, which reduces the pressure angle of the lifter.
Read this article with all images in the digital issue of Engine Professional magazine https://engineprofessional.com/2025EPQ3/#p=36