How to Blueprint Engines: Rocker Arms Guide • Muscle Car DIY (2024)

Cam timing events are transmitted to the lifter, pushrod, rocker arm, and then the valve. You need strong rocker arms for particular applications, so the valves are precisely actuated. Rocker arms are installed on all overhead-valve engines and transmit lifter movement to the valves. Because the rocker arm is essentially a lever, the length of the rocker (its pushrod contact point to pivot), increases valve lift relative to cam lobe lift. In other words, the rocker’s length provides a ratio-multiplier that magnifies the lift of the cam lobe to create increased valve lift.

This tech tip is from the full book, MODERN ENGINE BLUEPRINTING TECHNIQUES: A PRACTICAL GUIDE TO PRECISION ENGINE BUILDING.

For a comprehensive guide on this entire subject you can visit this link: LEARN MORE ABOUT THIS BOOK HERE

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The rocker arm lock nut is properly tightened down and then valve lash will be measured.

Rocker Arm Ratio

Determining gross valve lift involves considering both the camshaft lobe lift and the rocker arm ratio. The ratio of the rocker arm (length of fulcrum) increases the effective valve lift beyond just the camshaft’s lobe lift. Here’s the formula:

Gross Valve Lift = cam lobe lift x rocker arm ratio

For example, if a camshaft’s intake lobe lift is .365 inch and a rocker arm ratio of 1.6:1 is used, the formula works out like this:

Gross Valve Lift = .365 x 1.6 .584-inch gross lift

If you’re considering changing the rocker arm ratio and you know what the gross lift is and what your current rockerarm ratio is, here’s a simple formula to calculate current lobe lift:

Current Lobe Lift = current gross valve lift ÷ current rocker arm ratio

During test fitting, verify that the rocker tip is centered to the valvestem tip. If you’re using pushrod guideplates, the guideplates may require adjustment for positioning.

For example, if your current gross valve lift is .600 inch and you’re currently using 1.5:1 rockers:

Current Lobe Lift = .600 ÷ 1.5

.400-inch lobe lift

Now that you know what the cam lobe lift is, multiply that by the rocker arm ratio that you plan to use. That gives you the new gross lift.

New Gross Valve Lift = lobe lift x new ratio

For example, let’s say that you’re considering moving from a 1.5:1 rocker to a 1.6:1 rocker, using the same camshaft. The formula works out like this:

New Gross Valve Lift = .400 x 1.6

.640-inch new gross lift

As a rule, each ratio increase (in whole numbers) adds about .035 inch of increased valve lift. Changing from 1.5:1 rockers to 1.6:1 rockers increases valve lift by about .035 inch. This provides increased valve lift and quicker valve opening and closing rates. Although this sounds great, before you rush to a higher rocker arm ratio, be aware of the following:

Increasing rocker arm ratio decreases piston-to-valve clearance, so you need to check this.
Valvespring retainer-to-valveguide clearance must be checked, as this clearance decreases.
Check for valvespring bind at full lift.
Longer pushrods are likely required with high-ratio arms, so make a careful pushrod length determination. You are measuring for precise pushrod length anyway.

As you know, rocker arm ratio refers to the distance between the centerline of the rocker arm pivot to the center of the pushrod cup. The higher the ratio, the shorter this distance becomes. Unfortunately, most published OEM rocker arm ratios cannot be trusted. Due to mass-production tolerances, the listed ratios are theoretical.

For instance, a set of OEM rockers that are listed as having a 1.5:1 ratio might actually involve a range of, say, 1.49 to 1.54:1. For high-precision fulcrum lengths and superior consistency, the performance aftermarket is the way to go. High-quality aftermarket performance rockers are produced with a much higher level of precision and consistency. Increasing rocker arm ratio is a neat way to increase power. You get the effect of a high-lift cam without the need to increase duration. The valve is opened faster, lifted farther off its seat, and closed later.

Guideplates

Stud-mounted rocker arms allow the rockers to pivot around the axis of the stud; shaft-mounted rockers maintain a constant rocker alignment. Studmounted rockers require some type of guiding or alignment to prevent the pushrods from walking around. Depending on the cylinder head design, closer tolerance pushrod slots in the head or steel guideplates take care of this.

Guide plates have pushrod slots. The slots must be checked for edge burrs (deburred if necessary). During test fitting, slowly rotate the crank and check each pushrod for depth clearance at its guideplate slot (primarily at max lift). Especially when using a high-lift cam and/or highratio rocker arms, you may need to deepen the slots, but do not widen the slots.

If your head requires guideplates, you must use hardened pushrods to prevent pushrod galling. Most guideplates are stamped from steel and may have sharp burrs around the pushrod slots. Be sure to inspect each guideplate and deburr any sharp edges before installing them.

Rocker arms with higher than stock ratios locate the pushrod cup closer to the rocker arm’s central pivot point. During test fitting, closely check for pushrod-to-guideplate-slot clearance at maximum lift. Although aftermarket performance guideplates usually have longer slots for this reason, but you still need to check this clearance. If you lengthen (deepen) the pushrod slots, be careful to only make the slots deeper. Don’t oversize their width.

Also check for pushrod clearance in the heads; a high-ratio arm moves the pushrods from the original intended location in the head. If you need additional clearance at the cylinder head’s pushrod slots, you can do this with a hand-held grinder (with the head off the block). Don’t get too carried away. A clearance of around .010 inch is adequate. Removing too much material can be dangerous and may open-up a hole in an intake runner.

When installing guideplates, with the rocker studs finger tightened in place and with rockers and pushrods installed, you should be able to wiggle the guideplate from front to rear (in relation to the engine) in order to center the pushrods in the width of the guideplate slots (guideplate mounting holes usually allow a bit of movement and adjustment). Once the slots are centered to their pushrods, fully tighten the plates (using the rocker studs).

A full-roller rocker has a needle-bearing trunnion for the pivot point and a roller bearing for valve tip contact.

Roller Rockers

A stock OEM rocker arm (in most cases) rubs on the valve tip and pivots on a ball fulcrum, causing friction. A fullroller rocker arm has a needle bearing trunnion (the pivot) and a roller bearing at the rocker nose that contacts the valve tip. This virtually eliminates frictional losses. Less friction results in quicker response, freer revving, and potentially more horsepower.

Aftermarket roller rockers are also available with a roller bearing at the nose but an OEM-type pivot, and some OEM rockers are available with a needle bearing trunnion pivot but a non-roller tip. A full-roller rocker is a good choice for any application. However, using full-roller rockers becomes more important when dealing with small-diameter valvestems and/or high lift and spring pressures.

If you run 5/16-inch-diameter or smaller valvestems with high lift and high spring pressures, having a roller bearing at the nose dramatically reduces the chance of valve deflection. Also, because of the larger arc imposed on the rocker due to a high-lift cam, roller tips greatly reduce the chance for valve tip damage. If cost isn’t a factor, go to full-roller rockers.

Full-roller rockers made from forged aluminum billets that are CNC machined provide lighter weight and high strength. Pictured here is a set from Harland-Sharp for the GM LS engine.

Shaft-Mounted Rockers

Shaft-mounted rocker designs are available for most applications (depending on cylinder head design). They pivot on a common shaft instead of individually on rocker studs or bolts. The advantage of a shaft mount involves improved valvetrain stability. When shaft mounted, the rockers can’t individually move around the axis of the valve, so rocker-to-valve and rocker-to-pushrod stability and consistent contact is improved.

Performance rockers made from steel forgings offer superior full-roller performance and strength that far surpasses OEM designs.

Racing applications commonly require high strength and reduced weight. These steel Mohawk roller rockers from Jesel are a good example. Notice that weight has been shaved where possible, while retaining strength for use with high valvespring pressures. (Photo Courtesy Jesel)

Depending on the cylinder head application, shaft-mounted roller rockers are available in which each pair of a cylinder’s rockers ride on their own common shaft, rather than a full-length common shaft.

Bridged roller rockers (as on this Pontiac 455, equipped with Harland Sharp rockers) feature each adjacent pair of rockers pivoting on a common shaft. This keeps each pair of rockers in alignment, preventing them from moving out of plane relative to the valves and pushrods.

Rockers that feature a full-length common shaft mount are often adjustable, allowing you to fine-tune each rocker’s location for proper valve alignment.

Spacer shims are placed between rocker-to-stand locations and between rocker-to-barrel spacers. Barrel-type spacers provide spacing between rockers.

Adjusting shaft-mounted rockers (where a common full length shaft is featured) can be a time-consuming process in order to position each rocker’s roller tip centered to each valve. Chances are you won’t achieve alignment on the first try. To re-adjust, use a caliper to measure the required change, disassemble the shaft, reinstall the shims, and try again. It’s not that difficult, but it takes patience.

This Jesel shaft-mounted roller rocker system (for use with Dart Big Chief II big-block Chevy heads) includes rockers, rocker stands, and a stand-height checker. Due to the offset valve design of this Dart head, Jesel developed a unique rocker system that requires a special setup.

With valvespring removed, the stand height checker drops over the valve stem, while the opposite end rides on a checker shaft that rests in the rocker stand shaft groove. The checker allows you to dial in correct rocker arm geometry. The valve stem tip should be flush with the upper surface of the checker. If the valve tip is lower (below flush with the checker), correction means moving to longer valves or milling the head’s shaft stand bosses. A quicker, easier, and cheaper fix is to use the proper-thickness valve lash cap. If you’re using titanium valves that don’t already have hard tips, you need lash caps anyway. If the valve tip sits too high (above flush with the checker), shimming the rocker shaft stands is required.

This tech tip is from the full book, MODERN ENGINE BLUEPRINTING TECHNIQUES: A PRACTICAL GUIDE TO PRECISION ENGINE BUILDING.

For a comprehensive guide on this entire subject you can visit this link: LEARN MORE ABOUT THIS BOOK HERE

Left-to-right while using the Jesel checker: valve too high, valve flush and correct, valve too low. (Illustration Courtesy Jesel)

The Jesel rocker system for the Dart Big Chief II race head is a good example of how a unique design is sometimes required. Occasionally different shapes or offset rockers are needed to accommodate a unique valve layout or angle design. Because of the requirements of this particular head, the Jesel system has three different rocker arm designs: a straight arm with a 90-degree shaft position for two of each head’s intakes, a straight arm with an off-angle shaft position for all exhaust locations, and an offset intake arm (two per head).

Initially tighten rocker arm adjustment to zero lash with the cam on its base circle.

For hydraulic lifter applications, with the cam on its base circle, and after initially setting to zero lash, tighten the adjuster by no more than 1/2 turn, then lock the adjuster with its jam nut.

Break-In and Adjustment for Roller Rockers

Granted, there’s no frictional issues with a full-roller rocker at the valve and at the pivot/trunnion, but make sure you apply moly lube to the pushrod-to-rocker contact (to each upper end of the pushrod and to the contact, cup, or ball at the rocker). Rocker manufacturers include a high-pressure lube in the kit or they recommend a specific lube.

It’s highly advisable to soak all roller rockers in a tub of clean, 30-weight engine oil for at least 1/2 hour before installing (I usually soak mine overnight). This allows oil to penetrate into the needle bearings and bearing axles.

With pushrods and rockers installed, hand-rotate the crank through two full revolutions, then remove the rocker.

Adjust valve lash according to the cam manufacturer’s instructions where solid lifters are used (whether roller or flat-tappet). For hydraulic lifter setups with roller rockers, place the cam on its base circle (where the lifter is at its lowest point) and gently adjust the rocker to achieve zero lash, then tighten the adjuster by 1/2 turn (this provides a small amount of preload to the hydraulic lifter).

Even if you’ve already measured and checked for proper pushrod length, it’s a good idea to perform a final check. With the rocker removed, paint the valvestem tip with a black marker. Install the rocker, adjust lash, and rotate the crank 2 full turns. Remove the rocker and check the witness mark on the valve tip. It should be at the center of the valve. If the mark is biased toward the intake side, the pushrod is too short. If the mark is biased toward the exhaust side, the pushrod is too long.

Rocker Arm Materials

Rocker arms may be stamped steel, ductile iron, investment cast steel, aluminum forgings, extrusions, machined billet aluminum, or powdered metal. These material choices are for OEM as well as performance aftermarket arms.

If a 100-point restoration is the goal, you likely want to use whatever type was originally installed (likely stamped steel, ductile iron, cast aluminum, or steel forgings). If you have a late-model LS engine, you may opt to stick with PM rockers. However, for upgrades with power and durability in mind, you want to reduce friction and increase rocker strength, and you want rockers with correct and consistent arm ratio. This means upgrading to high-quality aftermarket rockers that are made of investment-cast steel, forged steel, forged aluminum, extruded aluminum, or billet aluminum.

Because steel is generally stronger than aluminum, and depending on how radical the build is and the anticipated spring loads and high-RPM use, steel may be a better choice in certain applications. But there are various opinions. The best thing to do is to talk to the rocker arm manufacturer for a recommendation.

OHC setups use cam followers that directly transmit valve action from the cam lobes.

Both types of materials are used in high-output racing engines. Sometimes it boils down to race sanctioning body rules or simply on how much you want to spend. From an expense standpoint, from less money to more, ductile iron, cast aluminum, forged aluminum, and steel rockers are your choices.

PM rockers are in common use by many OEMs (the GM LS engines are an example). Although the OEM trunnion/ bearing design is poor (see page 142 for more details), the PM construction is surprisingly good. Generally, PM rockers are okay up to about 400 hp. Beyond that, I don’t even consider them.

OHC Followers

Overhead cam (OHC) engines don’t have pushrods that connect lifter movement to rocker arms. Instead, cam “followers” provide a direct leverage connection from the valve tips to the lifters or cam lobes to the valve tips (depending on design). For a high-performance or race application, aftermarket upgraded followers, which have roller contact (instead of friction/sliding contact) at both the valves and lifters, are available. Just as in roller rocker upgrades on overhead valve (OHV) applications, roller cam followers greatly reduce frictional losses and allow for higher and more consistent engine revs.

Valve Cover Clearance

Nice big, beefy aluminum roller rockers may provide the performance and durability that you desire, but remember that dimensionally larger rockers may not clear OEM valve covers. Since most custom engine builds are likely fitted with aftermarket valve covers (which are readily available in taller heights), this really isn’t an obstacle, but consider this clearance in order to decide if you need taller covers.

A simple way to determine this is to place a cover onto the head, with no bolts. While a buddy slowly rotates the crank by hand, place your hand on top of the valve cover. If rockers begin to contact the cover, you can feel the cover bump up. If so, you need taller valve covers. Before you invest in a pair of spiffy valve covers, test rocker clearance using a spare cover with the same height of the ones that you’re considering.

Upgrading OEM LS Rocker Arm Trunnions

The GM Generation-3 and -4 LS engine platform provides a quantum leap beyond the earlier small-block Chevy engine. Overall, it’s a great design with plenty of horsepower potential and good durability. However, a notable weakness involves the rocker arm. The majority of OEM LS-platform engines have PM rocker arms, which are surprisingly strong and well suited for street operation. The downside involves the trunnion and needle bearing system.

Under high loads and high engine speeds, the cageless bearing outer housings can work their way out of their bores, allowing the needle bearings to work their way out of the bore and scatter into the engine. There’s no guarantee that this failure will occur, but especially with an upgrade to a high-lift cam and stiffer springs, the potential for the failure increases. If you find one or more mystery needle bearing during a routine oil change, it is clear evidence that at least one rocker arm is losing its trunnion bearings.

For performance use, get rid of the OEM powdered metal trunnion and the cheap uncaged bearings in favor of a durable aftermarket trunnion kit upgrade. This is an OEM setup. Notice the small bearing needles? How’d you like to have a bunch of these floating through your engine? Seriously, if you plan to stand on an LS engine with OEM rockers once in a while, you need to upgrade the trunnions and bearings!

If you plan to retain the factory PM rockers, a simple and inexpensive fix is to perform a trunnion bearing upgrade using a readily available kit.

Comp Cams, as an example, offers a high-quality trunnion bearing upgrade kit (PN 13702-KIT). This kit, applicable to LS1/LS2/LS3/LS6/LS7 OEM rockers (as well as iron-block versions such as LQ9, etc.), includes new trunnions, new caged and prelubed bearing assemblies, circlips, and rocker arm mounting sockethead cap screws (along with two thick, installation-assist washers). The new trunnions have extended tips with circlip grooves. Instead of the bearing housings relying on a press fit, the additional circlips serve to prevent possible bearing assembly walk-out.

These bearings aren’t going anywhere, so the rocker bearing issue is no longer a concern. The new trunnions and bearings are also made of high-quality materials and are designed to withstand high RPM and high spring pressures. An upgrade kit replaces the cageless OEM needle bearing assemblies and PM trunnions with very high strength, premium 8620 steel-alloy trunnions and fully caged roller bearings for vastly improved durability.

The trunnion-bearing swap procedure can be handled using a bench vise or hydraulic press with appropriate-size inserts or with a specialty tool designed for use with a bench vise. An example is Summit Racing’s tool (P/N SME-906011), which makes this job easy.

Trunnion Upgrade Procedure

Before beginning, clean the rockers with solvent or in a hot tank. After removing the original bearings and trunnions, you have the option of additional surface finishing, by having the rockers tumbled in a media tumbler or by a light blasting with glass bead, soda, walnut shell, etc. Avoid dwelling the blasting pressure in the trunnion bores, valve contact tips, or pushrod cups, and do not run a reamer through the trunnion bores. Do not sand blast; it is far too aggressive.

Place the tool vise fixture onto one jaw of a bench vise. Place the OEM rocker into the fixture’s V-saddle.

Align the (black) presser to the OEM bearing, with the counterbored end of the presser facing the bearing. Tighten the bench vise to press-out both OEM bearings and the trunnion (needles fall out). Inspect and clean the rockers as needed.

Place the presser onto the short end of the Summit kit’s mandrel. Slide a new bearing onto the long end of the mandrel (make sure that the stamped symbols on the bearing faces the mandrel’s flange). Slip the aluminum alignment sleeve onto the long end of the mandrel, seated against the bearing.

Summit Racing’s new trunnion vise tool (PN SME-906011) allows you to easily and safely remove the original bearings and trunnions and install the upgraded Comp Cams trunnion kit using a common bench vise instead of a hydraulic press. Removing old trunnions and bearings and installing the new Comp Cams upgrade kit in all 16 rockers can be done in as little as 30 to 45 minutes without breaking a sweat.

The Comp upgrade kit has high-strength steel trunnions, caged bearings, and peace-of-mind circlips. This setup will never allow bearing needles to fall out. The Comp upgrade kit also includes a pair of thick steel washers that are used during the press-fit of the new bearings.

Slide the mandrel assembly into the rocker arm bearing bore (the aluminum alignment sleeve enters the bore first to align to the rocker body).

Using a bench vise, press the bearing into the rocker body until the mandrel’s flange bottoms-out onto the rocker body. Perform this single-bearing installation to all 16 rockers before proceeding with trunnion and opposite-side bearing installation.

Place the rocker arm body onto the Summit vise fixture, with the previously installed bearing facing the fixture.

Slide the new trunnion halfway into the bearing bore (leaving the outside end of the trunnion exposed to align the remaining bearing). Apply engine oil to the outside of the bearing. Slip the remaining bearing onto the exposed trunnion (make sure that the stamped symbols on the bearing cage face outward).

Place the kit’s thick steel washer onto the end of the trunnion (against the bearing face). Tighten the bench vise until the washer bottoms-out against the rocker body

Verify that the trunnion rotates freely, and that a slight amount of endplay (side to side) exists, in the range of .004 to .008 inch. If you don’t have any endplay, adjust the bearing depth accordingly. Using snap-ring pliers, install one circlip to each end of the trunnion. Verify that the clip is fully seated in the trunnion clip groove.

Install the upgraded rocker arms to the cylinder heads using the new socket head cap screws supplied in the Comp Cams kit. Be sure to rotate the trunnion so that the flat recess side of the trunnion’s bolt hole faces upward (the socket head cap screw must seat against this recessed flat side of the hole). Tighten the cap screw to 22 ft-lbs, following the OEM installation procedure.

Install the new upgrade kit using a press or rocker arm vise tool. It’s critical to smoothly draw the OEM bearings out and draw the new bearings in. Do not try to bang the old trunnions out or attempt to install the new bearings with a hammer.

During assembly, the kit’s washers provide positive stops during the press-in of the bearings.

Using the Summit kit’s presser (black piece) push the bearings and trunnion out of the rocker. The presser has a shallow counterbore that aligns with the stock bearing. Summit’s specialty fixture is shown on a bench vise. Push the old trunnion completely out of the rocker along with both OEM bearings.

Using the Summit kit’s mandrel, place the new bearing onto the mandrel and then the aluminum alignment sleeve. This aligns the new bearing with the rocker arm body. Push a new caged bearing into one side of the rocker.

Insert the new trunnion so that one end engages the newly installed bearing. With the new trunnion in place, insert the next bearing onto the trunnion (it slips on). Make sure that all bearings are installed with the stamped lettering side facing outward!

Here the second bearing is in place on the trunnion.

Place one of the kit’s washers over the exposed end of the trunnion, against the outer face of the new bearing.

Using a bench vise with Summit’s specialty fixture to secure the opposite side, press the remaining bearing into the rocker, so that the outer face of the bearing is flush with the outer surface of the rocker body. Apply a bit of engine oil to the outside of the new bearings to ease press-in.

Before installing the circlips, verify that the trunnion rotates freely and that a small amount of endplay is present (.004- to .008-inch endplay). Using snap-ring pliers, install one circlip onto each end of the trunnion. Rotate the trunnion and inspect to verify that each circlip is fully seated.

This overhead view shows a fully assembled rocker with Comp’s trunnion upgrade. Note that one side of the trunnionmounting hole is recessed, that is, countersunk with a flat surface. This recessed side of the hole must face upward during rocker installation; the opposite side of the trunnion is round, to seat onto the rocker stanchion.

Depending on the version of your LS cylinder heads, some have integral rocker pedestals while others require separate pedestal rails. This 5.3L LS has rocker rails. Hand-snug a couple of rocker bolts to center the rail before fully tightening. Also, be sure to apply high-pressure assembly lube to all valve tips, rocker pushrod cups, and rocker valve tips.

If using aftermarket ported cylinder heads, check to see if the intake rocker boltholes are open to the intake runners. If so, apply thread sealant to the intake rocker bolt threads. OEM head intake rocker boltholes are generally not open to the runners.

Written by Mike Mavrigian and posted with permission of CarTech Books