When someone talks about his en-gine, or about an engine that heplans to build or buy, the termroller is sometimes bandied about,often with some level of vagueness.When used loosely, roller can refer

to either the style of camshaft or to the rocker arms, orboth. Let’s clarify.

A roller camshaft features lifters that are equippedwith a roller bearing that rolls against the cam lobe. Bycomparison, a flat-tappet camshaft features lifters that

rub against the cam lobes. Flat-tappet lifters are designedto rotate in their bores in order to continually spread theload around the lifter face. If the lifter can’t rotate, fric-tional wear concentrated across one path would cause thelifter/lobe to wear prematurely.

A flat-tappet cam’s lobes are slightly tapered to pro-mote lifter rotation. Roller cams feature a nontaperedlobe surface. Because the lifter bearings roll across thecam lobes, this virtually eliminates any lifter-to-lobe fric-tion and/or wear issue. Also, roller cam lobes and rollerlifters can handle much more abrupt transitions as the

20 October 2013

CAMS, LIFTERS& ROCKERS

Roller cams, roller lifters and roller rockers each provide value to aperformance engine builder. They’re all part of an engine’s valvetrain, but

their functions are complementary rather than interchangeable.

The illustration on the left above is an example of a roller cam lobe. Because the lifter features a rollerbearing that rolls along the lobe as opposed to rubbing, cam makers can provide more innovative loberamp angles. The right illustration is an example of a flat-tappet cam lobe. It features a narrower peak.

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ON A ROLL(ER):

BYJIMGIBSON

lifter runs from the cam lobe basecircle onto the lobe ramp and ontothe lobe peak, which results in thelifter remaining at maximum lift for alonger period of time.

So, in addition to eliminating scuffwear, roller camshafts generally offerperformance advantages as opposedto flat-tappet cams. However, de-pending on the application, and con-sidering today’s advancements invalvetrain stability, flat-tappet camdesigns can compete head-to-headfrom a sheer horsepower standpoint.In other words, we shouldn’t blindlyassume that a roller cam will alwaysprovide more horsepower. But whenyou consider the reduced frictionalfactor and valve timing control of-fered by roller designs, for the street,a roller cam upgrade will usually pro-vide superior performance. When weconsider racing applications, thereare too many variables that come intoplay to make blanket statements.

Since there’s no wear pattern es-tablished on a roller cam betweenlobes and lifters, you can mix uproller lifter positions, or replace onelifter at a time during future service.Because a flat-tappet cam establishesan individual wear pattern betweeneach lobe and its lifter, when servic-

ing (removing lifters and/or cam), ifyou plan to use the original lifters,they must be reinstalled in the origi-nal positions relative to the block’slifter bores and the same camshaft.Otherwise, you’ll need to buy a com-plete set of new lifters to use with theexisting cam.

Another aspect (and distinct ad-vantage) of a roller camshaft system is

the near elimination of a worrisomecamshaft break-in period. Flat-tappet(solid or hydraulic) lifters must bewear-mated to each respectivecamshaft lobe. During break-in, theflat-tappet lifters must be allowed to

22 October 2013

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This illustration shows why a flat-tappet lifter cannot be used with aroller cam design. The edges of the lifter will dig into the lobe, destroyingboth cam and lifter. There’s no digging in with a roller tappet.

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Roller camshafts require theuse of roller lifters. A largeroller bearing is secured with aheavy-duty trunion.

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features a roller bearing that ridesalong the cam lobe, the lifter cannotbe allowed to rotate in its bore, inorder to keep the bearing in planewith the cam lobe. This is why allroller lifters must feature a type of“guide” design that prevents lifterbody rotation. In the case of OEroller lifter designs, this might in-volve two opposing flats machinedon the lifter body, which register in-to a separate dogbone guide that’ssecured in the lifter valley; or in thecase of current-generation GM LSengines, for example, the lifters fea-

24 October 2013

rotate in their bores. This is accom-plished via a slight crown (convex)surface of the lifter face and a slighttapered angle of the cam lobe thatforces the lifter to rotate.

Even though a flat-tappet lifter’sface may look completely flat to thenaked eye, a slight convex shape(crown) is machined to the lifterface to accommodate the neededlifter rotation. Depending on thespecific application, this convexcrown may be as little as .0009 in. toas much as .015 in. in height. With aroller cam system, since each lifter

Since a roller lifter must be held in plane with the cam lobe (to result in aconstant rolling footprint for the roller bearing), roller lifters must notbe allowed to rotate in their bores. One method of preventing this rota-tion is to bridge an adjacent pair of lifters together. The bridge pivots oneach lifter, allowing each lifter to travel through its bore freely.

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Circle #22

The photo on the left shows an OEM rocker arm for an LS engine.While the pivot features a trunion and bearing, the valve tip is non-roller and rubs as it rides on the valve stem tip. If stock LS rockerarms are to be used in a performance application, it’s imperative toupgrade the trunions and bearings with an aftermarket kit, as thestock needle bearings are not caged securely and can pop loose. Onthe right is the same rocker arm, cleaned up and upgraded withComp Cams’ trunion kit. Superior bearings and cages, a heavy-dutytrunion and lock clips eliminate the worry of bearing failure. If youplan to use the stock LS rockers, you must perform this upgrade.

25October 2013

ture machined flats at the top of thelifter body that register into ashared plastic lifter bucket.

Performance aftermarket rollerlifters are offered as direct OE re-placements; they’re also offeredbridged, where two adjacent liftersare connected together by a pivotingcrossbar, which prevents the pair oflifters from rotating without theneed for additional guides. Rollercam break-in is still a consideration(especially when high valve springpressures are used), but breaking ina roller cam is not nearly as criticalas it is with a flat-tappet cam.

Roller RockersRoller rockers, while offering re-duced friction operation comparedto conventional rocker arms thatpivot on a ball, with direct frictionalrub at the valve tip, are not auto-matically required with the use of aroller camshaft setup.

In other words, an engine canfeature a roller camshaft combinedwith ball friction rollers, or withroller rockers. Or, an engine mightfeature roller rockers but not aroller cam. The two don’t necessari-ly need to be used together. Rollercamshafts and lifters can be used inan engine that features nonroller

rockers; by the same token, rollerrocker arms can be used in an en-gine that features a flat-tappet solidor hydraulic camshaft.

Taking advantage of roller bear-ings in both valvetrain areas (camlifters and rockers) reduces operat-ing friction. Whenever you can re-place a rub-together design withone that features roller bearings,you reduce friction, which in turnreduces drag, which frees up horse-power and engine speed and re-duces operating heat.

There are also two versions ofroller rockers. Rocker arms areavailable that feature roller pivots(trunions and bearings) but non-roller tips. Rocker arms are alsoavailable that feature a full-rollerdesign, with both roller bearing piv-ots and roller tips at the valve end.

An example of a roller-pivot rock-er arm that features a nonrollervalve tip are the original equipmentrocker arms used in GM’s LS seriesof engines. These rockers pivot on atrunion bar that’s equipped withneedle bearings. However, at thecontact point between the rockerarm and valve, the rocker tip rubsagainst the valve, with no rollerbearing. An example of a full-rollerrocker arm is Harland Sharp’s LS

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continued on page 26

A full-roller rocker arm (above left) features a heavy-dutytrunion axle and roller bearing for smooth gliding across thevalve tip. This reduces operating heat and power-robbing fric-tional losses. It virtually eliminates frictional issues, with theexception of the pushrod contact (right). Oil ports in the rock-er arm deliver oil to the pivot bearings and the tip bearing.

rocker arm that features a heavy-duty trunion and heavy-duty cagedbearings at the pivot point, as wellas a roller bearing at the valve tip.Full-roller rockers also are offeredby other performance aftermarketmanufacturers, such as CompCams, Trick Flow, Crane Cams,Scorpion, Jesel and Lunati, to namea few.

Is it wise to replace OE rockerswith full-roller rocker arms? Theanswer, depending on one’s budget,is always yes. Any engine’s valve-train would be enhanced by the useof full-roller rocker arms. Full-roller rockers generally cost morethan nonroller rockers or OE pivot-only roller rockers. Depending onthe level of durability (street vs. ex-otic race applications), full-rollerrockers can range from affordableto extreme.

Roller rockers are also availablein different materials and forms ofconstruction, ranging from cast andpowdered metal, to forged or billetsteel, to forged or billet aluminum.Powdered metal is popular amongOE rockers, while forged or billetmaterials provide increasedstrength and (depending on materi-al and design) weight savings forquicker valve operation.

Overhead-cam (nonpushrod) en-gines also may be upgraded withroller cam followers, offered by var-ious aftermarket manufacturers.These feature a roller bearing thatrolls against the cam lobes, as op-posed to nonroller followers thatrub against the lobes.

To sum up, an engine may beequipped with a roller camshaft, re-gardless of the style of rocker arm.By the same token, pivot-roller orfull-roller rocker arms may be usedregardless of camshaft design. Orroller camshafts and roller rockersmay be used in combination. Al-though functionally related, theroller issue is independent regard-ing cams or rockers.

26 October 2013

Circle #24

To maintainprecise rockerarm lateralgeometry,lateral pivotingmust be elimi-nated. Oneapproach is tobridge a pair ofrocker armstogether by acommon axle.This ensuresthat the rollertips will remaincentered ontheir valves, andsignificantly reduces poten-tial pushrod deflection.