The concept of placing a small wheel at the end of a tappet to reduce friction has existed for decades, and in fact, roller camshaft setups have been available for the American V-8 engines we tinker with since the early '50s. Yet for some reason, most rodders consider roller cam technology to be a relatively recent development. True, the roller cam has evolved over the years, but the basic design and the advantages it offers remain the same. The additional benefit of time has also helped to reduce the cost of roller setups somewhat, bringing them more in line with the budget of the average enthusiast, so that today, obtaining this technology and all it has to offer is relatively simple, so long as you know what has to be done and what parts are needed to accompany a roller setup. You'll also have to decide what type of roller you're looking for: solid, hydraulic, or factory-style hydraulic. We'll look at the basics and then break it down into the specifics of the various types of rollers.
Roller HardwareSolid roller cams were the first rollers to be used in the engines we know and love. Initially, they were only found in the fastest cars at major dragstrips, but like most bits of performance technology, in time roller cams trickled down to the enthusiast level. Later, hydraulic versions of the roller became available, first from the OE manufacturers and then from the aftermarket. Roller cams must be ground on specific blanks, usually made from hardened or billet steel rather than the cast iron typically used with flat-tappet cams. Although the roller tappets are intended to reduce friction, the rollers themselves place higher loads on the lobes since the actual contact patch between the two is smaller than that of a flat tappet setup. This load is then intensified by the fast opening rates, higher valvespring pressures, and extra tappet weight.
Since wheels are used on the tappets, they obviously have to be aligned with the cam lobes, so some form of retainer is required to keep the lifters from rotating in their bores. Aftermarket roller cams-usually referred to as retro-fit roller cams these days to differentiate them from factory-style rollers-usually use tie-bars linking pairs of lifters. The bar keeps the lifters aligned while also providing enough movement for them to ride up and down independently.
With the exception of having a wheel, the tappets themselves operate much like flat tappets, though they are specifically machined to align with the host engine's oiling holes in applications where oil must be pumped through the pushrods to lubricate the rest of the valvetrain. Roller tappets-particularly hydraulic versions-are usually taller than their flat tappet counterparts, and this extra height is accommodated by the pushrods, which are made shorter to compensate.
The higher loads associated with roller cams also mean that higher-grade timing sets must be employed with these systems. Usually, this means a double-roller-type chain and sprockets. For factory-style rollers, a specific timing set is often required to properly interface with the snout of the camshaft. Retaining the cam also becomes an issue with roller setups. Most flat-tappet cam lobes are machined to provide a slight rearward thrust to keep the cam seated in the block, but this can't be built-in to roller cams, so an additional retaining device must be used. In retro-fit applications where a cam retaining plate can't be bolted in place, a cam "button" is employed. A cam button is a small hub that fits into the center of the timing gear, which then places mild tension against the timing cover, keeping the cam seated.
It should also be noted that roller cams often require specific fuel-pump pushrods to cope with the harder steel material of the cam itself. For similar reasons, the distributor gear must also be made from a material compatible with the steel of the camshaft-bronze is often the material of choice. Many factory roller cams have iron distributor gears to allow standard distributor gears to be used (see sidebar for more info).
Although the use of a roller lifter does reduce friction between the lifter and lobe, roller setups can impart greater stress on other related valvetrain components, like the valvesprings, pushrods, and retainers. Quick opening and closing rates require premium-quality springs to "keep up," warding off valve float for maximum power. However, the valvesprings are heavily taxed by radical roller profiles that slam the valve up off its seat and then drop it back down just as suddenly. This isn't really an issue on factory-type roller setups, at least when using stock or even mild performance grinds, but racing roller valvetrains typically go through springs and retainers faster than comparable flat tappet setups. Despite this, many racers consider the increased cost of roller valvetrains a small price to pay for the increased performance they provide.
Solid RollersLike mechanical flat tappet cams, solid roller valvetrains need precise adjustment and periodic re-adjustment, though many using roller cams claim that valvetrain adjustments are required far less frequently than with flat-tappet arrangements, probably as a result of decreased wear between the tappet and cam lobe. Of all the roller setups, the solid roller is the toughest on the rest of the valvetrain. The quick ramps coupled with a lack of any cushioning between the cam lobe and valve can result in a harsh environment when radical profiles are used. But again, racers using these setups typically view this as an acceptable trade-off for increased performance, particularly since race engines don't see the prolonged use that street engines do. For the ultimate in high-performance valvetrains, the solid roller is king.
Retrofit Hydraulic RollersAftermarket hydraulic roller cams are similar to their solid-roller counterparts, using the same camshafts in some cases and having pairs of lifters linked with slotted tie-bars. Of course, the main difference is in the body of the lifter, which incorporates a chamber to be filled with oil, just like a hydraulic flat-tappet. The oil-filled chamber provides some cushioning for the rest of the valvetrain, absorbing clearances to quell mechanical noise and taking up slack when other parts of the valvetrain wear. Hydraulic rollers combine the performance benefits of a roller setup with the low-maintenance features of a hydraulic valvetrain to provide relatively quiet, trouble-free performance for regularly driven vehicles.
Factory Hydraulic RollersAs mentioned previously, the auto manufacturers began using roller cams back in the '80s to take advantage of the high-lift/short-duration profiles that flat-tappets can't accommodate, allowing manufacturers to increase performance without sacrificing idle quality, low-rpm torque, or emissions output.
All of the Big Three's roller setups are hydraulic, though they are quite different than aftermarket setups. To accommodate these systems, most manufacturers designed specific engine blocks, usually with taller lifter bores that are topped with machined-flat pads. The lifters remain individual, and are aligned with small guides-often bone-shaped-which fit into flat areas machined into the lifter bodies. The lifter valleys of these blocks are also cast and/or machined with bosses to hold a guide retainer "spider" that applies pressure to the lifter guides.
Like aftermarket rollers, factory roller cams are made from high-grade steel, and in fact, are often machined from billet stock. Also like aftermarket setups, high-quality double-roller timing sets are often used, along with bolt-on camshaft retainer plates. Chevy roller cams are stepped at the snout to interface with the retainer plate, while Ford small-blocks, which use retainer plates even for flat-tappet applications, have the step machined into the cam gear.
Cross-BreedingThere is a certain amount of parts-swapping that can be done to mix and match roller cam components. Since factory roller cams are steel, as are most aftermarket rollers, the factory roller lifters are generally compatible with aftermarket cams, and vice versa. However, factory roller lifters are limited in the amount of lift they can handle by the flats machined into the lifter bodies. If the lifter is raised too far in its bore, the bottom of the flat will contact the lifter guide. Still, the factory setups can handle a fair amount of lift. Retro-fit roller lifters can be used in factory roller blocks as well, or on factory-style roller cams in non-roller blocks. However, when a factory roller is used in a non-roller block, extra attention must be paid to ensure that the cam is retained, and that it will not be pushed back too far (by a cam button or other means) so that the timing set contacts the block. On older Chevy small-blocks in particular, the collar of the cam retainer plate must be used to serve as a spacer even if the retainer is not bolted on to the block. We've seen retainer plates with the bolt-ears cut off in these applications, or aftermarket Torrington bearing spacers. By the way, when a flat tappet cam is used in a Chevy roller block with a double-roller timing set, the area around the oil plugs surrounding the front cam journal may have to be ground for clearance.
The Roller AdvantageRegardless of whether your intent is to rip up the strip or just perk up your cruiser, your engine can likely realize the benefits of roller camshaft technology. Factory-built hydraulic roller engines have definitely stood the test of time, often displaying little or no wear to the camshaft after well past 100,000 miles. The higher-quality timing sets used in those engines also seem to have a significantly longer useful life than the nylon-geared single-chains of yore. But the best part is the increased performance the factory rollers provide without any sacrifices. Aftermarket solid rollers have opened up a new avenue for race-engine builders looking to squeeze every ounce of potential from their engines, while retro-fit hydraulic rollers allow the street/strip enthusiast to add roller technology to non-roller engines while maintaining quiet, low-maintenance motoring. What's the downside of roller cams? Probably just the price of admission, so start saving up and thinking about which roller will find its way into your next engine project.
Other Stuff You'll Need:* Cam retainer plate or button* Hardened, shorter pushrods* Hardened or roller fuel pump pushrod* High-performance double-roller timing set* Proper distributor gear
A Word On Distributor GearsAs we've discussed elsewhere in this article, roller cams are generally made from high-grade steel, rather than the iron used for typical flat-tappet cams. The problem this creates for the distributor drive gear, which is also usually iron in an engine that originally had an iron cam, is that the steel of the cam's drive gear will eat up the iron distributor gear in a big hurry. The simple solution might seem to be a steel distributor gear, but premature wear is again an issue, this time for both the distributor gear and the cam. Since the idea of consuming an expensive and hard-to-change roller camshaft isn't very appealing, the classic solution has been to use a bronze distributor gear, which is very soft and will bear the brunt of the wear between the cam and the distributor gears. The bronze gears are relatively cheap and easy to replace, so this compromise has been accepted for some time.
However, once roller cams began moving from the racetrack to the street, increased durability became mandatory. When Chevrolet began using factory-issue roller cams, it used a steel distributor gear to mesh with the steel billet cam. However, the distributor gears are treated with a special coating to limit wear and protect the cam. Ford roller cams also use a treated steel distributor gear. These gears seem to be compatible with aftermarket steel cams as well.
Some aftermarket roller camshafts have alternative means of coping with this issue. Comp Cams has been using ductile-iron roller camshafts for some applications that are treated to an austempering process that leaves the lobes harder than the cam's distributor drive gear, which is not treated. This permits the use of a standard iron distributor gear. Crane Cams takes a different approach by using steel roller cams with pressed-on iron distributor drive gears, again allowing iron distributor gears. Make sure you research the components you intend to use for compatibility before using them together.
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