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.