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.