Hydraulic roller lifters are relatively new additions to the lifter family and are steadily increasing in popularity. These lifters are often used in high-performance applications, as they are often the only type of lifter capable of handling the steep profiles of high-performance camshafts. However, hydraulic roller lifters do offer benefits when used in any type of engine. An understanding of how hydraulic roller lifters work must begin with some basic knowledge about lifters in general, particularly what the purpose of a lifter is and the components with which a lifter is composed of.
Lifters are cylindrical metal pieces located on the top of each lobe on the camshaft. As the camshaft turns within the engine, the lifters convert the energy produced by the camshaft's lobes into a lifting motion. A single pushrod is located on top of each lifter. As the lifter rises, so too does the pushrod. The pushrod actuates a rocker arm, which in turn opens a valve within the cylinder head.
A hydraulic lifter has a spring inside it. A metal plunger sits on top of this spring. On top of the plunger is a thin metal shield, upon which a round piece called a pushrod seat covers. The pushrod seat is what the bottom of the pushrod rests on top of. A single snap ring is inserted into the lifter just above the pushrod seat to keep the entire assembly together. Roller lifters also feature a metal ball at the base of the lifter. Each pair of roller lifters are connected together with a metal bracket, which prevents the lifters from rotating in their bores.
The most important, and most recognizable, component of hydraulic roller lifters is the ball located at the base of the lifter. Lifters that do not feature this ball generate a tremendous amount of friction as the camshaft's lobe scrapes against the base of the lifter. The rotating ball of hydraulic roller lifters substantially reduces this friction because the ball spins as the camshaft twists. Oil is fed into the lifter from the engine block. The pressure produced by the oil forces the plunger within the lifter upward. The valve spring within the cylinder head that moves along with the lifter pushes down on the plunger. These competing forces allow the plunger to act as a shock absorber, thereby minimizing the shock produced by the valvetrain.
Solid lifters require periodic adjustment, which can only be done after the valve covers have been removed, and are notorious for being noisy at low engine speeds due to the shocks produced by the valvetrain. By contrast, hydraulic roller lifters are relatively quiet, as they absorb this shock. Nor do hydraulic roller lifters require periodic adjustment. The most significant benefit from roller lifters, however, is their ability to work well with aggressive camshaft profiles, meaning camshafts that feature lobes that open the valves within the cylinder heads a greater distance. Therefore, hydraulic roller lifters are typically used only in high-performance applications that use these more aggressive camshafts.
