Hydraulic roller lifters are new alternatives to the traditional mechanical lifter, and are considered by some car experts to produce less car noise and less chance of problems.
When you operate a hydraulic lifter, the engine pushes
down on the camshaft. The camshaft in turn exerts pressure on the lifter, and
particularly a small plunger attached to a metal spring. At the same time, oil
travels to the lifter, and pressure within it causes the plunger to move