The camshaft contains eccentrics and journals that control valve timing. Eccentrics are mechanical lobes that transfer reciprocating motion between mechanical components. Each eccentric controls one valve. For example, a four-cylinder engine that has two valves per cylinder will use a camshaft with eight eccentrics.
The shape of the eccentrics controls the finely tuned movement and timing of the valvetrain, including how far the valves lift, how long they stay lifted and when these movements occur relative to the position of the pistons.
The two main types of camshafts are flat-tappet and roller. The tappet, or lifter, on the flat-tappet camshaft is flat, and requires oil to separate its surface from the cam lobe. Flat-tappet camshafts produce high friction and high temperatures because the surfaces rapidly slide against each other. The oil film is the only barrier that prevents the lifter and the cam lobe from welding together.
Friction between the two components can eventually wear the flat-tappet cam down and affect valve operation. Engine power and efficiency will decline if the flat-tappet cams cannot lift the valves enough to adequately charge the chamber for ignition or release exhaust fumes.
The roller camshaft uses wheels, or rollers, to reduce tappet wear. The rolling element reduces virtually all friction between the tappet and cam lobe, helping extend camshaft life. Roller camshafts are generally preferred to flat-tappet camshafts because they significantly reduce wear and can enhance engine performance.
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