Cam lobe

An eccentric used to change rotary motion into linear motion. The valve operating cams used in a reciprocating engine are eccentrics made onto the cam shaft.  /  An eccentric, or lobe, on a rotating shaft that changes rotary motion into linear motion. A cam, or lobe, on the cam shaft of a reciprocating engine opens the intake and exhaust valves at the proper time relative to the position of the piston in the cylinder.These eccentrics are enlarged portions of the cam shaft that rotate about a center different from the shaft's center. The cam followers that operate the valves ride on the cam lobes, and as the cam shaft rotates, the cam lobes move the cam followers up and down in a direction perpendicular to the axis of the cam shaft.