Which component uses a cylindrical rod with oblong lobes to operate engine valves?

• A. Piston
• B. Crankshaft
• C. Camshaft
• D. Valve stem

Answer: (C)

The component that uses a cylindrical rod with oblong lobes to operate engine valves is the camshaft. As it rotates, each cam (the oblong lobe on the shaft) pushes against a valve follower, lifter, or rocker arm, converting the shaft’s rotational motion into the vertical movement needed to open and then close a valve at the correct time in the engine cycle. This precise timing is what coordinates valve opening with piston position, enabling proper air-fuel intake and exhaust. The piston moves up and down inside the cylinder, the crankshaft turns to convert that motion into rotation, and the valve stem is the part of the valve that moves, but none of them feature the rotating rod with lobes that actively actuate the valves.