What describes the camshaft's function?

• A. A shaft that cools the engine.
• B. A shaft that supports the crankcase.
• C. A belt-driven shaft that controls cooling.
• D. An auxiliary shaft, to operate the inlet and exhaust valves at the right time, using raised lobes.

Answer: (D)

The camshaft’s job is to open and close the engine’s inlet and exhaust valves at the correct moments in the combustion cycle. It does this with raised lobes along its length; as the camshaft turns, each lobe pushes against a lifter (and then through pushrods and rocker arms) to lift a valve stem, opening the valve. When the lobe rotates past, the valve is closed by its spring. This timing is synchronized with the crankshaft so that valve events occur at the right piston positions for intake, compression, ignition, and exhaust. The camshaft isn’t about cooling or supporting the crankcase, and it isn’t a belt-driven component for cooling—its essential function is governing valve timing through the lobes that actuate the valves.