The cam lobes actuate which engine components?

• A. Valves
• B. Crankcase
• C. Pistons
• D. Oil pump

Answer: (A)

Cam lobes are designed to open and close the engine valves by converting rotational motion into the vertical motion that lifts valve stems. As the camshaft turns, each lobe pushes on a lifter (or follower/rocker arm) so the valve rises against its spring to admit air-fuel mixture or exhaust, and then the spring closes it once the lobe passes. This precise timing controls when the valves open and for how long.

The other components don’t get actuated by the cam lobes. The crankcase simply houses oil and the engine parts; pistons move up and down because of the connecting rods driven by the crankshaft; the oil pump is driven by the crankshaft or timing gears and serves lubrication, not valve actuation.