Final answer:
An engine can alter valve opening and closing independent of crankshaft rotation through the use of a camshaft.
Step-by-step explanation:
An engine can alter valve opening and closing independent of crankshaft rotation. This is achieved through the use of a camshaft. The camshaft is a rotating shaft that has lobes or cams which push against the valve lifters. As the camshaft rotates, the lobes or cams lift the valve lifters, which in turn open and close the valves. The rotation of the camshaft is typically driven by the crankshaft through a timing belt or timing chain.