One complete movement of the piston in one direction requires ____________ of the engine crankshaft:

• A. One-half revolution
• B. One revolution
• C. Two revolutions
• D. Four revolutions

Answer: (A)

A single stroke of the piston in one direction happens with a 180-degree turn of the crankshaft. As the crankshaft rotates halfway (one-half revolution), the piston travels from one extreme position (top dead center) to the opposite extreme (bottom dead center) in that direction. To return and move in the opposite direction, another 180 degrees are needed. In a four-stroke engine, the full engine cycle spans two crank revolutions, but each individual piston movement in one direction is just half a revolution. That’s why the correct amount is one-half revolution.