The four-stroke cycle engine begins with which piston position?

• A. Top dead center
• B. Bottom dead center
• C. Mid-stroke
• D. Neutral position

Answer: (A)

In a four-stroke engine, the cycle is defined from the piston at the top of its travel. This top-dead-center position marks the boundary after the exhaust stroke and just before the intake stroke begins. From this point, the piston moves downward to bottom dead center to draw in air and fuel, then upward to compress it, followed by the power stroke, and finally the exhaust stroke back to top again. Bottom dead center is simply the farthest downward point of travel, not the starting point of the cycle, and mid-stroke or neutral aren’t standard reference points for beginning the cycle.