Top of piston travel called?

• A. Mid-stroke
• B. Idle position
• C. Top dead center (TDC)
• D. Bottom dead center (BDC)

Answer: (C)

The highest point the piston reaches inside the cylinder is called Top Dead Center. "Dead center" means the piston is momentarily at a fixed point and changes direction there, so it isn’t moving as it finishes one stroke and starts the next. At this top position, the combustion chamber is smallest (clearance volume), and ignition timing is coordinated with this point for efficient combustion. The bottommost point is Bottom Dead Center, while mid-stroke is simply the middle of the travel, and idle position isn’t a standard term for piston extremes. In four-stroke engines, you can have Top Dead Center on the compression stroke and again on the exhaust stroke, but in any case, the topmost position is the Top Dead Center.