What position is the pistons when at top dead center?

At top dead center (TDC), the piston is at its highest point in the cylinder, positioned at the very top of its stroke. This occurs at the end of the compression stroke for the intake or compression cycle, and at the end of the power stroke for the exhaust cycle in a four-stroke engine. At this position, the piston is effectively at the zero-degree mark in relation to the crankshaft. It is crucial for timing events in the engine's operation, such as valve opening and closing.