Which component transforms the rotary motion of the crankshaft into up-and-down motion?

The correct answer is the piston. The piston is a crucial component within the engine that performs the action of translating the rotary motion of the crankshaft into linear, up-and-down motion.

When the crankshaft rotates, it moves connecting rods that are attached to the pistons. As the crankshaft turns, the motion of the connecting rods pushes the pistons up and down within the cylinder. This up-and-down motion is essential for the combustion process, as it creates the pressure that drives the engine's power stroke and ultimately propels the vehicle.

While the camshaft, engine block, and cylinder are integral to the overall function of an engine, they do not perform the specific role of converting rotary motion into linear motion. The camshaft primarily controls the timing of the valve openings and closings to allow for efficient air and fuel intake as well as exhaust expulsion. The engine block houses the cylinders and provides structural support for the engine, and the cylinder itself is where the pistons reside and move vertically. However, it is the piston that is directly responsible for the up-and-down motion resulting from the crankshaft's rotation.