What component pushes against the valve tappets to facilitate their movement?

The component that pushes against the valve tappets to facilitate their movement is the cam lobes. In an engine, the camshaft is responsible for controlling the opening and closing of the valves, which are critical for the intake of air-fuel mixture and exhaust of combustion gases. The cam lobes, which are shaped to lift the tappets upward in a precise manner, rotate in synchrony with the crankshaft, transforming rotational motion into linear movement. This action is essential for the proper timing of the engine cycle and ensures that the valves operate in harmony with the pistons.

Other components mentioned have different functions; for instance, piston rings serve to seal the combustion chamber and control oil consumption, while connecting rods link the pistons to the crankshaft, converting the up-and-down motion of the pistons into rotating motion. The crankshaft’s role is to turn the linear motion of the pistons into rotational energy, but it does not directly influence the operation of the valve tappets. Thus, cam lobes are specifically designed to engage with and move the tappets, making them the correct answer in this context.