Which component is not part of the cylinder head?

The water pump is not part of the cylinder head, but instead, it is typically located in the engine block or an associated accessory drive system. The primary function of the water pump is to circulate coolant throughout the engine's cooling system to maintain an optimal operating temperature.

On the other hand, the cylinder head houses essential components critical to the engine's operation. Fuel injectors are positioned in or near the cylinder head to deliver fuel directly into the combustion chamber for efficient combustion. The camshaft, which is responsible for opening and closing the engine's valves, is often integrated into or mounted on the cylinder head, especially in overhead camshaft designs. Valve train components, such as the valves, rocker arms, and springs, are directly located in the cylinder head, allowing for precise control of air-fuel intake and exhaust processes.

Thus, the correct choice is the water pump, as it serves a different role outside the context of the cylinder head.