Cylinder Heads and Camshafts

The air flows from the intake manifold into the intake ports of the cylinder head, which is the assembly at the top part of the cylinder. The cylinder head has an arrangement of valves that open to allow the air from the ports into the cylinders. Normal engines use poppet valves here, which are metal circles attached to long stems. The circle fits into a circular area of the cylinder port and moves downward on its stem to open and let the air into the cylinder. These valves are held closed by valve springs, and pushed open by a device called a camshaft. Since the camshaft must spin in sync with the pistons to make sure the valves open and close at the right time, most engines use a belt, chain, or system of gears ...

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