Internal combustion engines typically include a cylinder block, which houses the pistons and the cylinders through which they move, and a cylinder head to cap off the block. Certain engine configurations have multiple cylinder heads, each of which sits upon its own bank of cylinders. In some engines, such as the flathead type, the cylinder head can be very simple and designed solely to provide a sealed, removable top-end for the head. Other engines have either part of valve train, or both the valve train and the camp shaft, within the head. In either case, the cylinder head is generally mounted to the block with a graphite or metal head gasket, effectively turning the cylinders into sealed combustion chambers.
Simple engines, such as those used in lawnmowers and inline engines — like L4 and L6 units, have a single cylinder head to seal up all of the combustion chambers. Other common engines, such as the V6 and V8, contain two parallel banks of cylinders. This requires two cylinder heads, mounted in such a way to form the appearance of a V, in order to seal the cylinder block. Another type of engine that uses two cylinder heads is the flat, or boxer, engine. This configuration is similar to the V-formation in that both banks of cylinders are driven off a single crankshaft, though, in the case of the flat engine, the banks are aligned on the same horizontal plane.
The complexity of a cylinder head depends largely on the type of engine it is used in. Many older automobiles utilized what is known as a flathead engine. As the name implies, these engines used a head that was a simple, flat panel, mounted via the head gasket, to a cylinder block that itself contained the entire valve train. Cylinder heads in these applications still performed the vital function of sealing the combustion chambers, though they lacked much of the functionality found in more modern units.
Modern cylinder heads are typically used in overhead valve (OHV) or overhead cam (OHC) configurations. A cylinder head in an OHV engine generally contains valve train components, such as pushrods, poppet valves and other components that are operated by a camshaft located in the cylinder block. By contrast, OHC engines have the camshaft itself in the head, making for an even more complex unit. These types of cylinder heads usually contain the entire valve train.