Cylinder Heads
For many of us, who use cars simply as a means of transportation, car terminology can be a vast, impossible to navigate forest. What is horsepower and what do horses have to do with cars anyway? What is a transmission and what does it do? What the heck does RPM stand for? To make matters worse, sometimes automotive terminology can be confusing. What is the difference between and engine and a motor? Aren’t they the same. (They’re not, as a matter of fact!) Another bit of confusing automotive technology is the cylinders and cylinder heads. We generally know that cars that feature more cylinders generally go faster and have more power, but what does all that mean?
For starters, cylinders are the central working parts of an internal combustion engine. They are the areas in which the auto’s pistons travel. Multiple cylinders (can you guess what they look like?) are often arranged together, side by side, near the back of the engine block. The cylinder head, then, is the part of the engine that sits above the cylinders. The cylinder head is a platform. It is also where the car’s valves and spark plugs are located and it contains a part of the car’s combustion chamber.
There are different types of engines, so it stands to reason that there are also different types of cylinder heads. For example, in a type of engine called a flathead engine, the mechanical parts of the valve train are all located within the car’s engine block. So a cylinder head in a flathead engine is simply a flat plate of metal which is bolted to the top of the aforementioned cylinder bank. The head gasket lies somewhere between the cylinder head and the cylinder bank. Many mechanics like this type of cylinder head arrangement. They find it easy to repair because it is so easy to get into the engine and access the individual parts. Though cars no longer use flathead engines (for the most part), flathead engines were used in earlier models of automobiles. They are also still frequently used in machinery with small engines, such as lawnmowers. Flathead engines are generally no longer used for cars because of performance issues. Because they required incoming air to flow through a complex and convoluted path, they did not allow for the high performance that we expect from our cars these days.
Because flathead engines did not allow for high performance, car makers switched to the overhead valve engine design. In this type of engine, the top half of the cylinder head contains different parts, including the camshaft in an overhead cam engine or, in other types of engines, whatever mechanism is used to transfer rotational mechanics from the crankshaft in order to operate the valves. In the overhead valve engine design, the cylinder head is filled with passages, called ports, so that a fuel and air mixture can pass through it and travel from the intake manifold to the inlet valves or for exhaust gases to travel from the car’s exhaust valves to the exhaust manifold. The ports are also used for antifreeze to do its job and cool the cylinder head and engine.
Just as cars have multiple cylinders, they also often have more than one cylinder head. While a straight engine may probably only have one, a V engine (i.e. you will have heard of the V engine as V6, V8, etc.) usually has two cylinder heads. Because the engine is V shaped, the engine will usually have one cylinder head at each end of the V shape. Sometimes, though, V engines may only have one cylinder head.