All About Cylinder Heads and How They Work
Getting a Head Start
Your cylinder head or heads are located, as you might expect, at the top of your engine. Inline or straight engines have one cylinder head, while V-shaped engines and boxer engines have two, one for each bank of cylinders. Cylinder heads are usually made of cast iron or aluminum. Many of the moving parts that make your engine work are found inside the cylinder head. It houses the intake and exhaust valves, rocker arms, and the spark plugs . In engines with overhead cams (OHC), the camshafts are inside the cylinder head. The cylinder head also contains inlets that allow coolant from the radiator and oil to flow through the engine. Depending on the design of your engine, the layout of your cylinder head will differ from other cylinder heads. The material can also differ. If all of this info has got your "head" spinning, don't worry; we'll walk you through how the cylinder head works, and all the different kinds of cylinder heads out there.
What Is a Cylinder Head, Exactly, and How Does It Work?
The cylinder head is where a great deal of the action for running your engine happens. It contains the combustion chambers where the quick burn of fuel and air that moves the pistons occurs. For this to take place, the cylinder head must be connected to the intake and exhaust manifolds . The intake manifold feeds air into the head through the intake ports, past the intake valves and into the combustion chamber. Once the air and fuel have been combusted, exhaust gasses exit the combustion chamber past the exhaust valves, through the exhaust ports, to the exhaust manifold. The intake and exhaust valves are located inside the cylinder head. These allow fresh fuel and air to enter, and combusted exhaust gasses to exit the chamber, respectively. These must be precisely timed to open and close at the right times to keep the engine running smoothly. This is achieved through a system of parts known as the valvetrain.
In the early days of automotive engineering, flathead or sidevalve engines were the norm. In these, valves are on the side of the combustion chamber, in the engine block, and fuel and air enter from the side and exhaust exits out the same side. A cross section of this type of combustion chamber looks like an upside down letter L. So, flatheads are sometimes known as L-head engines. The valves in a flathead engine are operated directly by the camshaft. This made flatheads easy to produce and to work on. They also were very reliable. A flathead engine could still run with a broken valve.
Intake Over Exhaust Engines
Intake over exhaust engines represent a further improvement over the flathead design and the first time that valves were positioned in the cylinder head. The exhaust valve remained in the block, while the intake valve was located in the cylinder head. In early examples, the intake valve was operated by suction from the chambers. Later versions used mechanical valvetrains to operate the intake valves. The camshaft moves push rods that push rocker arms that operate the valves. Although intake over exhaust was more common, some exhaust over intake engines were built. Intake over exhaust engines can still be found in some motorcycles.
Overhead Valve Engines
Overhead valve engines pick up where the intake over exhaust engine left off, by putting both the intake and exhaust valves in the cylinder head. The camshaft is located in the block, or between the V in V configuration engines. Because of this, they are sometimes called cam-in-block engines. The cam can be driven by the crankshaft via a short chain or belt or even directly by a gear. Like in the intake over exhaust engine, push rods push rocker arms to open and close the valves.
Overhead Camshaft Engines
Overhead camshaft engines are technically still overhead valve engines. The valves remain in the cylinder head. Rather than using push rods to connect the camshaft to the valves, though, the camshaft or camshafts are moved to a position above the valves, where they can activate the valves directly. The camshaft is connected to the crankshaft by a belt or a chain known as the timing belt or timing chain.
Has That Thing Got a Hemi?
Another factor of cylinder head design that can affect the performance of an engine is the shape of the combustion chambers. The shape of the combustion chamber can affect how completely the air fuel mixture burns and how well gasses flow through the engine. The shape affects the placement of the valves and spark plug, as well.
Cylinder heads are usually made of one of two materials, cast iron or aluminum. Iron cylinder heads are easier to produce and less expensive, but they are heavier than aluminum heads. Aluminum cylinder heads, in addition to being lighter, also dissipate heat better which makes engine overheating less likely. In some engines, an aluminum head sits atop a cast iron engine block. One disadvantage of this design is that the two metals expand at different rates when heated. That puts a strain between the two parts which lead to cracking or warping of the cylinder head.
Get Your Head Checked
As mentioned above, the most prevalent problem with cylinder heads is that they can crack or warp. Since combustion occurs inside them, they are exposed to high heat. Of course, they have coolant flowing through them, but coolant leaks and other cooling problems may cause the engine to overheat. Overheating makes the metal of the engine expand. When the cylinder head and the engine block are made of different metals, the different metals expand at different rates, which put strain on that metal. That can lead to cracks or warping in the cylinder head.
Do-It-Yourself Head Transplants
Although an experienced do-it-yourselfer could replace a cylinder head, this might be a job you'd prefer to leave to the professionals. We would not advise that you attempt replacing your cylinder head without having a lot of prior mechanical experience. Improper installation could lead to serious damage to the engine and necessitate even bigger repairs.
Need a New Cylinder Head Replacement?
If you are in need of a cylinder head replacement, you have come to the right place. 1A Auto not only knows everything about car and truck cylinder heads, but we stock the highest quality, best fitting aftermarket cylinder heads available. We carry cylinder heads constructed of different materials for a selection of vehicles, and at great prices!