How does a cylinder head work and what does it do ?

Educational

Apr 11th, 2019

How does a cylinder head work and what does it do ?

Positioned right on top of a vehicle's engine block is the cylinder head. It is the cylinder head that houses components like the intake valves, as well as, exhaust valves. Also, you will find springs & lifters, as well as, the combustion chamber. Here, we will be considering the different cylinder head designs and how they function. 

The cylinder head is made up of passages which facilitate the flow of air and fuel in the cylinder and, also, allows the outflow of exhaust gases. The cylinder head passages are referred to as ports or tracts. Then again, the cylinder head is responsible for creating a channel for the coolant to get to the engine block which helps to cool the components of the engine. It makes use of a gasket which helps to prevent the leakage of water or oil inside combustion chambers. 

Cast iron is used to make a lot of OEM cylinder heads. This helps improve its durability, and it is much more affordable. The downside of cast-iron, however, is that it is quite heavy and not very efficient when it comes to the dissipation of heat. There are manufacturers that rather make use of aluminum cylinder heads which happen to be a lot lighter when compared to cast-iron. Aluminum cylinder heads are usually used in performance, as well as, race cars.

Vehicles that have inline engines come with just one cylinder head while vehicles that have V engines come with double cylinder heads which serve each individual cylinder bank. There are cars where you will find the cylinder banks positioned very near a V engine and this will require just one cylinder. In very large industrial automobiles, you will likely notice that each cylinder has its own head. This helps to reduce the cost of replacing cylinder heads. 


KINDS OF CYLINDER HEADS

Cylinder heads come in different types which determine how they function.

Flathead Cylinder Head

The very first cylinder head types. They don’t have any moving parts and only provide protection for the cylinder block. For the flathead, the flow of air is inefficient and leads to the engine performing poorly.

Overhead Valve Cylinder Heads

Basically superior when compared to the flathead cylinder head. The camshafts are located above them with their pushrods, as well as, valves connected in order to ensure that the airflow is smooth and efficient.

Overhead Camshaft Cylinder Head

A very advanced cylinder head design. You will find the camshaft position right inside the head which means that there is no need for pushrods. The air flow is much better and makes the engine a lot more efficient.


HOW THE CYLINDER HEAD WORKS

In this section, you will get to understand everything that has to do with how a cylinder head works. Most of the activities that help your engine to run relate to the cylinder head. Here, you will find the combustion chambers, and it is in the chambers that the fuel and oil which is channeled into the piston get a quick burn. In order for this to happen, there must be a connection between the cylinder head and the intake & exhaust manifolds.

The head receives air from the intake manifold via its intake ports, down to the intake valves and all the way into its combustion chamber. As soon as fuel and air combustion have taken place, the exhaust gases in the combustion chamber leave through the exhaust valves and go right through the exhaust port all the way down to the exhaust manifold. In the cylinder head, you will find intake, as well as, exhaust valves. They are responsible for the entrance of new fuel and air. Also, they allow exhaust gasses to leave. There is a need for precise timing for the opening and closure of the valves in order to ensure that the engine continues to run smoothly. The valve train is responsible for ensuring that this is possible. 

A valve train is made up of various parts that are peculiar to different engine layouts. Apart from the intake and exhaust valves, a valve train can comprise rocker arms, a single camshaft or even double camshafts. It is the responsibility of the rocker arms to exert pressure on the valves for them to be opened or closed. Pushrods get to move them as a response to the camshaft that you find in the block. There are certain engines where the camshaft is positioned right on top of the valves so that they can be opened directly. So, the head and valve train configuration are what determines the components, as well as, the way in which they will function. Now, let us consider how the cylinder head works for different configurations -


Flathead Engine

When automotive engineering was still in its infant years, it was normal for flathead engines or side valve engines to be used. Here, the valves are positioned on the combustion chamber’s side which is located in the engine block. The entrance of fuel and air take place from its side with exhaust gases going out the same way. If you take a cross-sectional view of its combustion chamber, it has an L shape that is placed upside down. This is why flatheads happen to be referred to as L-head engines. The camshaft is responsible for the operation of the valves in this kind of engine. This is the reason that flatheads are relatively very easy to manufacture and carry out maintenance work on. Also, they have a very high level of reliability, and even if the valve is broken, the engine could still work.

Engines that have the flathead design have some flaws. The speed of the engine is limited due to the circuitous path that exhaust gases must pass through in order to exit the combustion chamber, thus, causing a rise in temperature. Today, newer designs of engines have been invented as a solution to these issues and have become more widely used than the flathead engines. At first, most of these new engines were only derived from the side valve design. 

When it comes to T-head engines, the entrance of fuel and air inside the combustion chamber take place from one side with exhaust gases exiting from the other side. T-head engines have a cross-sectional view that is shaped like a T. This causes the gases to have a cross flow that lets the engine breathe better. Camshafts are directly used to operate the valves but, this time, double camshafts are used as one performs the function of the intake while the other performs the function of the exhaust. Today, side valve engines do not happen to be the most effective, but you will find them in farm equipment, as well as, simple machinery based on the fact that they are simple and reliable.


Intake Over Exhaust Engine

This is basically an innovation with respect to the flat head design. It is with this type of engine that we began to see the cylinder head containing valves. While the block contains the exhaust valve, the cylinder head contains the intake valve. Earlier, you would find that combustion chambers suction was responsible for operating the intake valve. Later, mechanical valve trains were responsible for operating the intake valves. Pushrods are moved by the camshaft and exert pressure on the rocker arms which in turn operate the device. Even if this kind of engine happened to the common, a reverse design was developed which is the exhaust over intake engine. However, today, in some motorcycles, you’ll find the intake over exhaust engine.


Overhead Valve Engines

This kind of engine is an improvement on intake over exhaust engines. Here, you will find the valves for intake, as well as, exhaust positioned inside the cylinder head. In the block, you will find the camshaft, and for engines that have a V configuration, the camshaft is positioned between the V. This is the reason that they are, also, referred to as cam-in-block engines. There are two ways in which the cam can be operated. This can be done with the use of the gear or by the crankshaft with the help of a belt. The valves are opened and closed with the use of rocker arms that are pushed by the pushrods.

Today, overhead camshaft engines have begun to replace overhead valve engines, but there are still lots of advantages which make the overhead valve engine to continue being used. Mostly, General Motors are strongly linked with this kind of engine design. Since the cam is located in the engine block, it results in the reduction in the entire engine size. Also, it is relatively easier to manufacture. One very significant disadvantage of this kind of engine design is the fact that it comes with a lot more valve train components which imply that there will be increased valvetrain inertia, thus, causing a reduction in engine revolutions every minute. Then again, this engine design is known to be noisier since a lot of parts move.


Overhead Camshaft Engines

In a way, we can liken overhead camshaft engines to overhead valve engines. Here, you will find the valves in the cylinder head. However, full pushrods are not used as a way of connecting camshaft and valves. Rather, the camshafts are elevated above the valves which means that they can directly operate the valves. Then, a belt is used to connect the camshaft and crankshaft. A chain could also be used, and they're both referred to as timing belts and timing chains. In some engines, only 1 camshaft is used for the operation of the intake valves, as well as, the exhaust valves. However, in other engines, each valve set comes with its own distinct camshaft. Basically, they are referred to as single overhead cam, as well as, dual overhead cam engines for 1 camshaft and double camshaft engines respectively. 

Even if these kinds of engines happen to have a higher complexity in contrast with overhead valve engines and are larger in size, they have their own advantages too. The elevation of the camshaft to a position above the valves helps designers to be more flexible in the placing of the valves. Therefore, this improves the valve timing precision while allowing for more than one port to be used for a cylinder. Although these engines happen to be very complex, you get to experience very high efficiency and effectiveness. 


ISSUES WITH CYLINDER HEADS

A very significant problem that is mostly associated with cylinder heads is that they get to crack very often when the engine overheats. When a cylinder head cracks, it will lead to the leakage of the coolant which will, in turn, causes inefficiencies in the cooling of the engine. First, the overheating condition of the affected engine will continue to increase. Then again, with cracks in the cylinder head, oil will begin to leak and find its way inside the combustion chambers. The oil leakage can cause significant damage to the engine which will lead to the need for repairs that are very expensive. There are cases, however, where engine replacement is the only solution. Another way to know that the cylinder head of an engine is bad is if the engine begins to perform poorly or misfires.

As a vehicle begins to overheat, most drivers have the tendency to refill the radiator with water rather than taking steps to determine what exactly caused the overheating. This eventually leads to the cracking of the cylinder head with the addition of water which causes the temperature to change rapidly. One way to reduce the possibility of your vehicle overheating is to ensure that you always keep your radiator in top condition and fill it with water. Then again, ensure that the cap is always sealed tightly. Carry out checks to ensure that the thermostat of the engine remains in top shape and correctly reflects the engine's temperature. There must be no belts that are stretched, as well as, hoses that are leaky. The fan, also, must be in top working condition. In the event that you experience an overheating situation, stop driving the vehicle and kill the engine. Leave it until it gets cooled totally before you go ahead to add water. 

If there are hot spots that are localized in the vehicle’s engine, it can cause the cylinder head to crack. Localized hot spots are a signal that the cooling system does not work efficiently. Take steps to detect hot spots and ensure that they are adequately addressed, especially, if you noticed a failure in the head gasket in recent times. When engine components do not expand evenly, it can lead to hot spots. Also, leaky hoses can lead to localized hot spots.

So, if you experience car overheating, ensure that you get the cylinder head, as well as, the gasket checked in order to detect cracks or warps. If cylinder head wrapping has occurred, it can lead to cylinder head cracking. What you need to do in this case is to replace the head gasket and take steps to evenly ground the head to avoid cracks.