Positioned right on top of a vehicle's engine block is the cylinder head.
What is a cylinder head?
A cylinder head is the part that houses components like the intake and exhaust valves. Also, you will find springs, lifters, and the combustion chamber.
It 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. The cylinder head is responsible for creating a channel for the coolant to get to the engine block which cools the components of the engine. It makes use of a gasket to prevent the leakage of water or oil inside the combustion chambers.
Most OEM cylinder heads are made of cast iron, which accounts for their durability and affordability. On the downside, cast-iron is quite heavy and not very efficient when it comes to dissipating heat. Some manufacturers use aluminum cylinder heads which are significantly lighter than cast-iron. Aluminum cylinder heads are typically used in performance cars.
Vehicles with inline engines come with one cylinder head while those with V engines come with double cylinder heads to serve each individual cylinder bank. In very large industrial automobiles, each cylinder has its own head. Using individual heads reduces 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 heads were of this type. 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
The overhead valve type is basically superior to the flathead cylinder head. The camshafts are located above them with their pushrods and valves connected 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
Most of the activities that help the engine run have something to do with the cylinder head. The combustion chambers, for instance, is where the fuel and oil get a quick burn. For this to happen, there must be a connection between the cylinder head and the intake and exhaust manifolds.
The cylinder head receives air from the intake manifold via its intake ports and down to the intake valves, where it goes all the way into the combustion chamber. As soon as combustion takes place, the exhaust gases leave the combustion chamber through the exhaust valves and go right through the exhaust port all the way down to the exhaust manifold.
The intake valves in the cylinder head allow fresh fuel and air to enter, as exhaust gases leave. The opening and closing of valves need precise timing to ensure that the engine continues to run smoothly, and this is the responsibility of the valve train.
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 of rocker arms and a single or double camshaft. The rocker arms exert pressure on the valves to make them open or close. 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 and their functions. Here is how the cylinder head works for different configurations.
Flathead Engine
When automotive engineering was still in its infant years, flathead engines or side-valve engines were typically used. For this type, the valves are positioned on the combustion chamber’s side. Fuel and air enter through the 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 are also referred to as L-head engines. The camshaft is responsible for the operation of the valves in this kind of engine.
For this reason, flatheads are relatively easy to manufacture and service. They are also highly reliable, and even when the valve is broken, the engine could still work. However, they have some flaws. Their speed 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. These flaws gave rise to the invention of other engine designs.
When it comes to T-head engines, fuel and air enter the chamber on one side while exhaust gases exit 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. While side valve engines are not considered the most effective today, they still find use in farm equipment and simple machinery due to their simplicity and reliability.
Intake-Over-Exhaust Engine
This is an innovation to the flathead design, and we began to see cylinder heads containing valves. The block contains the exhaust valve, while the cylinder head contains the intake valve. Earlier, you would find that the combustion chamber suction was responsible for operating the intake valve. Later, mechanical valve trains were responsible for operating the intake valves. The camshaft moves the pushrods, which exert pressure on the rocker arms and which in turn operate the device. A reverse design of this type of engine was developed - the exhaust-over-intake engine.
Overhead Valve Engines
This type is an improvement on the intake-over-exhaust engines. Here, you will find the valves for intake and the 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 why 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 (OHC) engines have begun to replace overhead valve (OHV) engines, but the latter remain in use, especially in GM engines. Since the cam is located in the engine block, it results in a significant reduction in engine size. One disadvantage associated with this kind of engine design is the fact that it comes with a lot more valve train components, which increases valve train inertia and reduces the engine's revolutions per minute. With more moving parts, it also tends to be noisier.
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 to connect the camshaft and valves. Instead, the camshafts are elevated above the valves which means that they can directly operate the valves. A timing belt or timing chain connects the camshaft and the crankshaft. Single overhead cam engines use only one camshaft to operate the intake and exhaust valves, while dual overhead cam engine have individual camshafts for each valve set.
The elevation of the camshaft to a position above the valves helps designers to be more flexible in the placing of the valves. It improves the precision of valve timing 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 significant problem associated with cylinder heads is that they are prone to cracking when the engine overheats. Once a cylinder head cracks, it will cause the coolant to leak, overheating will become more intense, and 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 expensive repairs. In many cases, engine replacement is the only solution. Another way to tell that the cylinder head is starting to fail is when 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, since adding water may cause abrupt changes in temperature.
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. 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 worn-out belts or leaky hoses. The fan 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 localised hot spots in the engine, it can cause the cylinder head to crack. Localised hot spots should tell you that the cooling system is not working efficiently. Take steps to detect hot spots and ensure that they are adequately addressed. When engine components do not expand evenly, it can lead to hot spots. Also, leaky hoses can lead to localised hot spots.
So if you experience car overheating, ensure that you get the cylinder head and the gasket checked 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.
For replacement auto parts, the best way to shop for them would be through a car part finder, which is free for you to use. You may find out more about this through our website, Carpart.com.au.