In this article, you will learn what is cylinder head? Its parts, functions, uses, and types of cylinder head are explained in detail with diagrams. Download the PDF file at the end of the article.
What is Cylinder Head?
In an engine, the top of the cylinder is closed with a separate cast piece called the cylinder head. The cylinder head is bolted to the upper part of the cylinder block. This joint is covered by a head gasket. It consists of a combustion chamber, spark plugs, and sometimes valves (in the I and F-heads).
In most engines, the cylinder head includes passages that deliver air and fuel to the cylinders, and which allow exhaust gas to exit. The cylinder head is usually made of gray iron or aluminum alloy. Aluminum has the advantages of being lightweight and having high thermal conductivity.
Parts of Cylinder Head
Following are the parts of the cylinder head:
- Head gasket
- Intake and exhaust ports
- Head valves
- Head combustion chamber
- Spark plugs
- Fuel injectors
- Head camshaft
- Additional cylinder head parts
1. Head Gasket
These are located between the cylinder head and the engine block. A head gasket is bolted on top of the engine housing. These gaskets act as a seal between the cylinder head and the engine block. This prevents the oil and engine coolant from leaking or mixing.
2. Intake and Exhaust Ports
The intake and exhaust ports are part of the cylinder head. The intake port is meant to circulate air through a channel into the cylinder head and combustion chamber.
After the combustion process, the gases are removed from the combustion chamber by the exhaust port. This avoids the build-up of internal pressure, which can result in an explosion.
3. Head Valves
An engine has valves to close and open, the purpose of which is to stop or prevent the entry of air and fuel into the combustion chamber. In an internal combustion engine, each cylinder has two valves – the intake valve is usually larger and the exhaust valve is smaller.
4. Head Combustion Chamber
The head combustion chamber is called the core of the engine. In which the air-fuel mixture burns to generate the power to move the vehicle. Combustion chambers are available in various shapes and sizes. Well, it depends on the engine that you have and the application of the vehicle.
5. Spark Plugs
The spark plug provides power to the combustion chamber to ignite the air/fuel mixture. Plugs are mounted on the cylinder heads, their tips leading directly to the combustion chamber. They are usually threaded to ensure an airtight seal.
6. Fuel Injectors
7. Head Camshaft
The cylinder head also includes the camshaft. In this, the camshaft operates to open and close the valves. The crankshaft is one of the engine block components, uses a belt to drive the cylinder head camshaft.
8. Additional Cylinder Head Parts
The cylinder head also has ports for the purpose of lubrication to cool the engine. Cylinder head port designs vary, as the head designs do. Basically, the purpose of every type of construction is to make the part as efficient as possible.
Construction of Cylinder Head
It is cast separated from the cylinder block to eliminate it for cleaning carbon and grinding valve. To maintain compression within the cylinder, a flat piece of gasket is arranged between the cylinder head and the cylinder block.
In some cases, such as racing car engines, a separate head is not used. But a single piece of the cylinder block and the head is difficult and costlier to make, and internal parts of the engine are not as accessible.
Depending on the valve layout, the cylinder head may have camshafts, rockers, and valves. Waterways are provided to accommodate valve and plug seating. From the mechanical point of view, the design details of a detachable cylinder head are perhaps the most difficult.
The following points should be kept in mind while making detachable heads:
- The bore of the cylinder or linear should not be distorted by the pull of the holding down studs.
- The circulation of coolant in the cylinder head should be taken as far as possible to the top end.
- To ensure a sound gas tight joint, the holding own studs must be distributed as uniformly as possible around the circumference of each cylinder.
Function of Cylinder Head
The cylinder head plays an important role in a motor vehicle. The structure of the cylinder head is complex and consists of many ports. One of these ports is designed to work, and their common roles explain the value of this engine part.
It provides the mounting for various components such as inlet and outlet exhaust valves and ducts, spark plugs, fuel injectors, and camshafts. In addition, it gives way to coolant, oil, and combustion gases.
The cylinder block absorbs the heat produced by the engine and, therefore, generates cooling to prevent engine failure. It seals the combustion chamber and serves as the engine’s mechanical control powerhouse. It also takes away the compression resulting from the combustion pressure.
Four Designs of Cylinder Head
Figures show four designs of cylinder head and location of valves.
- At (a) is the popular side valve construction with all valves in line, detachable head being of turbulence type. The piston closely approaches the flat position of the cylinder head.
- At (b) is shown reverse valve construction of the cylinder head which gives good volumetric efficiency, as large diameter inlet valve may be used, and the valve port gives direct access to the bore.
- In (c) is shown cylinder head with vertical valves in single line permitting the simple push rod and rocker gear.
- At (d) is an ideal hemispherical head which is used in many high performance designs. In this design, the flame travel is short and high compression ratio can be readily provided by a domed piston crown.
Types of Cylinder Head
Following are the types of cylinder head:
- Flat head cylinder head
- Overhead valve cylinder head
- Overhead camshaft cylinder head
1. Flathead Cylinder Head
These types of cylinder head consisting of a single piece of cast iron metal without any mechanical parts. Apart from the simple design, the flathead engine cylinder head type had its drawbacks.
The valves are located on the sides of the engine block. This causes the intake gases to move at a 90° angle, leading to inefficient combustion and a low compression ratio. Due to its design flaws, the flathead cylinder is no longer seen as common.
These are easy to manufacture and require low cost, the head allows the coolant to flow effectively. It is lightweight, as well as allowing for a compact engine. It can be found in small engines such as those used in lawnmowers, small tractors, and agricultural vehicles.
2. Overhead Valve Cylinder Head (OHV)
Overhead-valve cylinder heads are complex in construction and are also known for I-type cylinder heads. This includes the valve train parts, spark plugs, and the passageways for intake and exhaust gases.
Engines with OHV cylinder head types tend to perform better due to the location of the valves and intake passages. In this, the flow of intake gases is fast and smooth due to the better design of the paths.
The advantage of installing this type is that the exhaust ports are also more efficient, plus the head does not get hot when compared to the flathead type. It also brings the camshaft closer to the crankshaft.
3. Overhead Camshaft Cylinder Head (OHC)
These types of cylinder head allow for valve train parts, spark plugs, and intake and exhaust ports, with the head, also housing the camshaft. In this, the location of the camshafts in the cylinder head varies. This can be in the middle, in the middle of a row of valves, or at the top of the valve.
An OHC cylinder head is available with two configurations which are single and dual. In a single OHC cylinder head, there are intake and exhaust valves in a single camshaft. In a dual OHC cylinder head, there are two separate camshafts for the intake and exhaust valve.
Advantages of Cylinder and Head
Following are the advantages of the aluminum alloy cylinder and head:
- Higher heat conductivity which is about three times that of cast iron.
- Light in weight.
- Increased compression ratio without detonation due to the heat conductivity.
- Better cooling while the engine is running.
- Greater power output and low fuel consumption due to increased compression ratio and better cooling effect.
- Engine warms up more quickly and requires a smaller radiator.
Following are the disadvantages of the aluminum alloy cylinder and head:
- The engine costs more due to quickly aluminum alloy.
- It is laible to be crusted out of shpe by holding down studs due to low modulus of elasticity.
- Due to higher thermal expansion, greater clearance is required between the piston and cylinder.
- Greater possibility of corrosion by cooling water.
- Sometimes, it is necessary to use cast iron valve seatings and spark plug inserts.
- Due to inter-metallic corrosion between steel studs and aluminum alloy, the head may stick to the cylinder blocks.
Applications of Cylinder Head
Following are the applications of cylinder head:
- The cylinder head is integrated with the cylinder block, in some cases commonly done in racing cars to achieve a gas-tight joint.
- The detachable head type has more benefits than integral construction.
- However, some heavy-duty engines requiring higher cooling rates such as those in racing cars may use copper alloys.
As you know now, it is a detachable metal that fits over the top of the cylinder block. Which is mainly used to close the combustion chamber of the engine from above. So now, I hope I’ve covered everything about the cylinder head parts, and their function.
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