Different engines use different cylinder head types. The kind of head depends on many factors, such as the engine configuration, required performance, and vehicle application. Cylinder heads are crucial parts of internal combustion engines. Therefore, the right type should be installed.
Here, we will look at common types of cylinder heads used in today’s automobile. We will also go deeper and talk about materials that cylinder head manufacturers use to make these parts. Lastly, we will delve into the manufacturing process of cylinder heads to see how the components are made.
Types of Cylinder Heads
The standard cylinder head is a piece of cast iron or aluminum that sits on the top side of an engine block or cylinder. It covers the cylinder or cylinders to enable the combustion of fuel/air mixture. The head also contains pathways for intake and exhaust gases plus several other mechanical engine components.
Cylinderheads vary in design, shape, and configuration. The differences mostly depend on the type of engine which, which in turn, dictates the position of different cylinder head components. There are three basic types of these heads.
1. Flathead Cylinder Head Type
The flathead cylinder head is the earliest type. It used a simple design that comprised a single piece of cast metal with no mechanical parts. In addition to being easy and less costly to make, the head allowed coolant to flow effectively. It was also lightweight, plus it allowed for a compact engine.
Despite the simple design, the flathead engine cylinder head type had its downsides. The valves were located in the engine block and on the sides. This caused intake gases to follow a long and awkward 90° pathway, leading to inefficient combustion and low compression ratio. The design also allowed exhaust gases to remain in the ports for far too long, resulting in a cooling problem.
Due to its design inadequacies, the flathead cylinder is no longer common. Nowadays, you can only find it in small engines such as those used in lawnmowers, small tractors, and several other farm vehicles. In the car and truck category, the cylinder head remains a discontinued engine part.
2. Overhead Valve (OHV) Cylinder Head Type
This type of cylinder head has been popular for decades. It is also called the I type cylinder head and features complex construction. Unlike the flatbed type, the OHV head houses the valve train components within itself. It also contains the spark plugs and the passageways for intake and exhaust gases.
Because of the location of valves and intake passages, engines that use the OHV cylinder head type produces better performance. The flow of intake gases is faster and smoother due to the improved design of the paths. The exhaust ports are also more efficient, plus the head does not heat up quickly like the flathead type did.
The design of OHV cylinder heads also brings the camshaft nearer the crankshaft. The arrangement simplifies the drive system, enhancing the timing system. Overall, it means improved engine performance.
3. Overhead Camshaft (OHC) Cylinder Head Type
Usually abbreviated OHC, the overhead cylinder head is called so because of its design. In addition to accommodating the valve train parts, spark plugs, and intake and exhaust ports, the head also contains the camshaft.
The position of the camshaft in the cylinder head varies. It can be in the middle, between the row of valves or on top of the valves. An OHC cylinder head can be a single or dual configuration. In the single OHC type, a single camshaft operates the intake and exhaust valves.
In a dual OHC cylinder head, there are two separate camshafts for the two valves. Single or SOHC are less costly to manufacture than double or DOHC heads. However, the DOHC head types offer better performance. Cylinder head manufacturers may prefer such heads in situations where performance is a necessity.
Cylinder Head Types According to Materials
A cylinder head endures the forces of expanding gases and should be made from sturdy materials. The heat produced in the combustion chamber is also high, and the head needs to withstand temperature extremes. For reliability and durability, the requirements for cylinder head material properties include:
- Excellent casting properties (with ability to resist hot cracks)
- High creep resistance under extreme temperatures
- High tensile strength
- High ductility
- High thermal conductivity
- Low porosity
Two main metals are used to make cylinder heads: iron and aluminum. Because cylinder head material properties vary, different situations call for either iron or aluminum to be used. Here is a look at the advantage of each material.
Iron Cylinder Head- iron produces sturdy cylinder heads that resist damage well. As a result, the heads are more durable. Iron is also cheaper when compared to aluminum. The drawbacks of iron is that it makes heavy heads which may increase a car’s overall weight and lower the fuel economy. When it comes to heat-dissipation, iron performs poorly. Iron cylinder heads are, therefore, usually water-cooled.
Aluminum Cylinder Head- aluminum cylinder heads are not as strong as those made of iron. That makes them easily damaged and not as durable. They are also more costly. But the advantages of aluminum mostly outweigh the downsides, which explains its popularity with cylinder head manufacturers. Aluminum is lightweight and offers better fuel economy. The material conducts away heat three times faster than iron. That is why most air-cooled cylinder heads are aluminum.
Cylinder Head Manufacturing
The manufacturing process of cylinder heads can involve any of these methods.
- Lost-foam method
- Pressure die-casting
- Permanent mold casting
Many manufacturers cast cylinder heads using the lost-foam method. It is a simple process that also fits complex processes. In the lost-foam casting method, layers of polystyrene are used to create the cylinder head pattern. These are then glued together, and the structure coated in ceramic then dried. After drying, the cluster is placed in a flask. Sand is then poured to take up the spaces left by the foam.
After compacting the sand, molten cylinder head material is poured into the mold. The melt burns out and evaporates the polystyrene. The cast is then washed to remove sand and machined. The lost-foam method produces accurate castings. Because it involves fewer steps, it is also less costly. Cylinder heads made using the lost-foam have an excellent finish, among other advantages.
Cylinder head manufacturers produce different types of cylinder heads. Usually, a vehicle’s engine configuration determines the cylinder head type required. Each kind has its advantages and disadvantages. Cylinder head materials also vary. Again, every material has its up and downsides. This article sheds light on the different engine cylinder types and the materials used to make them. It should help you to identify and what performance benefits they hold. Also, the different materials and what they mean in terms of advantages.