What is a Cylinder Head? – Diagram, Parts, And Symptoms

The cylinder head is the one unmovable part across every type of internal combustion engine. It is positioned at the top of the engine, where it remains attached to the engine block by important or captive bolts, which provide proper alignment and sealing. This is the most highly loaded element in the engine.

The necessary functions of this piece are those of sealing the upper portion of the cylinders with the associated parts, which are subjected to high stress during engine operation. Engine operating defects that arise due to faults in the cylinder head are invariably disastrous to other parts of the engine.

What is a Cylinder Head?

A cylinder head is part of an internal combustion engine and sits on top of the cylinder block and forming the top of the combustion chamber. It’s sealed in place with the head gasket.

In a valve-in-head type engine, the head is just a plain plate. However, in later model overhead valve/overhead camshaft engines, the cylinder head is more complicated and incorporates certain motor functions like intake and exhaust openings, water channels, valves, camshafts, and even spark plugs and fuel injectors.

Most straight engines have a single-cylinder head shared by all cylinders and most V engines have a two-cylinder head (one per bank of cylinders).

In all types of Perkins engines that utilize water for cooling, the cylinder head possesses ducts and passages.

These ducts permit the circulation of coolant, made up of water and antifreeze, to remove excess heat from the main body of the engine and transfer it to the radiator to mitigate overheating and damage risks. Not surprisingly, the cylinder head is subjected to extremes of temperature, which it has to endure.

What does the cylinder head look like?

The cylinder head makes up the upper ceiling of the combustion chamber located above each of the pistons, together with the spark plug sockets and injector holders.

The head also merges the accompanying valves, guides associated with the cylinder head, and an assortment of exhaust and intake duct hoses with their respective return springs.

Frequently, the upper part offers one or two supporting locations for a camshaft, or for bucket tappets, or for a rocker arm. The cylinder head also has the ducts that are needed for the passage of fluid coolant.

The cylinder head performs additional functions: it also thermally insulates the engine, since the inside may reach temperatures of 300 degrees Celsius, but the outside needs to stay below certain values.

The average temperature needs to stay cool to the tune of twenty degrees Celsius. The upper part of the engine is the hottest at seventy percent of the heat released. The stress must account for high mechanical levels.

Aluminum heads are commonly used in some applications where greater thermal conductivity is necessary, but, in consideration of the intended purpose, a cylinder head less expensive cast iron alloy is employed.

These characteristics, together with its important role, make it one of the most complicated components of the engine, and the design, along with the manufacture of the various parts, is time-intensive and needs careful detail.

Construction

The cylinder head can be manufactured with cast iron or cast aluminum. Even though cast aluminum is harder and costlier to create, it is preferred because it saves weight and has superior heat dissipation capabilities; most gasoline engines use aluminum heads, while diesel engines still use cast iron due to its strength.

The upper half of an engine consists of oil galleries and coolant passages, which are more intricate than the lower half of the engine; the head can be contoured using the lost-foam casting technique.

Components Of a Cylinder Head

Here are some parts descriptions of cylinder heads:

• Inlet and exhaust runners: These ensure that the air-fuel mixture gets into the combustion chamber and that exhaust gases purge from the cylinders.
• Inlet and exhaust valves:  These control the flow of the air-fuel mixture with gases into and out of the head.
• Camshafts: These open and close the valves.
• Spark plugs: These ignite the fuel.

How do Cylinder Heads work?

The combustion chamber is created when the cylinder head is attached to the top of the cylinder block. The combustion chamber contains a spark plug that ignites the mixture and gas present within. The cylinder head merges with valves that open to the cylinder.

An intake valve admits a mix of air and fuel into each cylinder, after which it seals. The piston proceeds to move up rotationally and compress the fuel and air mix. After the fuel and air have been successfully compressed into a dense volume, the spark plug ignites it.

During combustion, the gas expands violently, forcing the piston down. When the piston moves downward, the exhaust valve opens, allowing the gas to exit the engine. The camshaft rotates to ensure that each mechanical action happens at the specified time and with the others.

Types of Cylinder Heads

• Flathead Cylinder Heads: These types of cylinder heads were the first ones invented. They were designed simply to protect the cylinder block, so flathead engines cannot offer aerodynamic performance. This type of cylinder head severely limits engine performance due to restricted airflow.
• Overhead Valve Cylinder Heads: These types of cylinder heads are more advanced than flathead cylinder heads. The camshafts are located overhead of the valves, so they are known as overhead valve cylinder heads. They are fitted with a complex system of pushrods and valves for proper, smooth air passage.
• Overhead Camshaft Cylinder Heads: These are the most modern designs of cylinder heads. The camshafts are located inside the cylinder head, known as the spindle, and so there is no requirement for pushrods. This aids in proper air passage and hence improves engine performance.

Why Do Cylinder Heads Fail?

The primary cause of cylinder head failure is excessive heating due to many reasons, like loss of coolant, failure of the head gasket, or narrowing of cooling spaces.

In some cases, the cylinder head may be cracked or damaged beyond repair, which effectively puts the engine out of commission until repaired! Any repairs and maintenance must be executed as early on as possible to help avoid this condition.

The cylinder head may warp due to the immense pressure and extreme change in temperature. It is no longer capable of providing a flat surface where the head gasket is to be placed, which may lead to costly repairs or complete replacement of the engine.

Certainly, heads of cylinders made of aluminum face distress of this type. Different engines have different degrees of tolerance to endure cylinder head warping. For a few, tolerating a greater amount of deformation while still functioning perfectly is possible.

If your cylinder head does warp, it may be possible to take it to a mechanic who specializes in unbolting the jagged edges – otherwise, there’s no other alternative than replacing it.

What Are the Symptoms of Cylinder Head Failure?

The drivers must recognize the symptoms at the earliest to prevent any further damage. If the cylinder head suffers failure, the engine will stop functioning along with the vehicle.

• Decrease in coolant levels or change in temperature of the coolant.
• Reduction in oil levels.
• Decline in the performance of the engine.
• There is an exhaust smoke emission.

The most familiar failure causes of a cylinder head are overheating due to the loss of coolant, the failure of the head gasket, and restricted coolant flow. In the worst-case scenario, terminal engine damage could occur due to a cracked or broken cylinder head.

What is the repair cost for a cylinder head at a garage?

In the US, the cost for purchasing a new cylinder head ranges from $3,522 to $3,871. The price of the service is estimated to cost around $1,217 to $1,535, while the required parts would total $2,305 to $2,337.

Under ideal conditions, a cylinder head can last for as long as the engine does. However, if scheduled maintenance, which includes oil changes, is neglected, the head, valves, and several other components can face severe damage. Additionally, overheating the engine most certainly damages the cylinder head.

FAQs.