Cylinder Head IQ Boost: Everything You Need to Know 

A cylinder head is a cast iron or aluminum structure that sits on the top of the engine block. A cylinder head is a major part of a combustion engine. This part of a combustion engine is responsible for housing the engine components necessary for the intake, ignition, and exhaust of the combustion process.

There are more moving parts in a cylinder head than any other section in a combustion engine. It may seem complicated to understand at first, but after reading this article you will have a basic understanding of what a cylinder head is.

What you will learn about:

The function of a cylinder head

The function of a cylinder head is to facilitate the intake, ignition, and exhaust of the combustion process by housing the valve train, spark plugs, fuel injectors, air intake, and exhaust ports. The cylinder head is designed to accomplish that all while keeping stable temperatures so things don’t go out of control. Cylinder heads are cast from materials like cast iron or aluminum alloys more often because of their great thermal conductivity and lightweight properties. Cylinder heads are cast with special holes and pathways for engine oil and coolant to flow independently from one another to keep the cylinder head temperature in an adequate range.

Valve train

A valve train is a unit of valves that sit in the cylinder head. The valve train has all the parts necessary for the timing of the intake and exhaust of the combustion process. Depending on the design the valve train consists of a few parts for proper operation. These basic parts are : 

• Camshafts

These are metal rods with egg-shaped lobes designed to push the valves open and leave space for the springs to close the valves shut for the process of intake and exhaust. 

• Valves

The Valves consist of a valve stem and valve face. The valves are essentially the doors that open and close, letting the air or an air-fuel mixture in and exhaust gases out after combustion. 

• Tappet/Lifters 

Tappets or lifters are the cap pieces at the end of the valve stems that receive contact with the cam lobes from the camshaft essentially transferring the pressure needed to open the intake and exhaust valves. 

• Valve springs 

Valves springs sit midway of the valve stems exerting forces the opposite way of the cam lobe force. Valve springs are the closing force to the cam lobes’ opening force. Valve springs keep the valves shut at the right times preventing float, which is when the valves remain open. 

• Rocker arms (depending on the design)

Rocker arms are found in overhead valve engine designs where the camshaft sits lower than the valve. That being said rocker arms essentially transfer the motion from the camshafts below onto the valves, opening them for intake and exhaust.

• Push rods (depending on the design)

Push rods are the slender rod-like connections between the cam lobes and the rocker arms. Push rods transfer the motion from the cam lobs to the rocker arms which ultimately opens the intake and exhaust valves.  

• Timing mechanism 

This part is made up of timing belts, chains, or gears which ultimately connect the camshaft and crankshaft. They are called timing mechanisms because they keep the camshaft and crankshaft in sync with each other so that the intake combustion and exhaust happen at the right time.

Types of cylinder head 

The valve train is an important piece of the cylinder head. The valve train design makes the differences between types of cylinder heads. Here are four types of cylinder heads: 

Side-valve (Flathead) Cylinder Head

Side-valve engines are where the valves are mounted in the engine block itself beside their correlating cylinders. This engine design allows for a more flat cylinder head design hence the name flathead.  

Over Head Valve (OHV) Cylinder Head

Often referred to as a push rod engine, these types of cylinder heads allow for a more compact engine design. With the camshaft mounted lower than the valves this cylinder head uses push rods to directly influence the opening and closing of the valves. The valves are positioned over the camshaft hence the name over head valve. 

Over Head Cam (OHC) Cylinder Head

In an OHC design, the camshaft is mounted within the cylinder head above the valves. It is driven by the timing belt or chain connected to gears that connect to the crankshaft. There are Dual Over Head Cam (DOHC) and Single Over Head Cam (SOHC) which describe how many cams are in an OHC engine. In a DOHC there are two camshafts, where one opens the intake valves and the other opens the exhaust valves. In DOHC there are four valves per cylinder.

Two valves for intake and two for exhaust. having two camshafts, where the valves are split evenly between the two allows the engine to intake more air and rev higher, making more power. However, more power means more gas being used.  In an SOHC there is one camshaft actuating both intake and exhaust valves. SOHC engines are generally more fuel-efficient than DOHC.  

Inlet Over Exhaust (IOE) Cylinder Head

The Inlet Over Exhaust design is as it sounds. This is where the intake valves are mounted in the cylinder head above the exhaust valves which is mounted in the engine block itself. 

How many cylinder heads are in an engine? 

The cylinder head count depends on what type of engine layout is present. This answer will be different whether it is a “V” or inline engine. Cylinder heads are placed on top of an engine block. More accurately it’s placed on the engine block deck. That said the more decks an engine has the more cylinder heads required. An engine block deck is the top of the engine block which clearly shows the holes cast for the cylinder. In inline engine blocks, you will only find one engine block deck. However, in an “V” style engine block where the the cylinders are split into two banks, it will show two engine block decks where the cylinders are placed. That being said Since inline engines have one engine block deck they only require one cylinder head. In a “V” style engine where there are two decks, there are 2 cylinder heads required. 

Conclusion 

As you can see cylinder heads play a crucial role in the engine’s breathing process. For the engine the more cool air that can be sucked in the more power it can make. That being said the design of your cylinder head can be a telltale sign of if your engine is on the sporty side or fuel-efficient side of things. 

FAQs

What is a normal cylinder head temp?

A normal cylinder head temperature is anywhere from 360 – 435 degrees F at high-power cruising.

What causes high cylinder head temperature?

Cylinder head temperatures can be high due to excessive engine stress. Common mistakes leading to high cylinder head temperature are using lower fuel and oil grades than recommended. High oil pressures are also an indication of high cylinder head temperatures. A bad head gasket can also cause cylinder head temperatures to be high causing loss of coolant. 

What happens when a cylinder head goes bad?

If a cylinder head goes bad the engine breaks down. This cylinder head helps the engine breathe, so if a cylinder head fails the engine will fail next.

How much is a cylinder head replacement?

With labor costing about $100 an hour, a replacement can run you about $2,000 – $3000 Depending on parts, the engine make, and the model.