Automotive head gasket

What is a Head Gasket?

When talking about engines and cars in general, have you ever come across a car part called a head gasket? Besides having a name that suggests importance, it is also a part of many discussions regarding engine operation. You have probably heard about some of the various engine related issues a faulty head gasket can cause. If this made you think about this car part and what it does, then you are in the right place. In this article, we will explain the anatomy of the head gasket, how it works and what it does.

What is a head gasket?

The engine in your, or in any other car for that matter, has several similar main components. At the lower side, there is an engine block housing the pistons, connecting rods, and the crankshaft. On top of the engine block lies the cylinder head containing the valvetrain and camshafts. Matted together, the cylinder head seals off all cylinders and creates a closed space in which the combustion happens. The explosion then makes the pistons and the crankshaft move, ultimately creating the rotation power that drives your car.

Auto mechanic installing a new head gasket

Despite precise machining and tight tolerances that go into these parts, they still cannot keep exploding combustion gases inside cylinders. This is where the head gasket comes into play, as it comes between the engine block and the cylinder head. Being soft enough to compensate for rough surfaces between these two parts, it can create a durable seal that is completely airtight. Besides, it also ensures a sealed path for oil and coolant flowing among the various engine components. Having such a significant role for engine operation, it’s essential that the head gasket remains free of any leaks or cracks at any time.

Why are head gaskets so important?

During its entire lifespan, the head gasket has to cope with various challenges and demands that can sometimes be conflicting. Don’t forget that with each second, every cylinder in your engine fires up several times. Conditions inside the running engine are harsh, with extreme pressures, high temperatures and dynamic loads being just some of them. To make things worse, engines are not always running at a constant temperature, which creates additional problems. After starting up your car in the morning, various parts warm up at different speeds until the engine reaches its optimal running temperatures. During this period, the expansion is not the same for all materials and it can cause distortions and additional stress to the various components.

Auto mechanic holding a used head gasket

To meet all these requirements, head gaskets combine elaborate and precise design and use of top-notch materials. All head gaskets must be sturdy and durable enough to keep up with pressures and temperatures that happen inside the engine. On the other hand, they also have to be soft enough to compensate for the gap between the head and the engine block. On top of that, different expansion rates during warm-up require the head gasket to have a certain flexibility. They also have to form a dependable seal between all components and prevent coolant, oil and combustion gases from mixing at any time.

What kinds of head gaskets are there?

As there are so many engine types, it is no surprise that there are several head gasket variants. For a start, materials used for building both engine block and cylinder head play a significant role here. Next, roughness is another key factor, as smoother surfaces allow the usage of hard and sturdy head gasket materials. In the end, higher pressure and peak loads that happen in high-output engines require head gaskets that are durable and stiff.

Automotive composite head gasket

Composite gaskets

The most common type is composite head gaskets, which come in two variants depending on the materials used. It can either be a graphite gasket with a steel core or one that uses graphite, steel and special sealing components. Thanks to their flexible structure, they work well on rough surface finishes. Besides flexibility, they also come at a lower price. This makes them suitable for older engines and less demanding applications. However, these head gaskets don’t work well with smooth surfaces, as they cannot bite into the material. As there is no sufficient and reliable bond in this situation, composite head gaskets can quickly start to leak.

Metal gaskets

Other types of head gaskets you can find on the market are ones made from solid metals. Copper head gasket can withstand a wide range of surface finishes. This is because copper is malleable and will adapt to the mill marks on the block and the head. You can find these head gaskets in several forms, ranging from solid sheet, embossed solid copper to integrated tighten gaskets that include seals. Besides them, there are also embossed steel head gaskets. These gaskets were popular in the 50s and 60s and still have a limited use among tuned engines. Unlike copper ones, embossed steel head gaskets are not that flexible and require a smooth surface finish.

MLS gaskets

At the end of the line, there are also multi-layer-steel or MLS head gaskets, which are the hardest of all types and in most cases have three to five layers of coated steel. They also include embossment that adds spring, helping maintain the seal for a long period. As a result, these gaskets require the smoothest surface finish to work properly because the metal core of the gasket body will not deform at all. If there is any surface roughness, it would scrub off the coating that forms the coolant seals. You will find these in many modern cars and in highly modified engines.

Conclusion

As we’ve covered in this article, the head gaskets is a thin sheet of material that comes between the engine block and cylinder head. It is soft enough to compensate for rough surfaces between these two parts and create a durable seal that is completely airtight. In addition, head gaskets have holes that ensure pathways for oil and coolant that flow among various engine parts. Being such an important component, any failure will cause engine running issues, such as a loss of power or overheating.

 

About Bojan P

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My name is Bojan - I am a car enthusiast, specialised in the vehicle diagnosis, repair and maintenance with 10 years of practical, hands-on experience. In addition, I have a Masters degree in mechanical engineering.

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