Head gasket - Information

Basic information

A cylinder head gasket is mounted between the engine block and cylinder head with the purpose of sealing cylinder pressure during combustion but also engine oil and coolant.

A perfect head gasket seal contains:

• Correct cylinder head gasket
• Straight and clean cylinder head surface
• Straight and clean engine block surface
• Correct cylinder head bolts torqued according to instructions

Different types / Materials

OEM head gasket

An original cylinder head gasket is made of softer composite material that is lined with thin metal around the combustion chambers to withstand the pressure.

MLS head gasket

MLS = Multi Layer Steel

Several thin sheet gaskets that together form a sealing joint. Usually 3-5 layers are used, but aso fewer and more layers are available. These gaskets withstand higher combustion pressures than an original composite gasket.

Cutter ring / Cooperring

This gasket is like an original composite gasket with the difference that Pyramid rings / cutting rings are located around the combustion chambers. This way, the gasket can handle extreme combustion pressures and very high engine power output..

Copper / Aluminium gasket

These exist but MLS in steel is a more common solution that works well.

Gasket thickness

OEM thickness

If the cylinder head gasket needs replacement, it's important to flatten the cylinder head to get a straight surface. The engine block should also be levelled off to maintain the original conditions. Using a thicker cylinder head gasket is necessary to keep the same compression ratio and the distance between valves and pistons as intended by the manufacturer. The thickness of the new gasket should correspond to what was removed from the cylinder head and engine block, plus the original gasket thickness.

Using the original gasket thickness on machined surfaces will increase the compression ratio and bring the valves closer to the pistons, which is less secure than the original. However, a thicker head gasket can lower the compression on an N/A engine before turbo conversion instead of changing pistons.

Compression should be changed through piston design, not a thicker gasket. Although a thicker gasket in turbo conversion can be a simple solution to boost power, the increase may not be noticeable.

Compressed vs Uncompressed Thickness

The thickness of the head gasket is measured when compressed, which is the critical measurement. Once the gasket is placed and tightened correctly, it will have the specified thickness. It should be noted that the gasket has a different thickness when not compressed, with cardboard gaskets showing more variation than steel gaskets. The manufacturer determines how much the gasket is compressed, so it is crucial to use the correct torque when tightening it.

Gasket bore

The bore size of a cylinder head gasket must not match the cylinder bore. Just as an 85mm piston is not 85mm, an 85mm head gasket is not 85mm.

Example for 85mm bore size:

A piston is smaller than 85mm - the manufacturer determines the clearance.
A head gasket is larger than 85mm, and the manufacturer determines clearance.

The gasket cannot interfere with the consumption chamber, as damage can occur. Even if you use the correct drill size, you must always check that the gasket is outside the cylinder bore. Some even use the next oversize on the head gasket to be safe. Bigger gasket bore results in a reduction in compression.

If the head gasket were to stick into the combustion chamber, engine damage would occur fairly immediately at start-up, so be careful when installing your head gasket.

Compression change

Changing compression with head gasket can be done as follows:

• Thicker gasket = Lowered compression
• Thinner packing = High compression
• Larger diameter = Reduced compression
• Smaller diameter = High compression

Head gasket selection

Choose cylinder head gasket mainly according to the degree of tuning, but partly also what the engine will be used for.

Original / lighter tuning
For those who want to keep their engine original, it's recommended to use the original cylinder head gasket. However, if you choose to grind the cylinder head, you can compensate with a thicker gasket. This may increase engine power by, but the OEM gasket should still be able to handle the slightly higher combustion pressure.

Tuned engine
When tuning an engine, it is recommended to use a steel gasket. However, if your engine experiences high combustion pressures, a cutting ring gasket is necessary.

Assembly

Cylinder head resurface.

After removing the cylinder head from the engine block, it is necessary to sand it flat. This is because a cylinder head, particularly made of aluminium, is often warped when removed. Ensure a secure fit during assembly; it must be levelled and made straight. While this process can sometimes reduce compression, A thicker head gasket should be used to compensate for the changed compression. Compression change is better achieved by modifying the piston design.

Engine block resurface

Engine block resurfacing is not a very common procedure, but it is necessary when a flat surface is required for high combustion pressures and increased power. This procedure is also required if there is any damage or unevenness on the top deck of the engine.

Cleaning of surfaces

Whether you use a razor blade, knife, straightening iron, or a special tool, it's important to avoid damaging the surface. The crucial factor is ensuring that the surface against the cylinder head and engine block is thoroughly cleaned of any dirt or deposits.

Reuse cylinder head gasket?

It is important to avoid making this mistake. The cylinder head gasket serves to connect the cylinder head and the bottom part, which are responsible for maintaining combustion pressure, oil pressure, radiator water, and crankcase ventilation, both when the engine is cold and hot. Therefore, it is crucial to ensure that a new cylinder head gasket is used when fitting an engine.

Reuse cutter rings?
You can reuse cutting rings. They are pieces of metal that can be used repeatedly if not damaged or deformed. However, it can be difficult to control this completely. Especially if you haven't taken reference measurements of the rings before. A compressed/damaged cutting ring in combination with a slightly deeper seat in the top/block is not a good combination.

Accessories

Head stud bolts

When it comes to car maintenance, it's important to use the right parts. Original cylinder head bolts are best for original cars, while reinforced bolts are often used in aftermarket repairs. These reinforced bolts provide added strength to keep the cylinder head securely attached to the lower part of the engine.

Torque wrench

In order to properly tighten the cylinder head gasket, cylinder head bolts should be used. To ensure proper fitting, a torque wrench and the original diagram should also be used to follow the correct procedure.

Problems

Head gasket movement

If you're dealing with an OEM gasket made of organic/composite material, you may find that it's softer and can shift if the engine's combustion pressure increases during trimming. Even a small gap between the cylinders can put significant strain on the gasket. To address this issue, consider using a reinforced cylinder head gasket instead of a steel gasket or one with cutting rings.

Hight coolant system pressure

If your car's cylinder head gasket starts leaking, you may notice increased pressure in the cooling system. This can cause the car to overheat and coolant to be released from the radiator cap. To check for exhaust gases, simply take a sample from the radiator header tank.

After installation problems

Even after installing a new gasket, there is still leakage. Here are some possible reasons why a new gasket may fail to prevent leakage.

• Surfaces are not clean
• The head gasket is damaged
• The gasket is installed incorrectly
  Carefully check any special head gasket installation procedures provided by the manufacturer.
• Cylinder head bolts are incorrectly tightened
• The cylinder head bolts are not tightened
• Cylinder head cracks (or block)