Cylinder head bolt function is to connect - it is typical for a screw. In cars this concerns the cylinder head. Cylinder head gasket and crankcase. The purpose of this connection is to ensure, in particular, the tightness between the cylinder head and the valve cover. This prevents motor oil, combustion gases or coolant outflow. Modern cylinder heard bolts are so designed that they do not need to be tightened. This is due to two components. On the one hand this is due to the nature of modern cylinder head bolts (waisted shank screws or screwed captive bolts, very high tensile strength) and the material of the cylinder head gasket, which practically does not "settle".

Currently applied method of the bolted joint can be described as a method of the angle of rotation controlling. When designing the screw connection between the valve cover and the cylinder head, it is necessary to take into account thermal forces. This problem concerns the time-varying heating of the cylinder head bolts, cylinder head and crankcase. That is why waisted shank screws or screwed captive bolts are used. The cylinder head bolts are durable parts. Actually, they need to be replaced when it is necessary to replace the cylinder head gasket. In this case bolts need to be replaced because of their peculiarity.

When the repair concerns the cylinder head, the gaskets and the cylinder head bolts, it is recommended to do it in a repair shop. They have a certain professionalism, experience and tools. If you need any car parts, our Internet store is at your disposal. Here you will find high-quality cylinder head, cylinder head gasket, expansion tank, stub axle, brake caliper and many others.

How to detect faults of the engine Cylinder head screws

The state of the engine cylinder head bolts is very important: they should not be damaged even to the slightest extent. The fasteners can withstand the loads of up to 5,000 kilograms, when the engine runs at the maximum RPM. Make sure that the thread of the bolts is not clogged. Should even microscopic foreign objects or dirt get into the thread, the cylinder head may get destroyed.

It is not recommended to lubricate threads of the bolts with highly viscous oil. This may result in jamming of the component.

Special attention should be paid to the tightening torque of the bolts. The bolts are to be tightened with a torque wrench. The tightening torque is defined by the type of the engine, and by the material the cylinder head is made of. Its standard value is within 17–21 Nm. The value for a specific vehicle model should be specified in the technical documentation.

If any symptoms of bolts defects are detected, they are to be immediately checked. When used correctly, the components may be used during up to 200,000 kilometers of mileage.

You may notice that bolts of the cylinder head need diagnostics by the following symptoms:

• the engine operation is accompanied by extraneous noises;
• the engine vibrates at high rpm;
• the system has been depressurized.

The reasons of cylinder head bolts malfunctions

The bolts used for sealing the engine cylinder blocks of modern vehicles have special characteristics. They are made of the material that can stretch in case of repeated tightening. It is therefore not recommended to reuse them after dismantling.

It is absolutely prohibited to re-tighten bolts of the TTY type that are used in engine cylinder heads made of aluminum. They cannot ensure the required compression of the gasket, and may break.

Another reason of bolts breaking is incorrect tightening torque during installation. It is also important to use small amounts of oil during installation, since excessive amount of oil may be the reason of unreliable attachment of the components.

A frequent reason of cylinder head bolts damage is using poor quality lubricant and mechanical impacts during repair. Therefore, if you have no appropriate experience, their adjustment and, if necessary, repair, should be entrusted to specialists.

Replacing the Cylinder head screws

The bolts of the cylinder head are not subject to repair. In case of even slightest defects, they are to be replaced. It is recommended to replace all the bolts at once, to avoid uneven loading.

Never cut a new thread on the bolts. This may result in their jamming and failure of the bolt head recesses. In these circumstances, complete replacement of the cylinder head will be required.

The bolts are to be tightened in a strict sequence: from the edges of the cylinder head to its center. The bolts are to be tightened in three stages, which allows to avoid deformation of the gasket and shifting of the cylinder head, thus maintaining the tightness of the system.