What cylinder-head gaskets are needed for

The cylinder-head gasket performs three actions simultaneously – it seals the engine cooling system (channels), seals the engine oil system (channels), and seals the engine timing system (cylinder cavities). That is why the requirements for this part are high. It is not necessary to forget and try to somehow save on the repair of the cylinder head or cylinder block. The gasket is a detail that is used only once, and at any engine repair, its replacement with a new one is obligatory. 

What types of cylinder-head gaskets there are: 

1. Asbestos-free – these gaskets have low shrinkage and high restorability of the material.
2. Asbestos – this type of gasket is similar in characteristics to non-asbestos gaskets, with properties such as elasticity, heat resistance, and elasticity. This type of gasket is most often used as a repair kit. 
3. Metal – this type of gasket is considered the most qualitative and effective. This type of gasket provides a more uniform distribution of surface pressure at the joint throughout the cylinder-head and block plane.

Also, see the topic: https://junkcarsus.com/article/head-gasket-repair–replacement-costs-detailed-estimation

When should the cylinder-head gasket be replaced

There is no specific warranty period after which the cylinder-head gasket must be replaced. JunkCarsUs emphasizes that the service life of this product depends on the model and general condition of the car engine, the way you drive, and other factors. But there are a number of clear signs that the gasket has ceased to fully perform its functions:

• The appearance of engine oil or coolant in the connection area at the joint between the block and the head;
• The appearance of foreign light impurities in the oil, which indicates penetration of coolant into the oil system through the gasket;
• Changes in the exhaust when the engine is warmed up, indicating that the coolant has penetrated into the cylinders;
• The appearance of oil spots in the coolant reservoir.

As JunkCarsUs points out, these are the most common signs of a worn or defective cylinder-head gasket. It is also mandatory to replace the cylinder-head gasket if the cylinder head is completely or partially disassembled.

Replacing the gasket

1. disconnecting all attachments, piping, and other parts that interfere with the removal of the cylinder head
2. cleaning the head mounting bolts of oil and dirt, to ensure convenience and safety of work with a wrench
3. unscrewing fastening bolts, and you must begin from the middle, at one time turning each bolt not more than one full turn to be sure to remove the tension
4. removing the block head and removing the old gasket
5. cleaning of seats and installation of a new cylinder-head gasket, and it must sit on all the guide bushings and fit the marked alignment slots
6. mounting the head in place and tightening the bolts, which is performed only with a torque wrench and only under the scheme given by the manufacturer for your car model, because it is important that the bolts were tightened exactly with the optimal parameters for your engine tightening torque