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Cylinder head is the mounting base of the valve mechanism and the sealing cover of the cylinder. It is an integral part of engine combustion chamber, which is equipped with fuel injectors, air starting valves, safety valves and indicator valves. Cylinder head of a cylindrical piston engine is also equipped with intake valves and exhaust valves. There are various air passages and water passages inside the cylinder head. Structure of cylinder head is diverse and complex. It has many holes and uneven wall thickness.

Cylinder heads are generally made of high-quality gray cast iron or alloy cast iron, and gasoline engines for cars mostly use aluminum alloy cylinder heads.

It is machined with intake and exhaust valve seat holes, valve guide holes, spark plug mounting holes (gasoline engines) or injector mounting holes (diesel engines). Also cast in the cylinder head are a water jacket, intake and exhaust passages, and a combustion chamber or part of the combustion chamber. If the camshaft is installed on the cylinder, the cylinder head is also machined with cam bearing holes or cam bearing seats and their lubricating oil passages. The cylinder head of a water-cooled engine has three structural forms: integral, segmented and single. In a multi-cylinder engine, if all cylinders share one cylinder head, the cylinder head is called an integral cylinder head; if there is one head for every two cylinders or one head for three cylinders, the cylinder head is a segmented cylinder head; if there is one head for every three cylinders, the cylinder head is called single cylinder head. Air-cooled engines use single cylinder head.

Cylinder head bears gas forces and mechanical loads caused by tightening the cylinder head bolts, as well as high thermal loads when contacting with high-temperature gases. Bottom surface (fire contact surface) is directly in contact with gas, withstands high periodic changes in mechanical load and thermal load, resulting in large mechanical stress and thermal stress. It also withstands the erosion and corrosion of gas. Cooling surface withstands mechanical tensile stress and cooling medium corrosion. Cylinder head bolt pre-tightening force causes the cylinder head to be subjected to compressive stress, and stress concentration will occur at its cross-sectional changes.

 In order to ensure good sealing of the cylinder, the cylinder head must neither be damaged nor deformed. For this purpose the cylinder head should have sufficient strength and rigidity. In order to make the temperature distribution of the cylinder head as uniform as possible and avoid thermal cracks between the intake and exhaust valve seats, the cylinder head should have good cooling performance.