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Cylinder block is the main body of an engine, which connects each cylinder and crankcase into one, and is the supporting frame for installing pistons, crankshaft and other parts and accessories. Modern vehicles basically use water-cooled multi-cylinder engines. For multi-cylinder engines, the arrangement of the cylinders determines the engine's external dimensions and structural characteristics. It also affects the stiffness and strength of the engine body, and is related to the overall layout of the car.

Working conditions of cylinder block are very harsh. It has to withstand the rapid pressure and temperature changes during the combustion process and the intense friction of the piston movement. Therefore, it should have the following properties.

It should have sufficient strength and rigidity and small deformation to ensure the correct position and normal operation of each moving part with small vibration and low noise.

It should have good cooling performance, and there is a cooling water jacket around the cylinder to allow the cooling water to take heat away.

It should have good wear-resistance to ensure durability. The upper part of the cylinder block is a parallel cylinder head. The cylinders are mostly equipped with cylinder liners. The lower part of the cylinder block is the crankcase, which is used to install the crankshaft. Various accessories such as starter, alternator and engine bracket can also be installed on the outside. Cylinder blocks are mostly made of cast iron or aluminum alloy. Aluminum alloy cylinder blocks are more expensive, but are light in weight and have good cooling performance, and are increasingly used. The body is the skeleton of the engine and the basis for installation of various mechanisms and systems of the engine. All the main parts and accessories of the engine are installed inside and outside it, and it bears various loads. Therefore, the engine body must have sufficient strength and rigidity. The engine body is mainly composed of cylinder block, crankcase, cylinder head, cylinder gasket and other parts.

Water-cooled engines are often cast with upper crankcase into one body. So cylinder block is also called crankcase. Cylinder block is generally made of gray cast iron. The cylindrical cavity in the upper part of the cylinder block is called the cylinder. The lower part is crankcase that supports the crankshaft, and its inner cavity is the space for the crankshaft to move. There are many reinforcing ribs, cooling water jackets and lubricating oil passages cast inside the cylinder block. Cylinder block should have sufficient strength and rigidity. Cylinder block is usually divided into the following three types according to the installation position of cylinder block and oil pan.  

General cylinder block, the characteristic is that the oil pan mounting plane and the crankshaft rotation center are at the same height. The advantages of this type of cylinder block are small height, light weight, compact structure, easy machining and to install and dismantle the crankshaft. Disadvantage is poor stiffness and strength.

Deep skirt cylinder block, is characterized by the installation plane of the oil pan being lower than the rotation center of the crankshaft. The advantage is that it has good strength and stiffness, and can withstand large mechanical loads. But its disadvantages are poor craftsmanship, heavy structure, and difficult machining.

Tunnel cylinder block (bedplate), in this type of cylinder block, main bearing hole of the crankshaft is integral and uses rolling bearing. Main bearing hole is larger, and the crankshaft is installed from the rear of the cylinder block. Its advantages are compact structure, good rigidity and strength. Its disadvantages are high machining accuracy requirements, poor craftsmanship, and difficult to install and dismantle the crankshaft.