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Do you know what a piston does?

Fundamentals of pistons

First of all, the pistons of gasoline and diesel engines are different in material and shape design (the most obvious is the shape of the top of the piston)

The most common is the cast iron piston and steel piston commonly used in some old models, the manufacturing process is not high, and the cost is low.

Now a large number of new cars use alloy pistons, mainly in order to reduce the weight of the single-piston assembly, make the engine better performance of energy saving, and improve the engine’s dynamic response.

There is also a combination of pistons (the whole piston assembly can be divided into three parts: piston top, the piston head, and piston skirts. Some cutting-edge engines can make these three parts with different materials or processes to obtain better engine performance. F1 engines often use a combination piston design)

Finally, the machining mode of the piston itself can also be divided into forging and casting types. But to make it clear that the piston is just one of the many parts of the engine, and it can’t simply judge the performance of the entire engine according to the material or process of the piston or other parts (such as the cylinder head or cylinder block).



The combustion chamber is formed under the cylinder head and above the piston.

Bear the pressure of burning gas in the cylinder.

Transfer this force through the piston pin to the connecting rod, and drive the crankshaft rotation.

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Do you know what a piston does?

Working conditions

High temperature

High pressure,

High speed

Difficulty in heat dissipation and poor lubrication.

Requirements for piston

Having enough stiffness and strength, the transmission of force is reliable.

Good thermal conductivity, small thermal expansion coefficient, and good wear resistance, high-temperature resistance, and high-pressure resistance.

The quality should be as small as possible, reducing the inertia force of reciprocating motion.

Structure of piston

It consists of a top, head, and skirt.

Piston top: part of the combustion chamber.

Action: to withstand gas pressure, its shape is related to the combustion chamber.

Shape: flat top, concave top, convex top, molding top piston.

Note: the piston has a logo at the top of the installation, and should not be installed in the back and forth order. Its top is marked with a clean in, row, or arrow front installation.

Piston head

The part above the piston ring is called the piston head.


Three rings: two air rings, one oil ring.

Four rings: three to the air ring, and the oil ring.

Five rings: three air rings, two oil rings.

Heat insulation groove: some piston in the first ring groove above the position of a lighter ring circle groove, the purpose is to prevent the heat at the top of the piston to the first air ring. Reduce the heat at the top of the piston, reduce the heat load of the first ring, and increase the service life of the first ring.

Piston skirt

The part below the piston ring includes a piston pinhole.

Function: To provide a guiding role for the piston. And under lateral pressure, it also plays a role in heat dissipation.

Features: the skirt is long, to provide the piston with a good guide, at the same time to play a good heat dissipation.

Some live in the group without a gap: it is designed to prevent the piston from running to the bottom point and the crank collision.

Part of the piston skirt has a circular arc groove.

The purpose is to prevent the engine from working for a long time, the piston is affected by high temperature and the expansion is stuck in the cylinder sleeve, which is hot expansion and cold shrinkage.


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