What is usually marked on the top of the piston

秦浪

2022/08/22

Usually, the piston has a forward mark on it. The installation direction of the piston is strictly specified. Gasoline engine pistons have pits that avoid the valve, and diesel engine pistons have a design that avoids cooling nozzles. If the piston is installed upside down, it may cause damage to the piston or other parts (nozzle and valve).

Additionally, some engine pistons are designed with an eccentricity in the piston pin bore. If the installation defect affects the performance of the engine. Therefore, the installation direction of the piston is strictly specified. This requires markings on the top surface of the piston to distinguish the orientation. The markings are usually towards the front of the engine.

As shown in the figure below, there are three main marks on the piston: one is the numbers 1 and 2, or the letters A, B and C, which represent the outer diameter of the piston; the other is the mark for the installation direction of the piston. The piston number is also printed on the top of the piston, which must match the cylinder number, that is, the No. 2 cylinder should be equipped with a "2" piston, and the No. 1 cylinder should be equipped with a "1" piston.

The marked pistons on the pistons precisely match the cylinder walls and are assembled in groups. Therefore, pistons cannot be mixed between different cylinders in the same engine. The top of each piston is marked to avoid mixing, and there are generally corresponding markings on the body.
When installing the piston, make sure the piston is oriented correctly. Assemble the piston and connecting rod into the cylinder so that the "in" mark on the top of the piston faces the intake side, the "EX" mark faces the exhaust side, and the mark on the piston head faces the crankshaft pulley side.

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