2. The precision of pistons produced by regular manufacturers is very high
There are generally grouping marks on the top of the piston, usually there are groups A, B, C and D, which are the size grouping marks on the piston skirt. In addition, there are several very fine grooves on the piston skirt, which are mainly used to store lubricating oil to enhance the lubrication function of the piston skirt. Due to the rough processing, it is impossible for defective pistons to undergo such a precise processing technology.
The wall of high-quality piston skirt is very thin, and its wall thickness is uniform. The size of one side of the piston skirt can be measured with a vernier caliper. If a digital display vernier caliper is used for measurement, the measurement result is more accurate because of its high precision. If the difference in wall thickness is more than 0.20mm, after the temperature of the piston rises, due to the different wall thickness of the skirt, the thermal deformation will be large and uneven, so that the size of the piston skirt will not reach its ideal perfect circle, which will not only easily cause leakage , and an abnormal knocking sound will be produced.
3. The cross-section of the piston skirt of the regular manufacturer is non-circular
The cylindrical part from the bottom ring groove of the piston (referring to the oil ring groove) to the bottom surface of the piston is the piston skirt, which acts as a guide and bears side pressure when the piston reciprocates in the cylinder. The piston in non-working state is different from its working state under stress and heat. This is because the piston will be deformed to varying degrees when it is heated and stressed.
When the piston is in working condition, due to the force and heat, the dimensional deformation of the piston along the direction of the piston pin increases, while the deformation along the direction perpendicular to the piston pin is small. Therefore, in order to offset and adapt to its thermal deformation, ensure that the shape of the piston is cylindrical when it is working, so as to adapt to the inner wall of the cylinder and have a suitable fit clearance. In the non-working state, the size of the head of the piston viewed from the axis smaller, while the skirt is slightly larger;
The cross section of the piston (that is, the cylindrical section) should be oval when the major axis is perpendicular to the axis of the piston pin. The difference between the length of the cross-section of the piston produced by the regular manufacturer is 0.15 ~ 0.25mm. You can use a vernier caliper or a digital caliper to measure the dimensions of the above relevant positions, and compare them to distinguish the advantages and disadvantages.
