When the engine is working, the metal wear debris generated by the friction surface of the parts, 

the dust in the atmosphere, and the carbon particles generated by the incomplete fuel combustion will penetrate into the engine oil.

 The engine oil itself will also produce colloidal deposits due to heat and oxidation. 

These impurities will be mixed in In the oil. 

If such dirty engine oil is directly sent to the surface of the moving parts, 

the mechanical impurities in the engine oil will become abrasives, which will accelerate the wear of the parts, 

and cause blockage of the oil passages and cementation of parts such as piston rings and valves. 

Therefore, an oil filter must be installed in the lubrication system so that the circulating oil can be purified before being sent to the surface of the moving parts. 

Ensure good lubrication of the friction surface and prolong its service life.