1. Lubrication: There is rapid relative sliding between the piston and the cylinder, between the main shaft and the bearing bush. To prevent the parts from wearing too quickly, an oil film needs to be established between the two sliding surfaces. The oil film of sufficient thickness separates the surfaces of the parts that are relatively sliding, so as to reduce wear.

2. Auxiliary cooling and cooling: The oil itself does not have a cooling effect due to its low specific calorific value and inside the engine. However, heat energy is generated in the engine due to the combustion of fuel. When the engine is working, the oil can bring the heat back to the oil tank and then dissipate it into the air to help the water tank to cool the engine. The real cooling effect is the water (or antifreeze liquid) outside the engine casing.

3. Cleaning and cleaning: Good engine oil can bring the carbide, sludge and wear metal particles on the engine parts back to the oil tank through circulation, and wash the dirt generated on the working surface of the parts through the flow of lubricating oil.

4. Sealed and leak-proof: The oil can form a sealing ring between the piston ring and the piston to reduce the leakage of gas and prevent the entry of external pollutants.

5. Anti-rust and anti-corrosion: The lubricating oil can be absorbed on the surface of the parts to prevent the contact of water, air, acidic substances and harmful gases with the parts.

6. Shock absorption and buffering: When the pressure of the engine cylinder port rises sharply, the load on the piston, piston chips, connecting rod and crankshaft bearing is suddenly aggravated. This load is transmitted and lubricated by the bearing, so that the impact load it bears can play a buffering role. .