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What is the structure of the four stroke Outboard Engine?
Jan 02, 2018

What is the structure of the four stroke Outboard Engine?

In the four stroke engine, the crankcase does not hold the combustible mixture, does not set the intake port, and does not install the intake mechanism. The crankcase of riding motorcycle and engine is equipped with crankshaft connecting rod assembly, timing chain and speed changing mechanism. The oil in the cavity is equipped with rotary parts such as crank shaft and other parts to splash and lubricate the friction parts. In a sitting motorcycle, the crankshaft box is only equipped with a crankshaft and connecting rod, and other parts of the transmission are installed in the other casting cavity and are not connected to the crankcase.


The crankcase of the four stroke Outboard Engine is almost connected with the cylinder part. It ensures the good sealing performance of the piston ring and the cylinder wall by using the effective bonding of the piston ring and the cylinder wall, and prevents the gas leakage in the cylinder. When the piston runs downward, the crankcase is in a positive pressure state. When the piston runs up to the top point, the crankcase is in a negative pressure state, and the air pressure in the crankcase is always between positive pressure and negative pressure. When gasoline engine works, there will be more or less a small amount of combustible mixture and exhaust gas running through the tiny gap of piston ring and cylinder wall into the crankcase, so the air pressure in crankcase is slightly higher than atmospheric pressure. When the engine is extinguished and cooled, the gas that moves into the crankcase will be condensed into water or waste oil. If it is not discharged in time, it will seriously affect the normal operation of the engine. Therefore, at the upper entrance of the crankcase of the four stroke Outboard Engine, the "ventilation pipe" connected with the atmosphere is set up to ensure the internal and external pressure balance. In order to reduce the pollution of the oil vapor in the crankcase to the air environment, the modern engine adopts closed crankcase ventilation system, and a special hose is applied to the air filter to make the unburned fuel burn again.



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