The body consists of three parts: cylinder head, cylinder block and crankcase. The cylinder head is made of aluminum alloy and has fins. The new four-stroke motorcycle engine adopts overhead valve, chain drive and overhead camshaft structure. The cylinder block material is made of bimetal (abrasion-resistant cast iron cylinder liner cast aluminum heat sink) for better heat dissipation. Some motorcycles use wear-resistant cast iron cylinders, such as the Yangtze River 750 and Jialing JH70. In some small mopeds, such as the Yuhe YH50Q small displacement (50 cubic centimeter) engine, the aluminum alloy cylinder is coated with 0.15 mm hard. The structure of the chrome layer. The crankcase is made of aluminum alloy die-casting from the combination of the left and right cabinets. Some motorcycles have a buffer block between the heat dissipation signs to suppress the noise generated by the vibration of the heat sink.
2. Crank connecting rod
The crankshaft of the motorcycle engine is a combination of a left half crankshaft, a right half crankshaft and a crank pin. A ball bearing is mounted on the main journal of the left and right shafts for supporting the crankshaft on the crankcase. The two ends of the crankshaft are respectively equipped with a flywheel, a magneto, and a clutch driving gear. The connecting rod has a monolithic structure, and the large end is annular, and a needle bearing and a crank pin are combined to form a crank connecting rod set. In the two-stroke engine, when installing the piston ring, pay attention to align the opening of the piston ring with the positioning pin in the piston ring groove to prevent the piston ring from rotating in the ring groove, causing air leakage and scratching the inlet and the row on the cylinder liner. Air port.
The carburetor is an important component of the motorcycle fuel supply system and is located between the air filter and the engine intake. Generally, the motorcycle engine adopts a flat suction type for the intake air flow direction, and the throttle valve is a plunger type and a float chamber type carburetor. The carburetor structure is mainly composed of two parts: a float chamber and a mixing chamber. The float chamber is located below the carburetor, and the oil pipe is passed through the throttle switch to the fuel tank. The needle valve on the float is used to maintain a certain height of the oil level in the float chamber, so that the oil supply pressure is stabilized.