The two-stroke motorcycle engine crankshaft bearing and bearing housing are interference fit, which is often said to be tight fit. This is different from a four-stroke engine. During the process of replacing the crankshaft of the engine, due to the irregular operation, the iron shovel is used to harden the hard cymbal. After the crankcase is disassembled several times, the bearing hole is enlarged to cause the bearing to loosen, and the outer circle of the bearing rotates with the crankshaft, that is, “running” The outer circle is faulty.
The crankshaft bearing "running outside circle" will affect the accuracy of the crankshaft and the power of the engine. In severe cases, the crankshaft will generate large noise, the ignition time will change, the motorcycle will be weak, and the fuel consumption will be quite high. The scooter can reach about 6L per 100 kilometers. The piston ring is excessively worn (biased). Therefore, the crankshaft bearing "running the outer circle" is not a small matter and should be taken seriously.
Usually in the case of bearing "running outside" fault, most of them are repaired by punching (using a pair of dice around the bearing seat); others are used in the crankcase housing, some small pits In order to increase the friction, the crankshaft bearings do not "run outside." There is also a method of repairing by electric welding: on the outer circumference of the crankshaft bearing, several small points are welded by electric welding to make the outer circumference of the bearing larger. It is also used: the soldering iron is soldered to the outer circumference of the bearing to repair the outer diameter of the bearing. Also used: repair the copper pad around the crankcase bearing hole. These methods can be justified as emergency treatment, but as a regular repair of the engine, the problem is much more. The main drawbacks are: it reduces the assembly accuracy of the engine crankshaft, so that the coaxiality of the crankshaft exceeds the regulations; the crankshaft has large rotational resistance, the engine is running weak, and the cylinder is severely overheated; the life of the cylinder block and the piston ring is shortened.
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