Once repair a pedal motorcycle, the owner because of high fuel consumption and push to repair.
After understanding, this car for some years, has been driving more than 56000 kilometers, because of a maximum speed decline, the owner in the repair shop to replace the transmission components, small apprentice inadvertent operation, the crankshaft assembly left end of the M10 thread hair, resulting in irreparable.
After replacing the crankshaft assembly, the owner felt that the fuel consumption of the car gradually increased in less than 1 month, and the maximum speed could not reach the original 50 km/h. The maintenance workers checked the electric, oil and gas roads respectively, and no abnormalities were found, and the cause of the failure was unknown.
Roughly understand the situation, pick up the car to see the fault: start the engine, warm the car for more than 10 minutes on the road, the highest speed is only about 40 kilometers. Stop the car and open the fuel tank cap to check that there is no blockage in the air vent.
Back to the shop, remove the cylinder block and piston, check the elasticity of the piston ring, basically normal. Cylinder cylinder and piston skirt no abnormal wear phenomenon.
Disassemble the left side cover, disassemble the transmission mechanism such as transmission, clutch and triangular toothed belt. It is found that the triangular toothed belt has abnormal wear phenomenon. The width of the belt has been worn thin from the original 15.5mm to 13mm.
Ask the owner, from the last maintenance and replacement of the crankshaft so far, only to drive less than 1000 kilometers, transmission, clutch and toothed belt is replaced with the original parts, there is no fake and shoddy products, should not be in such a short period of time serious wear. Because the specific cause of abnormal wear could not be found, the tooth belt had to be replaced first.
In the assembly process, it is found that there is an obvious gap between the 15° chamfering surface on both sides of the gear belt and the transmission bevel plane. Carefully check the straightness of the gear belt at the transmission end and the clutch end, and the result is not in a straight line. The gear belt is obviously skewed to the left at the crankshaft end. The normal state should look like this.
Inquiring the owner learned that the transmission mechanism of the original machine has been used normally, no abnormal situation was found, only happened after the replacement of the crankshaft assembly.
The engine was disassembled, the crankshaft assembly was removed, and the distance from the end face of the transmission clamp of the faulty engine crankshaft to the plane end of the crankshaft arm was 48.5mm by using the depth vernier caliper, while the corresponding size of the normal crankshaft was only 46mm.
In this way, the left end face of the fault crankshaft is offset to the left by 2.5mm, so that the running center of the gear belt deviates from the center line of the transmission and clutch, resulting in abnormal wear of the gear belt slope.
When the wear exceeds the use limit, the speed ratio of the transmission mechanism has changed, so that the fuel consumption gradually becomes larger, the maximum speed can not go up.
Replace the genuine crankshaft assembly as shown in the figure above and the triangular toothed belt, and check that the straightness of the toothed belt at the transmission end and clutch end is basically normal.
After reloading the engine and starting the vehicle on the road, it felt good acceleration, and the maximum speed was up to about 50 kilometers. The three owners were tracked for about 2000 kilometers. The motorcycle was used normally, and the fuel consumption also returned to the original normal state, confirming that the big fault of the fuel consumption of the original car was completely eliminated.
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