A Chunlan 125T scooter (as shown in Figure 1) traveled more than 53,000 kilometers. The user reported that the power of the engine dropped sharply after thermal engine. The maintenance workers made a preliminary judgment that the engine did indeed have overheating phenomenon.

Because the car can not ride for a long time, the user asked the disassembly inspection, maintenance personnel decomposition the engine, the cylinder piston, piston ring and other friction parts are all replaced, after re-loading, start the motorcycle, less than 5 kilometers on the road, they feel the engine power drop, and hear abnormal sound.

After parking and resting for half an hour, there was no problem with the start and then riding on the road. The failure occurred repeatedly. The maintenance personnel had no other way but to ask for help from the headquarters of the company and dispatched myself to Yuhuan in Zhejiang to find the root cause of the failure. Arrived at yuhuan already more than seven o 'clock in the evening, see it is late, the maintenance station suggested to check carefully the next day.

The next morning, after breakfast came to the repair site, check the status quo of the broken down car. The car has been cycling more than 40,000 kilometers, improper maintenance of the vehicle, the engine around the dust and impurities, maintenance workers clean up the periphery of the vehicle, start the motorcycle, wait for a moment, slowly increase the throttle, the engine sound from the beginning of the low, to the medium speed sound gradually become bigger, the body began to heat, stop check.

There are many reasons for engine overheating failure. In line with the principle of first easy and then difficult, remove the spark plug. Most of the electrode color is brownish red, and the side electrode is slightly white.

Check the oil level of the carburetor float chamber, loosen the oil discharge screw of the float chamber, and make the oil discharge rubber hose port move up and down between the carburetor float chamber and the body. When it moves to the point where the float chamber and the carburetor body face down 2mm, the gasoline in the carburetor just emerges from the rubber pipe, indicating that the oil level of the carburetor float chamber is normal.

At the same time, it is also verified that most of the spark plug electrode color is brownish red, indicating that the combustion of the combustible mixture is basically normal, and the cause of overheating failure is not here.

Disassemble all the plastic parts on both sides of the vehicle, dip appropriate amount into the inlet pipe and the joint part with the cylinder head, and start the engine. No air leakage is found. Open the cylinder head cover shell, in the case of no oil door, start the engine, under the idle speed President carefully observe the cylinder head, valve rocker arm and camshaft at the lubricating oil splash, preliminary judgment of oil quantity is less.

Stop the machine, check the oil scale of the crankcase, the oil level is basically normal. According to the splash of lubricating oil at the valve rocker arm and camshaft, the feeling is not normal.

According to the analysis of mechanical principle, motorcycle driving more than 50 thousand kilometers, the source of oil flow becomes smaller, most likely with the abnormal wear and tear of the oil pump.

Decomposition of crankcase, remove the oil pump check, in addition to the oil pump internal and external rotor exist serious wear and tear, accident found crankcase contact with oil pump pump underside uneven (pictured above), oil pump installation plane itself is also uneven phenomenon (as shown in the figure below), it should be caused by the original mechanical parts processing defects.

Due to the existence of oil leakage here, resulting in a decline in oil flow, can not meet the normal lubrication and cooling requirements of the engine.

Solicit user opinions, replace the new crankcase and oil pump assembly, add high-quality selection of motorcycle special oil. Start the engine and warm up the car slightly. After a test run of more than 10 kilometers, the motorcycle accelerates normally. It is confirmed that the overheating fault of the original car is completely eliminated.