A CL125-3A Chunlan Tiger motorcycle travels 50000 km as shown in the following picture. Because of the user's carelessness in using the vehicle, he forgot to add lubricating oil on time and pulled out the piston and cylinder. The maintenance man replaced the piston, piston ring and cylinder block, started the engine, and the test run was basically normal.

Three months later, the user came to the maintenance station to report that nearly 3L of lubricating oil had been added in the case of driving less than 1800 km. The repairman started the engine and found no abnormal blue smoke from the exhaust pipe. He took the user to sit in the car and told him to pay attention to whether there was any abnormal phenomenon when driving on the way. Ride about 10 kilometers, the user said that no blue smoke from the exhaust was found, and the reason for the abnormal consumption of oil was unknown.

Under normal circumstances, the oil consumption is too large and the exhaust blue smoke has a direct relationship, now the user confirmed that the vehicle on the road without blue smoke phenomenon. According to the mechanical principle analysis, in addition to the above factors, if the engine overheating phenomenon, the oil will slowly evaporate through the crankcase vent, therefore, the oil consumption is too large should also be related to the crankcase vent oil evaporation.

To this end, maintenance personnel found a piece of plastic foam, tied with fine hemp rope, and then try to hang in about 5 ~ 10mm from the crankcase ventilation hose mouth, pay attention to not clog the ventilation pipe mouth, to ensure that the air flow is smooth.

After 20 kilometers of continuous driving, no obvious oil stains were found on the plastic foam. The hypothesis of crankcase oil evaporation does not exist. So what is the cause of abnormal oil consumption?

In desperation, the maintenance personnel had to decompose the engine, remove the cylinder, piston and ring for detailed inspection. The piston ring is placed on the top of the cylinder (that is, the piston is above the first piston ring at the top dead center), and the piston ring opening clearance is checked with the gauge piece, the first is 0.25mm, the second is 0.45mm, at the lower limit of the standard opening clearance of the piston ring, and the piston ring is checked in the cylinder without light leakage phenomenon.

The opening gap is not big, and there is no light leakage around the ring. Then, and checked the cylinder head on the valve pipe oil seal, there is no abnormal wear phenomenon, which is a bit strange.

Carefully analyze the causes of abnormal oil consumption, according to the principle of internal combustion engine analysis, piston ring with the piston for up and down movement process, in addition to the suction travel ring and ring groove on the plane of contact, the other three travel and ring groove contact the lower side.

If the flatness of the lower side of the piston ring or the flatness of the lower side of the ring groove is out of line, the gas in the combustion chamber will leak out through the lower plane channel where the piston ring and the piston ring groove often contact.

The relevant information shows that if the contact area between the lower end face of the ring and the ring groove is reduced from 100% to 90%, the leakage of the piston ring will increase by about 5 times, causing leakage and oil channeling fault, and because the oil is slowly leaking out, it will not produce the phenomenon of blue smoke from the exhaust pipe.

This fault point is relatively hidden, if not careful attention, general maintenance personnel is not easy to detect.

The piston ring of the fault machine was taken to the table lamp under careful care, and it was found that the lower side of the first and second piston rings were obviously distorted and uneven, as shown in Figure 2.

Replace the new piston ring sent directly by the manufacturer, start the engine, warm the car for a while, the road test more than 10 kilometers, basically normal. It is given to the user to continuously track the vehicle driving more than 2000 kilometers. The user adds 500ml lubricating oil, and the fault of excessive oil consumption of the original machine is completely eliminated.