Why do motorcycles burn engine oil?

Many riders know the word burning engine oil, but how serious is the damage to the engine caused by burning engine oil? Maybe many people don't know. In fact, burning engine oil is only a general intermediate fault for the engine, and it may cost tens of dollars to solve the problem of burning engine oil. Isn't it incredible? The situation of burning engine oil is usually directly reflected in the color of exhaust gas, so let's start with the color of exhaust gas. There are three colors of white smoke in motorcycle exhaust: healthy color generally appears in winter, engine temperature is low, and exhaust temperature is higher than ambient temperature. Of course, the high-temperature gas after combustion immediately cools down and emits white exhaust. White exhaust generally indicates that the car is in good combustion condition. With the increase of engine temperature, the temperature around the exhaust system increases and the white exhaust gradually disappears. Black smoke: indigestion color black indicates that the engine combustion system is faulty, just like the human digestive system is not good, and the fuel system needs to be adjusted. When there is black smoke in the exhaust gas rich in oil, first check whether the air filter is blocked, and then adjust the mixing ratio. Blue smoke: when the exhaust color is blue, it means that the mechanical system of the vehicle is faulty, indicating that the engine has the phenomenon of burning engine oil, commonly known as "burning engine oil"; This is also the reason why most riders feel depressed when they encounter blue smoke from exhaust. This situation needs to be dealt with in time to avoid the aggravation of the fault and cause greater losses. Three reasons for burning oil 1 and factors of piston assembly 670% of common cases of burning oil are caused by the wear of piston assembly, which is composed of piston, piston ring, piston pin and other basic components, and the wear of piston in piston assembly is the main factor of burning oil. After the piston ring is worn, it will be slightly difficult to start and the fuel consumption will increase. If the wear is aggravated, it will show the symptoms of burning oil on the exhaust. If ignored, the next step is piston wear. Because the piston ring not only plays a sealing role, but also plays a guiding role, when the piston ring is too worn, it will swing when it moves up and down, resulting in the wear of the cylinder block, so it should be treated as soon as possible to avoid causing greater losses. 2. Valve group factor Another important reason for burning engine oil is the abnormality of the valve assembly. Valve assembly is mainly composed of valve, valve guide, valve oil seal and valve spring. When the valve sealing belt is worn, it will not only cause the cylinder to sag, but also cause oil burning. But this is not the most important factor. The oil seal on the valve stem will restrict most of the oil from flowing into the combustion chamber. When this oil seal fails, a large amount of oil will flow to the valve seat through the valve stem. When the valve is lifted, the oil will flow into the combustion chamber along the exhaust valve, causing the oil to burn. 3. If the above two situations are excluded, there are still some factors that will also cause engine oil to burn. If the amount of oil added exceeds the standard amount, excess oil will enter the combustion chamber due to the large running resistance of the crankshaft when the engine is working; The piston ring is installed in the wrong direction, causing the oil to escape upward. These factors will also cause the engine oil to participate in the combustion, making the tail gas blue. In addition, if the engine's breather pipe leaks, it will cause the oil to overflow with the exhaust gas, resulting in abnormal oil consumption. These situations can be effectively avoided through adjustment and careful use. It should be explained here that engine oil is also a consumable, and about 5% consumption is normal when the engine is working, which is not within the scope of burning engine oil. Knowing these reasons, let's learn more about the mechanical composition of the above two related components, and then study the solution when oil burning occurs. Piston assembly 1 introduction. Introduction of piston rings The common piston rings now play the roles of sealing, oil control, heat conduction and guiding (supporting), and are generally composed of three parts. The surface of the first gas ring is chrome plated, because of the harsh working conditions and high hardness, and the edge of the ring body is barrel surface, which has the function of sealing the cylinder pressure; The second gas ring is a conical piston ring. Compared with the first ring, the working environment is slightly better. However, if it is not installed correctly, it will cause the engine oil to run and cause the phenomenon of burning engine oil. The oil ring plays a sealing role, and at the same time, it will store excess engine oil and recycle it through the oil return hole on the piston. 2. Inspection method of piston ring After removing the cylinder block, place the piston ring at 2/3 of the cylinder block and measure the opening clearance. For example, the standard value of piston ring opening in HK250 is 0.03 ~ 0.08 mm If it exceeds this value, it proves that the piston ring is seriously worn and needs to be replaced with a new one. 3. Wear of the Piston When the piston reciprocates in the cylinder, it needs oil to lubricate between the two friction surfaces. If there are foreign objects or lack of oil, it will cause wear on the metal surface. When the wear exceeds the standard value, it will cause oil burning. 4. Measurement method of piston First, clean the piston and cylinder, and measure the slightly top position of the piston skirt with vernier caliper (this place is the most worn). If the measured data exceeds the standard value, it is necessary to replace the new piston; If there is no vernier caliper, you can push the piston into the cylinder and check the clearance between the piston and the cylinder with a feeler gauge. When the standard value is exceeded, a new piston needs to be replaced. If the clearance between the new piston and the cylinder exceeds the standard, it is necessary to replace the new cylinder to solve the oil burning phenomenon. Brief introduction of valve group The valve oil seal is a sealing ring installed on the valve stem, which can prevent the oil from flowing into the combustion chamber along the valve stem. Under the action of the spring, the valve is in close contact with the valve seat, but from the microscopic point of view, the two contact surfaces are not seamless and need to be polished before use. When the valve and valve seat are professionally and complex polished, a circle of bright dark gray will be formed, which is the valve sealing belt. When the valve is closed, the gas in the combustion chamber will not leak through the valve, thus ensuring the stability of the cylinder pressure. The judgment method of burning engine oil is to judge whether there is burning engine oil in your car. Without disassembling the engine, first measure the cylinder pressure with the cylinder pressure gauge, and you can preliminarily judge the general reason of burning engine oil. (It is suggested to start the engine to measure the cylinder pressure first, so that the engine can reach the normal working temperature; The electric starter should ensure that the battery voltage is sufficient and the starter works well. The most important thing is to make the throttle fully open. Only in this way can the accuracy of cylinder pressure measurement be guaranteed. For example, the normal cylinder pressure of HK250 is 9. 1~ 14kg/cm2. If the cylinder pressure is just within the standard range, it is necessary to check whether there are other reasons for burning oil. See the contents mentioned by abnormal factors for details. If the cylinder pressure is low, there is usually oil burning. Engine oil combustion usually has two vehicle states, cold engine oil combustion and continuous engine oil combustion. When the vehicle starts, the exhaust pipe emits blue smoke, and the blue smoke disappears after the cylinder temperature rises. Like normal vehicles, there is nothing unusual in the color of the exhaust gas, but if you smell it carefully, you can smell a heavy mixture of gasoline and engine oil in the exhaust gas. This situation is that the engine oil is burned in the cold car, which is generally due to the wear of the cylinder block, piston and piston ring, which leads to the increase of the gap. When the engine continues to emit blue smoke after the temperature rises, it is necessary to check the wear of valve components, especially the valve oil seal. If the oil seal is damaged or the inner diameter is out of tolerance, it must be replaced; At the same time, when replacing the oil seal, check whether the valve stem diameter exceeds the limit value. If the gap between the new oil seal and the old valve stem is greater than the standard value, the valve should also be replaced. Treatment of oil burning 1. We said before replacing the piston ring that 60 ~ 70% of the common oil burning is caused by the wear of piston parts. First of all, we must ensure that the accessories used are produced by qualified regular manufacturers, and also pay attention to whether the cylinder diameter of the repaired engine is increased. Usually, there is a mark on the piston ring. If there is 025, it means that the cylinder diameter has been enlarged and needs to match the enlarged piston ring. Even if a new piston ring is fitted, the opening clearance should be measured. Too much clearance will affect the cylinder pressure, and too little clearance will pull the cylinder. Pay special attention to this point. 2. Replacement of the valve oil seal Except for the piston assembly, most of the burning oil is caused by the aging of the valve oil seal, so it is necessary to remove the cylinder block, press down the valve spring with a special tool, remove the valve lock piece, and check the sealing conditions of the valve oil seal and the valve sealing belt. If the valve oil seal is damaged or cracked, a new product must be replaced. This is to remind everyone that they must buy factory accessories. After all, it is very complicated to dismantle it once. If there is a derivative failure due to the quality problem of the accessories, it will not be worth the candle. 3. Grinding valve sealing tape is an important guarantee to ensure valve sealing. Once the valve sealing belt is burnt or stuck by foreign matter, it will lead to lax sealing, which will cause engine oil to burn and seriously affect the starting performance. So the faulty valve should be ground. First, grind the valve seat with a reamer. After the rough grinding is completed, use 80 mesh grinding paste to finally run in the valve until a circle of sealing tape can be clearly seen. Finally, draw a few vertical lines evenly on the valve with a pencil, and then install it on the ring seat for rotation. If the vertical channels are divided neatly, it proves that the sealant tape has been polished successfully and can be assembled. If the valve band is narrow or the valve edge is thin, it is necessary to consider replacing it with a new valve assembly to ensure sealing. 4. Drill the cylinder and enlarge the piston assembly. If the cylinder bore strain is large, check the oil pumping capacity of the oil pump first, because the oil pressure is too low, which will also cause serious strain. Secondly, check whether the oil circuit is blocked, especially the oil circuit of crankshaft and connecting rod. If the oil supply is insufficient, it is easy to tighten the new joint again. If the cylinder liner has been seriously worn, it is necessary to bore and grind the cylinder liner, with the maximum increase of three levels. If the boring amount is too large, it will cause excessive load to crankshaft, connecting rod and other parts, produce extremely high heat, and affect the life of the whole machine. So it is not recommended to deal with too many boring cylinders. In addition, it should be noted that after the cylinder liner is enlarged, the piston assembly with the same order of magnitude should be matched. In fact, the reason for burning engine oil has already been mentioned above. As long as we maintain good driving habits, check the amount of oil before driving, keep the habit of hot driving, and pull from time to time, it will generally not cause the phenomenon of burning oil; Even if the oil is treated earlier, it may be possible for me to change a pair of piston rings for tens of dollars, and changing the piston rings is only a middleweight repair, which will not have much impact on the whole engine, so don't worry too much. If you have some practical ability, you can solve it by yourself.