First, only replace the plunger, nozzle, ignore the technical status of the valve. After the oil valve wears out, the residual pressure of the high pressure fuel pipe will be too high, resulting in that the fuel nozzle will not be cut off and the oil will be dripped, resulting in diesel engine exhaust smoke, knocking cylinder, and unstable operation. The method is to check the oil valve, the range of 0-600 kg / square centimeter pressure gauge detection, when the hands down from 200 kg to 180 kg / square centimeter, the pressure holding time should be greater than 15 seconds, otherwise it should replace the oil valve; or High pressure oil pipe mouth up, pump out diesel oil, make the oil level flush with the nozzle, put the throttle back to the stop position, suddenly reverse the half circle of the wheel, the high pressure oil pipe mouth is not sucked up as qualified, otherwise the oil valve should be replaced . Second, only adjust the valve clearance, ignore the valve timing. Most people only adjust the valve clearance according to the specification, but ignore the timing of checking the valve timing. Especially the aging machine, due to changes in the geometry of the cam after wear, causing the valve to open early and early closure, will lead to insufficient intake, exhaust is not clean, fuel consumption, power drop. Therefore, when adjusting the valve clearance of aged diesel engines, the valve clearance should be appropriately reduced to compensate for the valve phase error and achieve valve timing. For example, for the S195 diesel engine, each valve clearance is reduced by 0.1 mm, and the valve phase is changed by 3 degrees. However, the valve clearance can not be less than 0.2 mm, otherwise it will be affected by the expansion, which will result in lax valve closing. If the valve clearance is already 0.2 mm and the valve phase is still more than 5 degrees, the working condition of the diesel engine deteriorates significantly and the camshaft should be replaced. Third, only look at the amount of oil in the sump, neglecting the quality of oil. Many people only supplement the engine oil and never check the quality of the oil and do not replace it. As everyone knows, the waste oil that should be replaced contains a large amount of oxidized substances and metal shavings, which reduces the lubricating performance, increases the wear of the parts and shortens the service life. Therefore, the quality of the oil in the machine should be checked at any time. The general method is to grind the oil by hand. If there is mechanical impurity or insufficient viscosity, it should be replaced in time. Another inspection method is to use the used engine oil on a white paper. If the black spot is small and the color is light, the surrounding yellow color can be used continuously. If the spot is black and large, there is no yellow trace around, it should be replaced. . Fourth, only maintain the air filter, ignore the air short circuit. There are many causes of short circuit in air, for example, the air filter fixed on the tricycle frame is not welded in the inlet pipe, the gasket is not added at the joint of the air intake pipe, the air inlet pipe is inserted into the hose, the clamp is not loosened, and the intake hose is not broken. It has been found that the lack of aprons in the air filter, etc., will cause short circuits in the air, allowing unfiltered air to enter the cylinder and intensify wear of cylinders, pistons, piston rings, valves, and other mechanical parts. 5. Only clean the oil filter and ignore the cleaning of the oil chamber. Most diesel engine connecting rod journals are hollow and have oil plugs at both ends, which are called clean chambers. Lubrication oil of the connecting rod bearing under the action of centrifugal force, its impurities attached to the cavity wall, thereby improving the lubrication quality. In order to remove the oil plug every 500 hours of operation of a typical diesel engine, the impurities in the purified oil chamber and the oil passage should be removed according to the prescribed method.