Put a few drops of oil on the filter test paper, and take a clean red filter test paper. After the lubricating oil leaks, if there is black powder on the surface, and there is a sense of resistance to the touch, it means that there are many impurities in the lubricating oil. A good lubricating oil has no powder, and it is dry and smooth to the touch with yellow marks. Grease is very critical if, in the process of using the bearing. The use of degenerated grease will not only fail to function as it should, but will also damage the bearing. ① One of the oil flow observation methods contains the lubricating oil to be checked, and two measuring cups are taken. Put the other empty on the table, lift the measuring cup full of lubricant 30-40 cm away from the table and tilt it to let the lubricant slowly flow into the empty cup, observe its flow, good quality lubricant oil flow It should be slender, uniform, and continuous from time to time. If the oil flow is suddenly fast and slow, and sometimes large chunks flow down, it is said that the lubricating oil has deteriorated. ② The lubricating oil with better hand-twisting method feels lubricating, less wear debris, and no friction. Twist the lubricating oil between the thumb and index finger for repeated grinding. If you feel a large frictional sensation such as sand particles between your fingers, it indicates that there are too many impurities in the lubricating oil and cannot be used anymore. Replace with new lubricating oil. ③ In the light method, use a screwdriver to lift up the lubricating oil on a sunny day. Make a 45-degree angle to the horizontal. Contrast with sunlight and observe the condition of oil droplets. Under sunlight, it can be clearly seen that there is no wear debris in the lubricating oil as good and can continue to function. If there are too many wear debris, the lubricating oil should be replaced.