Because of the bad working conditions of the piston ring, it is not only to bear the mechanical load and heat load produced by combustion chamber gas combustion, but also to have relative friction movement with the cylinder wall and piston ring trough due to high and lower speed movement, and the wear and elastic strength of the piston ring will be gradually weakened. The deterioration of the technical status of the piston ring will inevitably affect its performance. Therefore, we need to find out the deterioration of the piston ring technology in order to improve the performance of the engine. The technical status of piston rings can be determined by the following tests. The end gap (or opening gap) of the piston ring refers to the gap between the two ends of the piston ring opening at the opening of the piston ring to prevent the piston ring from being stuck in the cylinder after the piston ring is heated and expanded. When measuring the end clearance of the piston ring, the opening gap of the piston ring can be determined for measuring the upper and lower parts of the cylinder wall for the standard new cylinder. For the used and unprocessed cylinders, the cylinder gauge is used to check whether the taper and ellipticity of the cylinder are out of limits. If the cylinder does not exceed the limit, the piston ring opening gap should be selected and the most suitable standard should be selected according to the location of the piston ring at the bottom part of the cylinder stroke. When measuring, the selected piston ring is put in the cylinder after boring, and the prescribed thickness gauge is inserted into the piston ring opening. The standard clearance standard is 0.25 ~ 0.45 mm for each 100 mm cylinder diameter. If the clearance is too large, it is easy for the cylinder to leak. If the gap is too small, when the piston ring is heated, the expansion will die in the cylinder or cause the phenomenon of the cylinder. It is necessary to file the end face with a file, and then the port is chamfered so as not to scrape the cylinder. The piston ring backlash refers to the clearance between the piston ring and the piston ring groove after the piston and piston ring are loaded into the cylinder. For measuring convenience, the difference between groove depth and ring width is usually calculated. The gas ring of the gasoline engine is generally lower than 0.35 mm on the shore, that is to say, the second is to prevent the ring from being stuck in the cylinder, if the backlash is too small, the piston ring groove can be turned. The piston ring backlash refers to the clearance between the piston ring and the piston ring groove. Large clearance will affect the sealing effect, such as small side clearance is easy to be stuck. When measuring the side gap, the piston ring is installed in the ring groove. It is suitable for the ring groove to roll not to be loose and not to be astringent. Then the gap between the ring and the slot is measured with a thickness gauge. When the piston ring clearance is too small, the piston ring can be leveled and lapping to achieve the required backlash. (1) it is better to measure on condition of elasticity. The opening of the piston ring is in a horizontal position, and when it is compressed to the standard opening gap, the elastic force should be within the specified value range. (2) use hand to test the elasticity of opening direction and torsion direction. The opening direction test is to compress the piston ring with the appropriate force to make the opening ends meet (or open the opening of the ring to double the original opening) and then relax. If the elasticity is good and not deformed, the elastic force of the piston ring is qualified; if the plastic deformation of the ring is more than 15% of the original opening, it shows that the ring is a inferior product and can not be used. The torsional direction test is that the opening ends of the ring are staggered at a distance, and if it can be automatically reduced after relaxation, it shows that the elastic force of the piston ring is good and can be used. Be careful not to overexert yourself in the examination, nor to strain too much. Otherwise, the piston ring will be broken. (3) use the contrast method. The piston ring and the new piston ring are erected together, the ring mouth is facing to the side and is in a horizontal position, and the hand is pressed down from the top. If the end face of the piston ring is closed, and the end face of the new piston ring has a certain distance (or a certain gap), it indicates that the measured piston ring's elastic force has been weakened. The larger the gap between the two openings, the weaker the elastic force of the tested piston ring. The measured piston ring is placed in the standard cylinder sleeve, the lamp holder with the lamp holder and the switch is installed in the bottom of the cylinder sleeve hole, the shading board is covered on the piston ring, the circuit is connected, and the leakage gap between the ring and the cylinder wall is observed. The requirement of piston ring leakage of general diesel engine: no more than two leaks in the whole circle; no light leakage is allowed within the 30 degree range of the opening of the distance ring; the width of the light gap in the leakage is not more than 0.03 mm, and the angle of the center of the light gap can not exceed 30 degrees. The surface of the piston ring and the upper and lower ends of the piston ring groove are the second sealing covers of the ring. The sealing surface will not cause leakage, so the flatness of the surface of the piston ring should be checked. There are two kinds of inspection methods: one is to use a special equipment, that is to use two parallel plates with very high surface roughness, the distance between the thickness of the checked ring and the allowable warping range of 0.05 mm, when the loop can pass the distance without damping, otherwise it is not qualified; the other is a simple method to put the ring free flat in flat. On board, inspect its contact or plane leakage condition and decide whether to adopt it.