After riding a motorcycle for a period of time, many motorcycle friends will feel that their mount power is reduced, and fuel consumption is increased, one of the reasons is that the gap between the piston, piston ring and cylinder is increased, resulting in a reduction in the compression ratio.

At this time, some motorcycle friends and some repair personnel will coincidentally first think of replacing the piston and piston ring method to increase sealing, improve engine power, reduce fuel consumption. This repair method is feasible in the case that the amount of cylinder wear is not too large (within the limit size), but if the cylinder wear is serious or quite serious, only by replacing the piston and piston ring (or replacing the increased piston and piston ring) often does not help, at the same time, the engine will also produce a "rattling" piston ring sound. Because in the case of normal wear, the wear amount of each part of the cylinder is very uneven, the part where the side pressure generated by the piston on the cylinder is large, the maximum wear part is usually 10 ~ 20mm down the top of the cylinder, and the cylinder of the Yangtze River 750 series engine is 20 ~ 25mm, that is, when the piston is located at the top dead center, the wear amount of the cylinder is very large. Slightly lower relative to the first piston ring.

The direction of wear parallel to the cylinder inner wall and the piston pin is smaller than the direction perpendicular to the piston pin, resulting in roundness and taper error, after the new part, can not be tightly fitted with the cylinder inner wall that is seriously out of round, so it can not increase the sealing effect. In addition to the part of the upper cylinder that the first piston ring cannot reach is extremely light wear, the piston reaches the bottom dead center when the last piston ring is located below the wear is also light, which forms the shoulder in the cylinder, and after the new part is replaced, it will impact with the shoulder in the cylinder, resulting in the piston ring. The correct repair method is that when the inner wall of the integral cylinder of alloy cast iron and the compound cylinder with alloy cast iron cylinder liner is seriously worn, the repair method of boring the inner wall of the cylinder is usually adopted. Cylinder boring and grinding size can be calculated from the following formula, that is, D repair =D+P (D is the diameter of the maximum wear of the cylinder, P is the boring and grinding processing allowance, generally 0.1 ~ 0.2mm).

After calculating the D repair value, select the closest but larger boring size for boring. The dimensional tolerance of the repaired cylinder inner diameter, the cylindricity and roundness tolerance of the inner diameter, and the surface roughness of the inner wall shall be the same as the standard cylinder technical requirements. For the chromium-plated monolithic cylinder on the aluminum alloy surface, when the inner wall is seriously worn, the repair method of inset cylinder liner is usually used, and this repair method does not need to choose a larger size piston, so it is also suitable for some imported cars that lack accessories. The specific practice is to first bore the inner diameter of the original cylinder by 5 ~ 7mm, the outer diameter of the cylinder liner and the inner diameter of the cylinder after boring using an interference fit of 0.046 ~ 0.086mm, the cylinder liner should be opened and the cylinder position of the same air port, and the corresponding air port on the cylinder should be aligned after pressing. The cylinder liner is then honed to meet the dimensional tolerances, shape tolerances and surface roughness requirements of the standard cylinder (cylinder liner is made of high phosphorus wear-resistant cast iron or other wear-resistant cast iron).

After repair by the above two repair methods, the cylinder with an air port on the cylinder wall should also be scraped and polished on the edge of each air port to prevent the piston ring from colliding with the edge of the air port. After this repair, and then replace the corresponding size of the piston and piston rings, your beloved mount will be restored to the vitality it should have before.

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