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diesel engine cylinder liner fracture analysis:

　　Cylinder linerIn the use of cracks in the failure occurs, usually the cylinder liner cracks in the longitudinal shape. Starting from the cylinder liner flange (in the case of a 6105 diesel engine), it extends below the piston ring movement area. Some cylinder liner cracks (take 4135 as an example) start from below the cylinder liner flange and pass through the cylinder liner flange section to the upper part. In addition to the cylinder liner will produce local fracture failure, to 490 diesel engine, for example, sometimes there will be "brush table" accident. That is, at the upper shoulder of the cylinder liner, a neat fracture occurs. Take out the broken cylinder liner, it can be seen that the fracture is between the shoulder of the cylinder liner and the upper mounting belt, and the extension of the crack breaks the cylinder liner in half.

What causes the diesel engine cylinder liner fracture is as follows:

Cylinder liners are divided into dry and wet types. There are many reasons for cylinder liner fracture. Some actual reasons are summarized as follows.

1 The amount of protrusion is too high. Take a 6105 diesel engine as an example. After the cylinder liner is installed in the cylinder block, the stop plane of the cylinder liner should be slightly higher than the plane of the cylinder block to ensure the sealing performance after pressing the cylinder head gasket. However, if the amount of protrusion is too high, after tightening the cylinder head, it is easy to squeeze and crack the cylinder liner step. Under normal circumstances, this value should be controlled in the range of 0.05-0.20mm.

When installing the cylinder liner, in order to avoid this factor causing the cylinder liner to break, it is not necessary to install a waterproof rubber ring on the outer wall of the cylinder liner in advance, but put it into the cylinder body, and carefully measure the height of each cylinder liner above the plane of the cylinder block. size. If not, can be each cylinder liner transposition adjustment, as far as possible to make it flat. If it is still too low after the transposition, you can find an old cylinder gasket to disassemble, cut the copper skin into a gasket, and pad it on the lower part of the cylinder liner shoulder to raise it. If it is too high, the shoulder plane of the cylinder block can be milled to increase the shoulder depth.

2 The cylinder liner shoulder plane or the pressure-bearing surface of the cylinder block is not perpendicular to the cylinder centerline. Take a 4135 diesel engine as an example. In this case, if the cylinder liner is installed into the cylinder body, one side of the lower plane of the step will be on the pressure-bearing surface of the cylinder block., The other side is hanging in the air. Therefore, once the cylinder head nut is tightened, it is easy to cause the cylinder liner to break.

Take 6105Q diesel engine as an example. At present, there are 9 variants in China, but there are only 6 types of cylinder liners, as shown in Figure 2-8.

4 Improper matching of cylinder liner and cylinder liner bearing hole Take 4102BQ diesel engine as an example. The cylinder liner is a thin-walled dry cylinder liner with a thickness of only 1.5mm, which is quite thin and is an upper stop positioning cylinder liner.

The diesel engine cylinder liner and cylinder liner bore for transition fit, this value should be -0.03 ~-0.Olmm. If the cylinder liner is fitted with the cylinder liner bearing hole too tightly, the cylinder liner will break when it is pressed into the bearing hole. At this point, it is usually found in the cylinder liner support shoulder under the knife fracture. On the contrary, if the fit is too loose (the gap between the two is greater than 0.003mm), there may be a gap between the cylinder liner and the cylinder liner bearing hole, resulting in poor local heat transfer, and the cylinder liner may be thermally cracked over time.

This is because if the fit between the cylinder liner and its bearing hole is too loose, the cylinder liner will swing laterally in its bearing hole due to looseness. Therefore, the cylinder liner is easy to break. When the diesel engine is running at high speed, the piston connecting rod group reciprocates, and the lateral swing of the piston will cause the lateral vibration of the cylinder liner, which increases the vibration frequency and amplitude of the cylinder liner. Because the cylinder liner bears the pressure of the combustion gas, the inertial force of the piston, the pressure of the piston ring, the vibration of the piston and the force generated by the knock on the cylinder wall for a long time, these forces generally tend to increase the lateral force of the cylinder liner and transmit it to the cylinder liner. The bearing hole of the cylinder liner causes a stress strike between the outer diameter of the cylinder liner and the bearing hole of the cylinder liner. The cylinder liner works under this alternating pressure for a long time, and eventually the cylinder liner will break due to overburden.

5 The 6108Q diesel engine produced by Guangxi Yulin diesel engine is a replacement product developed on the basis of inheriting many advantages of the 6105QC diesel engine of the factory. To this end, some 6105QC diesel engine users in order to improve the power and economy of the diesel engine, based on the 6105QC type, the 6105QC type converted into 6108Q diesel engine.

This is because some people simply believe that the 6108Q is a cylinder expansion deformation product of the 6105QC diesel engine, so you only need to replace the cylinder liner, piston, piston ring, piston pin, cylinder gasket and other related parts of the 6108Q diesel engine. Upgrade to 6108Q diesel engine. As everyone knows, 6108Q and 6105QC cylinder liner and cylinder block assembly size is not the same. Because the upper positioning flange of the 6108 diesel engine cylinder liner is Imm larger than 6105QC, when the cylinder liner is pressed into the cylinder liner bearing hole, the cylinder liner may be pressed to fracture. Even if the cylinder liner can smoothly press the cylinder liner bearing hole, after the temperature of the diesel engine is too high, the upper flange part of the cylinder liner will be unable to dissipate heat due to the tight fit, which will eventually cause the cylinder liner to break. Therefore, must not blindly refit substitute.