What causes the cylinder liner of the diesel engine to break?

Diesel engine cylinder liner fracture analysis:

Cylinder liners occur when cracks occur during use. Normally, the cracks in the cylinder liner are elongated. Starting from the cylinder liner flange (for example, the 6105 diesel engine), it will expand below the piston ring movement area. Cylinder liner crack (take 4135 as an example) from the bottom of the cylinder liner flange, through the cylinder sleeve flange section straight through the upper part. In addition to the partial failure of the cylinder liner, the 490 diesel engine, for example, sometimes "brushing table" Accident. That is, at the shoulder of the upper part of the cylinder liner, it is neatly broken. Take out the broken cylinder sleeve, it can be seen that the fracture is between the cylinder sleeve shoulder and the upper installation belt, and the crack extension causes the cylinder sleeve to be broken into two halves.

What causes the diesel cylinder liner to break as follows:

There are various types of cylinder liners, dry and wet, which cause the cylinder liner to break. The reasons for some actual occurrences are summarized as follows.

1 The amount of protrusion is too high. Take the 6105 diesel engine as an example. After the cylinder is set into the cylinder block, the groove plane of the cylinder liner should be slightly higher than the cylinder block plane to ensure the tightness after pressing the cylinder head gasket. High, after tightening the cylinder head, it is easy to squeeze and crack the cylinder sleeve step. Under normal circumstances, this value should be controlled within the range of 0.05-0.20mm.

When installing the cylinder liner, in order to avoid this factor, the cylinder liner is broken. It is not necessary to install a waterproof rubber band on the outer wall of the cylinder liner beforehand, and put it into the cylinder block, and carefully measure the size of each cylinder liner above the plane of the cylinder block. If it is not suitable, you can adjust the position of each cylinder sleeve to make it as flat as possible. If it is still too low after the position change, you can find an old cylinder head to disassemble, cut the copper skin into a gasket, and put it on the cylinder sleeve shoulder. The lower part is raised. If it is too high, the shoulder plane of the cylinder block can be milled to increase the shoulder depth.

2 The shoulder plane of the cylinder liner or the bearing surface of the cylinder block is not perpendicular to the center line of the cylinder. Take the 4135 diesel engine as an example. In this case, the cylinder is set into the cylinder block, and the lower plane of the step will be placed on the bearing surface of the cylinder block. The other side is suspended. Therefore, if the cylinder head nut is tightened, it will easily cause the cylinder liner to break.

3 Misuse of cylinder liners 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 The cylinder liner and the cylinder sleeve bearing hole are improperly matched. The 4102BQ diesel engine is taken as an example. The cylinder liner is a thin-wall dry cylinder liner. Its thickness is only 1.5mm, which is quite thin and is the upper cylinder positioning cylinder liner.

The cylinder liner of the diesel engine and the bearing sleeve of the cylinder sleeve are in a transitional fit. The value should be -0.03~-0.Olmm. If the cylinder liner is assembled, the cylinder sleeve and the cylinder sleeve bearing hole are too tightly fitted, and the cylinder sleeve is pressed into the bearing hole. It will be broken. At this time, it is usually found that the cutter is broken under the support shoulder of the cylinder liner. On the contrary, if the fit is too loose (the gap between the two is more than 0.003mm), there may be a gap between the cylinder liner and the socket bore. There is a gap, which leads to poor local heat transfer. It may cause thermal cracking of the cylinder liner over time.

This is because if the cylinder sleeve and the bearing hole are loosely fitted, the cylinder sleeve will oscillate laterally due to looseness in the bearing hole. Therefore, the cylinder liner is easily broken. When the diesel engine is running at high speed, the piston rod set is made. Reciprocating motion, the lateral oscillation of the piston will cause lateral vibration of the cylinder liner, increasing the vibration frequency and amplitude of the cylinder liner. Since the cylinder liner is subjected to the pressure of the combustion gas for a long time, the inertial force of the piston, the pressure of the piston ring, the vibration of the piston and The force generated by the knocking of the cylinder wall, these forces generally tend to increase the lateral force of the cylinder liner and transmit it to the cylinder sleeve bearing hole, so that the outer diameter of the cylinder sleeve and the cylinder sleeve bearing hole generate a stress stroke. The long-term operation under such alternating pressure conditions will eventually lead to fracture of the cylinder liner due to overwhelming stress.

5 Reconstruction of 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. For this reason, some 6105QC diesel engine users are in the 6105QC type in order to improve the power and economy of the diesel engine. On the basis of the 6105QC type is converted into a 6108Q diesel engine.

This is because some people simply think that the Model 6108Q is a cylinder-expanding product of the 6105QC diesel engine, so it can be upgraded by simply replacing the cylinder liner, piston, piston ring, piston pin, cylinder head gasket and other components of the 6108Q diesel engine. It is 6108Q diesel engine. As everyone knows, the assembly dimensions of the cylinder liner and cylinder block of 6108Q and 6105QC are different. Because the upper positioning flange of the cylinder liner of 6108 diesel engine is larger than Imm of 6105QC, the cylinder sleeve is pressed against the hole of the cylinder liner. It is possible to press the cylinder liner to the fracture. Even if the cylinder liner can smoothly press the cylinder sleeve bearing hole, after the diesel engine is working too high, the upper flange portion of the cylinder liner will not be able to dissipate heat due to the tight fitting. Cause the cylinder liner to break. Therefore, do not blindly modify the substitute.