Causes of cylinder liner fracture of second-hand semi-trailer

Cracks often occur in the cylinder liner of second-hand semi-trailer in use. Generally, the cracks in the cylinder liner are longitudinal. Starting from the cylinder liner flange (take 6105 Diesel engine as an example), it will expand below the moving area of the piston ring. Some cylinder liner cracks (take 4135 as an example) start from below the cylinder liner flange, pass through the section of the cylinder liner flange and go straight to the upper part. In addition to local fracture failure of the cylinder liner, taking 490 diesel engine as an example, sometimes "brush table" will appear accident. That is, neat fracture occurs at the shoulder on the upper part of the cylinder liner. 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. The extension of the crack breaks the cylinder liner into two halves.

The cylinder liner can be divided into dry type and wet type. There are various reasons for cylinder liner fracture. Some actual reasons are summarized as follows:

(1) the protrusion is too high. Take 6105 Diesel engine as an example. After the cylinder sleeve is inserted into the cylinder block, the stop plane of the cylinder sleeve should be slightly higher than the plane of the cylinder block to ensure the tightness after pressing the cylinder. However, if the projection is too high, it is easy to squeeze and crack the steps of the cylinder liner after tightening the cylinder head. Generally, this value shall be controlled within the range of 0.05 ~ 0.20mm.

When installing the cylinder liner, in order to avoid the fracture of the second-hand semi-trailer cylinder liner caused by this factor, 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 dimension of each cylinder liner above the plane of the cylinder block. If it is not appropriate, each cylinder liner can be transposed and adjusted to make it as flat as possible. If it is still too low after transposition, find an old cylinder to disassemble, cut the copper sheet into a washer and pad it under the shoulder of the cylinder liner 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 shoulder plane of cylinder liner or the pressure bearing surface of cylinder block is not perpendicular to the cylinder centerline. Take 4135 diesel engine as an example. In this case, if the cylinder is sleeved into the cylinder body, it will appear

One side of the lower plane of the step is close to the pressure bearing surface of the cylinder block and the other side is suspended. Therefore, once the cylinder head nut is tightened, it is easy to cause cylinder liner fracture.

(3) misuse of cylinder liner take 6105Q diesel engine as an example. At present, China has 9# variant products, but the cylinder liner is only 6# type, as shown in Figure 2-8.

According to the data listed in table 2-1, the main dimensions of various cylinder liners are different. If Hunan 6105q-1 cylinder sleeve is used on Guangxi Yulin 6105QA machine, the cylinder sleeve will be broken. Similarly, the cylinder liners of Shanghai Chengfu, Guangxi Yulin, Liuzhou and Hunan 6105Q diesel engines, as well as the cylinder liners of Hunan 6105-1 diesel engines with reduced boss outer diameter, cannot be used on Guangxi Yulin 6105qafi] 6105QC engines. This is because the two cylinder liners are 10 mma8 longer than the water jacket wall of the latter 5mm, total length 10mmai2mm respectively. If these two cylinder sets are used on 6105QA and 6105QC machines in Yulin, Guangxi, firstly, the waterproof ring on the cylinder sleeve will expose the lower sealing ring belt of the cylinder block and will not play a waterproof role; secondly

The cylinder liner will be broken due to the collision of the cylinder liner when the connecting rod moves.

(4) improper matching between 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 a top dead end positioning cylinder liner.

The cylinder liner and cylinder liner bearing hole of the diesel engine are transition fit, and the value shall be -0.03 ~ -0.01 mm. If the cylinder liner fits too tightly with the cylinder liner bearing hole when assembling the cylinder liner, the cylinder liner will break when pressed into the bearing hole. At this time, it is usually found that the tool is broken at the undercut 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 0.0003mm), there may be a gap between the cylinder liner and the cylinder liner bearing hole, resulting in poor local heat transfer, and hot cracking of the cylinder liner may occur over a long time.

This is because if the fit between the cylinder liner and its bearing hole is too loose, the cylinder liner will swing laterally due to looseness in its bearing hole. Therefore, the cylinder liner is easy to break. When the diesel engine runs at high speed, the piston connecting rod group moves back and forth, and the transverse swing of the piston will cause the transverse vibration of the cylinder liner, increasing the vibration frequency and amplitude of the cylinder liner. Because the cylinder liner bears the pressure of combustion gas, the inertia force of piston, the pressure of piston ring, the vibration of piston and the force generated by knocking on the cylinder wall for a long time, these forces generally tend to increase the transverse force of cylinder liner and transmit it to the bearing hole of cylinder liner, resulting in a stress knocking between the outer diameter of cylinder liner and the bearing hole of cylinder liner. If the cylinder liner works under this alternating pressure for a long time, it will eventually break due to overburden.

(5) the 61080 ^ 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 plant. Therefore, in order to improve the power and economy of second-hand semi-trailer diesel engine, some 6105QC diesel engine users refitted 6105QC into 6108c « oil engine on the basis of 6105QC.

This is because some people simply believe that 6108q is a cylinder expansion deformation product of 6105QC diesel engine, so it can be upgraded to 6108q diesel engine only by replacing the cylinder liner, piston, piston ring, piston pin, cylinder gasket and other relevant parts of 61080 ^ oil engine. As everyone knows, the assembly dimensions on the cylinder liner and cylinder block of 6108q and 6105QC are different. Because the upper locating flange of 6108 diesel engine cylinder liner is 1mm larger than 6105qcs, it is possible to press the cylinder liner to fracture when the second-hand semi-trailer cylinder liner is pressed into the cylinder liner bearing hole. Even if the cylinder liner can be smoothly pressed into the cylinder liner bearing hole, when the temperature of the diesel engine is too high, the upper flange of the cylinder liner will not be able to dissipate heat due to too tight fit, resulting in the fracture of the cylinder liner. Therefore, we must not blindly refit and substitute.