Overhaul Process for 6BT Series Engine of 250KW Cummins DG Set

The performance of 6BT series engine of 250KW Cummins diesel generator is not bad before the overhaul, but after the overhaul according to the traditional method, the performance of most of the engines will be greatly reduced. Most of them are lack of power due to the early abnormal wear of the cylinder block within 30000 km. There are gas blowby, oil blowby and oil burning, sometimes accompanied by a slight "cylinder pulling" phenomenon.

What should we pay attention to in overhaul process and materials of 250KW Cummins DG Set?

1.Because the cylinder block of Cummins 6BT engine is relatively expensive, we still adopt the traditional overhaul process plan of boring the cylinder and not replacing the cylinder directly. But the cross small flat top honing process is adopted in the finishing of cylinder bore according to the requirements. This is helpful to the oil storage when the cylinder liner works and improves the wear resistance of the friction pair.

2.Piston ring, specially the first piston ring must be qualified. We can judge by checking if there is a layer of porous chrome plating on the outer surface of the first piston ring, which is dark on the eyes and bumpy on the hands. The hardness of porous chromium plating is very high, and a small amount of engine oil can be stored, so as to improve the lubrication conditions and increase the service life by 2-3 times.

3.We should use high quality piston. The inferior piston produced by some manufacturers will have various faults when it is installed in the engine, so it can not be used normally.

4.The cylinder block of Cummins 6BT engine is dry cylinder liners, but when changing cylinder liners, it is not enough to pull out the old cylinder liners and press in the new cylinder liners as the traditional ones. Instead, it is necessary to first punch the bottom hole of the cylinder block according to the specified size and leave a stop, and then adopt the following process for press mounting:

a.Put the cylinder liner into the refrigerator and cool it to -20℃ for more than 1h;

b.After the cylinder line is cooled, we can coat loctite 620 glue on the inner surface of each cylinder hole, which has the characteristics of high temperature resistance, corrosion resistance and effective protection of the interference fit between the cylinder block and the cylinder liner.

c.Wear protective gloves with both hands, and press the frozen cylinder liner (the outer diameter is reduced by 0.05-0.07mm, and the interference between the cylinder block and the cylinder liner is 0.05-0.08mm) into the cylinder hole;

d.Beat the cylinder liner lightly with the special tool to make it fully contact with the lower lip surface of the cylinder block.

When pressing the cylinder liner, if not adopted the above process, while first bore the bottom hole of the cylinder block according to the specified size and then press the cylinder liner directly in, this will result in different degrees of shrinkage of the cylinder liner. After some engines are used, the cylinder liner moves in the bottom hole of the cylinder block, resulting in a gap between the cylinder liner and the bottom hole of the cylinder block and poor engine cooling. This is also one of the main reasons for the early abnormal wear of Cummins 6BT engine cylinder block within 30000 km after the traditional overhaul.

What should we pay attention to when replacing cylinder block?

There are fake and inferior cylinder block of Cummins 6BT engine in the market. When replacing the cylinder block, we must pay attention to it. Although it is generally unable to judge its quality from the material, it can be judged whether its quality is qualified by measuring the shape tolerance of the cylinder barrel, camshaft seat hole and other relevant apertures to judge whether it meets the requirements.

In addition, although the piston of Cummins 6BT engine is the same as that of many other heavy-duty vehicles, the piston is cooled by the pressure lubricating oil flow through the piston cooling nozzle set above the main bearing. However, the cooling nozzle is not as long and obvious as that of other cars, but is hidden above the main bearing like a grease nozzle, which is not easy yo notice or see generally.

Therefore, when replacing the cylinder block, it is easy to miss the piston cooling nozzle on the new cylinder block, resulting in the failure of low engine oil pressure. We should pay attention to this problem when replacing the engine block.

What should we pay attention to when removing and replacing the camshaft?

There is no bushing between the second and seventh camshaft seat holes of Cummins 6BT engine block and camshaft when they are matched. On the premise that the material of camshaft must be the required chilled cast iron. During operation, both the shaft and the hole wear are very little. Generally speaking, the cylinder block and the axle 2 will not need to be replaced due to the wear of the six friction pairs during the whole service life of the engine.

Do not buy and use camshaft made of cast steel, otherwise the cylinder block will be scrapped due to serious wear of camshaft journal support hole of cylinder block.

When the first camshaft seat hole of Cummins 6BT engine block is matched with the camshaft, there is a bush between them. Because of this unique design, it is easy to miss the first bushing when disassembling the camshaft.

When replacing cylinder head of Cummins 6BT series engine, we must pay attention to use qualified product.

It is normal that diesel generator set needs to overhaul, as long as we use correct overhaul process and materials, the faults will be solved effectively, ensuring smooth start-up, as well as safe and reliable operation of the unit.

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