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Reasons For Cracks In Diesel Generator Cylinder Block And Cylinder Head

Sep. 05, 2023

Cracks, plane deformation, corrosion of water channels, damage to screw holes, etc. will appear in different positions of diesel generator cylinder and cylinder head. The parts of the engine where cracks appear in different forms have certain rules, and the parts where cracks occur also have certain rules. Generally speaking, the reasons for the formation of cracks are no more than three aspects.


1. Inadequate design and manufacture.

(1) Part of the improved engine is a reinforced type, and the speed and power are significantly higher than the original engine. When running at high speed, the inertial force and stress of the engine also increase, which is prone to cracks.


(2) The cylinder structure is complex, the wall thickness is uneven, and some weak parts have low rigidity and are easy to crack.


(3) Stress concentration will occur in the processed parts and unprocessed parts. The inner wall thickness of the transition section will cause stress concentration. When these stresses are superimposed with the deactivated residual stress, cracks are prone to occur.


2. Improper use.

(1) In the cold winter, antifreeze is not used, or the cooling water is not discharged in time after the shutdown, causing the cooling water in the water jacket to freeze, or in the severe winter, the freezing crack is caused by adding high temperature water.


(2) In the case of high temperature, the internal combustion engine suddenly adds cold water, causing excessive thermal stress on the cylinder block and cylinder head, resulting in cracking of the cylinder and cylinder head.


(3) Careless in the process of disassembly or operation, the cylinder or cylinder head is severely shaken or collided and cracks appear.


(4) When the material is in operation, the thermal stress generated is too large. For example, the internal combustion engine is overloaded for a long time, which leads to an increase in the stress in the cylinder, the scale in the water jacket is too thick, which reduces the cooling water passage area, and the heat transfer capacity of the scale is low, which reduces the heat dissipation performance of the engine, especially in the cylinder. Between the valves, and the water channels near the intake and exhaust ports are blocked, which seriously affects its heat dissipation, causing the local working temperature to rise. Too high temperature stress leads to cracks.


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(5) When the heater is insufficient, the load increases sharply, resulting in serious uneven heating and cooling changes in the cylinder block and cylinder head, resulting in cracks.


3. Poor quality of maintenance.

Diesel generator sets and maintenance, the process requirements are not strictly implemented. If the cylinder head nuts are not tightened in the specified order and torque. The tightening force is uneven, and the cylinder head nut that does not meet the requirements is used, when assembling the valve seat ring, if the appropriate excess pressure is not selected, such as selecting the appropriate material and machining accuracy, it will also cause cracks.


Tighten the cylinder head nut, use a torque wrench with accurate readings, and press the middle first, then the middle, and the score is 2-3 times (for example, the specified torque of the cylinder head nut of the 135 series diesel generator is 245-265N.m, the first torque to 10N.m, the second time to 20N.m, the third time can be screwed to the specified torque) symmetrically tightened to the specified torque. After the engine with the reassembled cylinder head fires for the first time, the cylinder head nut should be tightened again according to the above requirements to achieve the specified torque, and the valve clearance should be readjusted after the engine cools down.


Friendly reminder: The order of removing the cylinder head nuts is just the opposite of the above order. In the order of the two sides first and then the middle, loosen them symmetrically in 2-3 times. Never remove a screw cap all at once for convenience.


Cracks in the cylinders and cylinder heads of diesel generators may cause coolant leakage or oil leakage, affect the work of the internal combustion engine, and even make the cylinders and cylinder heads scrapped. Therefore, it is very important to learn to analyze and properly maintain and maintain the cylinder and cylinder head.


Three detection methods for diesel generator cylinder head and cylinder head cracks:

Cracks are not allowed in the cylinders and cylinder heads of diesel generators, otherwise the internal combustion engine will not work properly. In general, it is easy to find serious cracks in the cylinders and cylinder heads, but it is difficult to observe small cracks. In general, the detection methods for cylinder and cylinder head cracks are as follows.


1. Hydraulic method.

According to the technical requirements, put the cylinder head and cylinder head gasket into the cylinder body according to the technical requirements of the cylinder, and connect the outlet pipe joint of the press with the front end of the cylinder. Next, keep the pressure at 0.3~0.5MPa in the cylinder block and cylinder head (if possible, use hot water at 80~90℃), and no leakage will occur within 5 minutes. If water droplets seep out, it means there is a crack. After repairing the cylinder block, replacing the cylinder liner, valve seat ring and valve pipe, a hydraulic inspection should be carried out.


2. Air pressure method.

If there is no hydraulic device, tap water, air pump or air cylinder can be used. Inject water into the cylinder block and cylinder head, and then use an air pump or an air pump to fill the water jacket with water, and use the gas pressure to check whether there is liquid leakage, and you can determine where the crack is. Install a one-way valve at the connection between the cylinder and the cylinder to prevent the backflow of water and air.


3. Hammer immersion oil display method.

When the conditions of the above two inspection methods are not met, the oil hammer display method can be used. When checking, first soak the parts in diesel or kerosene, soak them on the oil surface for a certain period of time, apply a layer of white powder, and then tap the non-working surface lightly with a hammer. If there is a crack, diesel or kerosene will penetrate into the crack due to vibration, making the white line at the crack a yellow line. Check whether the cylinder block or cylinder head has cracks, which should be repaired in time.


Guangxi Dingbo Generator Set Manufacturing Co.,Ltd. is a manufacturer of professional generators, diesel generator sets, non-moving generator sets, Cummins generator sets, Volvo generator sets, etc. It has 64 sales and service departments across the country, providing users with design, supply, debugging, and maintenance at any time. Welcome customers to come to consult and visit. Looking forward to your inquiry, please send email to us for details sales@dieselgeneratortech.com

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