Analysis and elimination of diesel engine cylinder head component deformation, pad burning and crack

1 cylinder head deformation

Cylinder head deformation mainly means that the flatness of the contact plane between the cylinder head and the cylinder block is out of tolerance, which will cause the cylinder seal not tight, water leakage and air leakage, resulting in insufficient compression force, and in serious cases, the cylinder gasket will be burned. [Jishan Huayao we media network launched]

A diesel engine combustion chamber is not well sealed, cylinder liner burning accidents occur continuously, and it is difficult to start, which can not reach the rated power. At first, it was thought that it was caused by insufficient or uneven tightening torque of cylinder head bolts, but after careful inspection, it was found that it was caused by warping deformation of cylinder head plane. It is found that the cylinder cover is too much higher than the upper plane of the cylinder block, and the height of each cylinder cover is different. It is concluded that this is the main reason for the deformation of the cylinder cover. The causes of cylinder head deformation are as follows: when the diesel engine works at high temperature, it suddenly cools down; when assembling, the cylinder head bolts are not tightened according to the specified sequence and torque, or the tightening torque is not equal; the material of the cylinder head does not meet the requirements; when the cylinder head is removed under the hot condition, it will cause the cylinder head bottom plane warping deformation.

The flatness inspection method of the contact plane between cylinder head and cylinder block is as follows: place a flat ruler on the cylinder head plane, measure the maximum value of the gap with a thickness gauge, that is, the flatness of the plane, and repair it when the flatness error of the whole length is greater than 0.15 mm.

The cylinder head deformation can be repaired by the following methods: (1) local preheating and pressure correction, combined with scraping repair plane. When the warpage deformation of the cylinder head plane is greater than the specified value, the cylinder head can be placed on a special platform, and a pad iron with a thickness of about 4 times of the deformation can be padded between the two ends of the cylinder head plane and the flat plate, so that the middle of the cylinder head plane is suspended. Then press down the bolts, preheat the middle part of the cylinder head with a blowtorch to make the temperature reach 300-400 ℃, continue to press the pressure to make the middle part fit with the reference plane, knock the reinforcing rib of the cylinder head with a hammer for 2-3 times, stay for about 5 minutes, move the pressing plate to the two ends of the 1 / 3 of the total length of the cylinder head, and knock them respectively. After staying for a period of time, loosen the hold down device, take out the cylinder head and check the correction. If it does not meet the technical requirements, it can be combined with scraping to trim the plane. (2) Surface grinding method. Put the cylinder head face up on the support frame, tighten it after leveling, and grind it. (3) For the bulge near the bolt hole, it can be pushed by oilstone or fine grinding wheel or smoothed by fine file. (4) The cylinder liner is too much higher than the upper plane of the cylinder block, which is generally caused by improper selection of the cylinder liner or serious carbon deposition between the cylinder block and the step hole of the cylinder liner. It is necessary to replace the appropriate cylinder liner or clean up the carbon deposition. When the height of each cylinder liner higher than the upper plane of the cylinder block is inconsistent, copper pad should be added under the too low shoulder of the cylinder liner to make the height higher than the upper plane of the cylinder block consistent. During installation, pay attention to tighten the cylinder head bolts in 2-3 times according to the sequence of first middle and then diagonal.

2 cylinder gasket burned

Cylinder head gasket is an elastic gasket installed between the cylinder head and the engine body. Its function is to prevent air and water leakage of the engine. The cylinder gasket is in direct contact with high temperature, high pressure gas and coolant, so it is easy to be ablated in the use of tractor, especially around the edge of cylinder. When the cylinder gasket is ablated, there will be air leakage and water leakage at the bottom plane of the cylinder head; the engine will overheat and run weakly.

A diesel engine runs unsteadily, starts difficultly and the power drops obviously; when idling, the exhaust pipe has "sudden, sudden" sound; at the same time, the lubricating oil level in the oil pan rises, there are bubbles in the radiator, and there are water drops at the muffler port, which is a typical cylinder gasket burning failure. When checking the cause of the fault, it is found that there is no warpage or unevenness in the plane of cylinder head and cylinder block, the tightening torque of cylinder head bolts and nuts also meets the requirements, the installation direction is correct, the thickness of cylinder gasket is uniform, and the thickness also meets the requirements. Finally, it is found that the height of the boss of individual cylinder sleeve is not enough, which leads to the different height of each cylinder; and because the bolt holes of cylinder block are corroded after long-term use, the bolt holes become shallow, and the bolts can not be screwed to the bottom, so that the cylinder head can not compact the cylinder pad, causing the cylinder pad burning. During maintenance, the copper washer can be put under the step of the cylinder liner with too low boss height. After checking that the height of the cylinder liner boss is basically the same, it can be reassembled and the fault is eliminated.

After the cylinder head gasket is burnt out, attention should be paid to the selection of cylinder head gasket with good quality and matching with diesel engine specifications. In the case of no replacement of new cylinder gasket, the replaced old cylinder gasket can be roasted evenly with fire to make its internal material (asbestos) become a little loose, so that it can be installed after natural cooling. For the cylinder head gasket which can be installed on the opposite side and has curling edge, do not install it on the opposite side, and make the smooth side face up. If there are installation marks, they shall be installed in the direction of the marks. During installation, the bolts shall be tightened according to the specified torque, tightening times and sequence. After a period of use, the cylinder head bolts should be rechecked and tightened again. In addition, the screw hole debris should be cleaned regularly to ensure the seal between the cylinder head, cylinder gasket and cylinder block. In use, it is necessary to prevent the water shortage of the cooling system of the diesel engine from causing the working temperature to be too high, and avoid the long-time, low gear and overload driving of the vehicle.

3. The cylinder head is cracked

When the engine power is low, the oil in the exhaust tank is not stable, and the oil in the exhaust tank is not stable.

The causes of cylinder head cracks are as follows: first, improper use, such as forgetting to add water before starting or the water level in the water tank is too low, and suddenly adding cold water when the engine is working at high temperature. When the temperature is very low in winter, the cooling water is not drained or the cooling water is not drained after parking, which will make the cylinder head and cylinder body temperature change rapidly and produce cracks. The other is improper installation. When the cylinder liner is pressed into the cylinder block improperly, it is easy to cause cracks in the cylinder liner after a long time of work. The fillet of the protruding shoulder section on the upper part of the cylinder liner is too small or right angle, or the shoulder is too high, resulting in cracks in the cylinder liner or cylinder head due to stress concentration. The cylinder head gasket is not installed correctly or the cylinder head bolts are not tightened in the required sequence. Third, there are sand holes or cracks in the cylinder block or cylinder head.

Prevention and elimination methods: in use, it is forbidden to start the engine without cooling water. When the ambient temperature is lower than zero, the cooling water in the water tank and water jacket must be drained after the work is finished and the water temperature is reduced. For the forced cooling system, when the engine is overheated and the water tank is short of water, the engine should run at low speed, and then slowly add the cooling water after the water temperature is reduced; Soft water should be used and the scale in the water jacket of the cooling system should be removed regularly. If water enters the oil pan or is found in the exhaust, the cylinder head should be removed for inspection to find out the leakage and eliminate it. When the cylinder block or cylinder head has a slight crack, it can be sent to the repair shop for repair by welding or inorganic adhesive.