Solve the problem of sealing performance of the cylinder

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The sealing performance of the cylinder head has a great impact on the technical condition of the engine. If the cylinder head seal is not tight, the cylinder will leak air, which will cause insufficient compression pressure of the cylinder, decrease in temperature and decrease in air quality. In severe cases, the engine power would be significantly reduced, and eventually, it cannot work. Therefore, if a power drop fault occurs during engine operation, in addition to finding the cause of the failure that affects the engine power drop, it is also necessary to check whether the cylinder head sealing performance is good. So, what are the main reasons that affect the sealing performance of the engine cylinder head?

1. Improper use and installation of the cylinder head

The cylinder gasket is installed between the engine cylinder block and the cylinder head. Its role is to ensure the sealing of the combustion chamber and prevent gas, cooling water and lubricant from leaking. Therefore, the use and installation of the cylinder gasket are not right, which directly affects the sealing reliability of the cylinder head and the service life of the cylinder gasket.

In order to ensure the quality of the seal, the selected cylinder gasket must have the same specifications and thickness as the original cylinder. The surface should be flat, the edges should be firmly bonded, and there should be no scratches, dents, wrinkles, and rust. Otherwise, it will affect the seal quality of the cylinder head.

2. Slight bounce of the cylinder head

The slight bounce of the cylinder head is the result of the cylinder head trying to separate from the cylinder block under the influence of compression and combustion pressure. These pressures lengthen the cylinder head connecting bolts, which results in a slight jump of the cylinder head relative to the cylinder block. This slight beating will cause the cylinder head gasket to relax and compress, thereby speeding up the damage to the cylinder head gasket and affecting its sealing performance.

3. The cylinder head connecting bolts do not reach the specified torque value

If the cylinder head connection bolts are not tightened to the specified torque value, the cylinder gasket wear caused by this slight runout will occur faster and more severely. If the connecting bolt is too loose, the amount of runout of the cylinder head relative to the cylinder block will increase. If the connecting bolt is over-tightened, it will cause the stress of the connecting bolt to exceed its yield strength limit, which will cause the extension of the connecting bolt to exceed its design tolerance value, which will also increase the amount of runout of the cylinder head. , Accelerate the wear of the cylinder head gasket. By using the correct torque specification and tightening the connecting bolts in the correct order, the runout of the cylinder head relative to the cylinder block can be minimized, thereby ensuring the seal quality of the cylinder head.

4, the cylinder head or cylinder plane is too large

Warpage and distortion are common problems in cylinder heads, and they are also the main cause of repeated burning of cylinder head gaskets. In particular, aluminum-alloy cylinder heads are more prominent. This is because aluminum alloy materials have high heat transfer efficiency. At the same time, the cylinder heads are smaller and thinner than the cylinder block. The temperature of aluminum alloy cylinder heads rises rapidly. When the cylinder head is deformed, it will not be tightly connected with the plane of the cylinder block, and the sealing quality of the cylinder will be reduced, resulting in air leakage and burning of the cylinder gasket, thereby further deteriorating the sealing quality of the cylinder. If the cylinder head is severely warped, it must be replaced.

5, uneven cooling of the cylinder surface

Non-uniform cooling of the cylinder surface will form local hot spots. Local hot spots can cause excessive expansion of the metal in the cylinder head or a small area on the cylinder block, which can squeeze and damage the cylinder head gasket. Leakage and corrosion caused by the damage of the cylinder gasket, and eventually burned through.

If the cylinder head is replaced before the cause of the local hot spot is found, it will not help, because the replaced cylinder head will eventually burn out. Local hot spots also cause additional internal stress on the cylinder head itself, which results in cracks in the cylinder head. If the operating temperature exceeds the normal temperature, local hot spots will also have serious negative effects. Any overheating will cause permanent distortion of the cast iron parts of the cylinder block.

6. Problems related to additives in the coolant

When the coolant is added to the coolant, bubbles may be generated. Air bubbles in the cooling system can cause cylinder head gaskets to fail. When there are bubbles in the cooling system, the coolant cannot be circulated normally in the system, so the engine cannot be cooled uniformly, local hot spots will occur, and the cylinder gasket will be damaged, resulting in poor sealing. Therefore, in order to achieve uniform cooling of the engine, air must be discharged from the engine when the coolant is added.

Some robots use antifreeze in winter and switch to water in summer, which is considered economical. In fact, there are endless problems because the minerals in the water are prone to scale and stick to the water jacket, radiator, and water temperature sensor, which will cause the engine temperature control to be inaccurate and cause overheating. , Pull cylinder and tile burning failure. Therefore, antifreeze should also be used in summer.

7. Poor quality of diesel engine maintenance and assembly

The poor quality of engine maintenance and assembly is the main cause of the seal quality of the engine cylinder head, and also the main factor that causes the cylinder gasket to burn out. For this reason, when repairing the engine, we must strictly follow the relevant requirements and properly disassemble and assemble the cylinder head.

When disassembling and disassembling the cylinder head, it should be performed in a cold state, and it is strictly prohibited to disassemble in a hot state to prevent the cylinder head from warping and deforming. When disassembling, loosen gradually from the two sides to the middle symmetrically. If the combination of the cylinder head and the cylinder block is difficult to remove, it is strictly forbidden to strike with metal objects or use hard and sharp objects to embed hard cracks in the seam. High-pressure gas) to prevent scratching the joint between the cylinder block and the cylinder head or damage the cylinder head gasket.

When assembling the cylinder head, first remove the oil, carbon particles, rust and other impurities in the joint surface of the cylinder head and the cylinder, and in the bolt holes of the cylinder block, and blow it off with high-pressure gas. In order to avoid insufficient pressure on the cylinder head by bolts. When tightening the cylinder head bolts, it should be tightened symmetrically from the middle to the sides 3 to 4 times. The last time to achieve the specified torque and the error is ≯2%. Re-tighten the connecting bolts with the specified torque. For bimetallic engines, such a re-tightening operation should be performed after the engine has cooled.