When the cylinder head is not sealed tightly, it will cause air leakage in the cylinder, resulting in insufficient compression pressure in the cylinder, a decrease in temperature and a reduction in air quality. When there is severe air leakage in the cylinder, the engine power will drop significantly, and it may even fail to work. Therefore, if a power drop fault occurs during the operation of the engine, in addition to finding the relevant fault causes that affect the power drop of the engine, it is also necessary to check whether the sealing performance of the cylinder head is good. Below, the author will analyze the main reasons that affect the sealing performance of engine cylinder heads for your reference.

1. The use and installation of the cylinder gasket are incorrect

The cylinder gasket is installed between the engine cylinder block and the cylinder head. Its function is to ensure the sealing of the combustion chamber and prevent the leakage of gas, cooling water and lubricating oil. Therefore, if the use and installation of the cylinder gasket do not meet the requirements, it will directly affect the sealing reliability of the cylinder head and the service life of the cylinder gasket.

To ensure the sealing quality, the selected cylinder gasket must be of the same specification and thickness as the original cylinder. The surface should be flat, the edge should fit firmly, and there should be no scratches, depressions, wrinkles or rust stains. Otherwise, it will affect the sealing quality of the cylinder head.

2 The slight jumping of the cylinder head

The slight runout of the cylinder head is the result of the cylinder head attempting to separate from the cylinder block under the action of compression and combustion pressure. These pressures elongate the connecting bolts of the cylinder head, thus causing a slight jump between the cylinder head and the cylinder block. This slight jump will cause the cylinder head gasket to undergo a process of relaxation and compression, thereby accelerating the damage of the cylinder head gasket and affecting its sealing performance.

3. The connecting bolts of the cylinder head have not reached the specified torque value

If the connecting bolts of the cylinder head are not tightened to the specified torque value, the wear of the cylinder gasket caused by this slight runout will occur more quickly and severely. If the connecting bolts are too loose, it will cause an increase in the runout between the cylinder head and the cylinder block. If the connecting bolts are tightened too much, it will cause the force on the connecting bolts to exceed their yield strength limit, resulting in the elongation of the connecting bolts exceeding their design tolerance limit. This will also increase the runout of the cylinder head and accelerate the wear of the cylinder head gasket. By using the correct torque specified value and tightening the connecting bolts in the correct sequence, the runout of the cylinder head relative to the cylinder block can be minimized, thereby ensuring the sealing quality of the cylinder head.

4. The plane of the cylinder head or cylinder block is too large

Warping and distortion are common problems with cylinder heads and are also the main reasons for the frequent burning of cylinder gaskets. Especially, the aluminum alloy cylinder head stands out more prominently. This is because the aluminum alloy material has a very high heat conduction efficiency. At the same time, compared with the cylinder block, the cylinder head is relatively small and thin, and the temperature of the aluminum alloy cylinder head rises quickly. When the cylinder head deforms, its connection with the cylinder block plane will not be tight, the sealing quality of the cylinder will decline, causing air leakage and burning out the cylinder gasket, which further deteriorates the sealing quality of the cylinder. If the cylinder head shows severe warping and deformation, it must be replaced.

5. The surface of the cylinder is not cooled evenly

Uneven cooling on the surface of the cylinder can form local hotspots. Local hotspots can cause excessive expansion of the metal in small areas of the cylinder head or cylinder block. This expansion can squeeze and damage the cylinder head gasket. Leakage and corrosion occurred due to the damage of the cylinder gasket, and it was eventually burned through.

If the cylinder gasket is replaced before the cause of the local hot spot is found, it will be of no avail, because the replaced cylinder gasket will eventually be burned out. Local hotspots can also cause additional internal stress in the cylinder head itself, resulting in cracks in the cylinder head. If the working temperature exceeds the normal temperature, local hotspots will also have serious negative impacts. Any overheating situation will cause permanent distortion and deformation of the cast iron parts of the cylinder block.

6. Issues related to additives in the coolant

When coolant is added to the coolant, bubbles may form. Bubbles in the cooling system can cause the cylinder head gasket to fail. When there are bubbles in the cooling system, the coolant cannot circulate normally in the system. As a result, the engine cannot be cooled evenly, and local hotspots will occur, causing damage to the cylinder gasket and leading to poor sealing. Therefore, in order to achieve uniform cooling of the engine, when adding coolant, the air must be expelled from the engine.

Some operators use antifreeze in winter and switch to water in summer, thinking it is more economical. In fact, doing so will cause endless troubles. The minerals in the water are prone to form scale and stick to the water jacket, radiator and water temperature sensor, causing inaccurate temperature control of the engine and leading to overheating. It may even cause faults such as damage to the engine cylinder gasket, warping and deformation of the cylinder head, cylinder pulling and bearing burning. Therefore, antifreeze should also be used in summer.

7. Poor maintenance and assembly quality of diesel engines

Poor maintenance and assembly quality of the engine is the main cause of the poor sealing quality of the engine cylinder head and also the main factor leading to the burning of the cylinder gasket. Therefore, when repairing the engine, it is necessary to strictly follow the relevant requirements and correctly disassemble and assemble the cylinder head.

When disassembling and assembling the cylinder head, it should be done when the machine is cold. It is strictly forbidden to disassemble it when the machine is hot to prevent the cylinder head from warping and deforming. When disassembling, it should be gradually loosened in several symmetrical steps from both sides to the middle. When the cylinder head and the cylinder block are firmly combined and difficult to remove, it is strictly forbidden to strike them with metal objects or insert sharp and hard objects into the gap to pry them open (an effective method is to use a starter to drive the crankshaft to rotate or rotate the crankshaft, and rely on the high-pressure gas generated in the cylinder to push them apart), to prevent scratching the joint surface between the cylinder block and the cylinder head or damaging the cylinder gasket.

When assembling the cylinder head, it is necessary to first remove oil stains, carbon particles, rust and other impurities from the mating surface between the cylinder head and the cylinder as well as the bolt holes in the cylinder block, and then blow them clean with high-pressure gas. To avoid insufficient clamping force of the bolts on the cylinder head. When tightening the cylinder head bolts, they should be tightened symmetrically from the middle to both sides in 3 to 4 steps. The last step should reach the specified torque, and the error should not exceed 2%. For cast iron cylinder heads, after the hot machine temperature reaches 80℃, the connecting bolts should be retightened according to the specified torque. For bimetallic material engines, such a retightening operation should be carried out only after the engine has cooled down.

8. Using inappropriate fuel

Due to different structural types of diesel engines, there are different requirements for the cetane number of diesel. If the selected fuel does not meet the requirements, it will not only lead to a decline in economy and power performance, but also cause a large amount of carbon deposits or abnormal combustion in the diesel engine, resulting in excessively high local temperatures of the engine block, causing erosion of the cylinder gasket and engine block, and reducing the sealing performance of the cylinder head. Therefore, the selection of cetane number for diesel in diesel engines must comply with the requirements of the usage regulations.

9. Improper use of diesel engines

Some engine operators, fearing that the engine might stall, always continuously slam on the accelerator when starting the engine or let the engine run at high speed as soon as it starts, in order to maintain the engine's working condition. During driving, the vehicle often shifts gears, stalls and coastes, and then shifts gears to force the engine to start. Under such circumstances, the engine not only increases the wear of the engine but also causes the pressure inside the cylinder to rise sharply, which is very likely to damage the cylinder gasket and lead to a decline in sealing performance. In addition, when the engine is often overloaded (or ignited too early), prolonged knocking and combustion can cause local pressure and temperature in the cylinder to be too high. At this time, the cylinder gasket is also damaged, reducing its sealing performance.

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