The cylinder head is one of the important parts of a diesel engine, mainly used to close the cylinder, but also is the installation base of many parts. The cylinder head is not only subjected to high temperature and high pressure of the gas, but also to the preload of the cylinder head bolts. In addition, the heat load of the cylinder head is very serious, and the temperature distribution of its bottom surface is extremely uneven. Deformation and cracks are common failures of the cylinder head. Understanding the causes of deformation and cracking, doing a good job of prevention, and mastering the diesel engine cylinder head deformation and cracking repair methods, to improve the performance of diesel engines is of great significance.
1 cylinder head common damage
1.1 Cylinder head cracks
Fault performance: cylinder head intake and exhaust valve seat and the cylinder head wall between a narrow place, the place in use is most likely to produce cracks. When the cylinder head has a slight crack, the exhaust pipe smoke. After the cracks gradually expand and increase, the air will be scattered to the water tank, forming bubbles. Cooling water seepage into the cylinder, so that the engine is not good to start, white smoke, the sound is not good, power down.
Failure causes and preventive measures:
(1) design strength is not enough.
(1) The cylinder gasket is not well installed between the cylinder head and the cylinder body. Due to the inaccurate location of the hole, it reduces the flow of cooling water, which affects the cooling effect and makes the machine temperature rise. Therefore, when installing the cylinder gasket, be sure to carefully check the alignment of the holes. The cylinder gasket with too much difference in hole position cannot be used.
.(3) in use when the machine temperature is high, the addition of cooling water. The sudden heat and cold caused cracks. Therefore, in the machine temperature is very high when not allowed to add cold water to the tank suddenly. In the operation method, it is strictly prohibited to start the engine first and then add cooling water.
(4) the oil supply time is too late for a long time so the engine overheats. Therefore, when the oil supply time is found to be abnormal, it should be adjusted.
(5) often use hard water. Because hard water is easy to generate at scale, coupled the cooling system is not cleaned in time so that the cooling system’s cooling capacity is reduced, easy to cause cylinder head cracks. So, must use soft water according to technical requirements, and timely cleaning of the cooling system.
(6) often use a decompression mechanism to stop. Parking with this operation method, so that the engine in the high temperature inhaled too much cold air, resulting in sudden cooling and cracking of the cylinder head. Therefore, in general, do not use the decompression mechanism to stop.
Cylinder head cracks inspection method: commonly used are observation method, fluorescence flaw detection method, hydraulic test and magnetic flaw detection method.
Crack repair: available welding or gluing repair. In addition, you can also use a comprehensive repair method and with pliers, welding, gluing and other processes to repair. Cylinder head repair after the hydraulic test, in 03 ~ 04 MPa of pressure, 3 min no leakage or seepage for qualified. Check the warpage of the plane shall not be greater than 015 mm. cylinder head plane warpage greater than 015 mm to be milled. Put the cylinder head on the plane milling machine, milling plane, eating tool depth 015 mm, once milled.
1.2 Warpage of cylinder head bottom plane
Warpage performance: cylinder block and cylinder head flatness error exceeds the limit, will cause the cylinder seal is not tight, water leakage, air leakage, resulting in compression force is not enough, in serious cases will wash bad cylinder gasket.
Warpage causes: when the diesel engine is working at high temperature, sudden cooling; during assembly, the cylinder head bolts are not tightened according to the specified order 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 disassembled in a hot state, it will cause the bottom plane of the cylinder head to warp and deform.
Check the flatness of the cylinder head and cylinder block contact plane: put the flat ruler on the cylinder head plane, use the thickness gauge to measure the maximum value of the gap is the flatness of the plane. Common models of engine cylinder head flatness technical requirements are: EQ6I00-I engine cylinder head in 100 mm length is not more than 0.03 mm, in the full length is not more than 0.10 mm; leap into the NJ130 requirements is not more than 0.10 mm, diesel engines generally require not more than 0.10 ~ 0.10 mm. generally speaking, the higher compression of the diesel engine cylinder head, longitudinal The cylinder head with shorter size has higher flatness requirements, and vice versa.
Repair method: (1) scraping and research method. Scraping before the cylinder head and inspection platform clean. In the inspection platform work surface, coated with a thin layer of red Dan oil or red seal oil, the cylinder cover is gently placed on the plane, so that the cylinder cover plane and the platform contact, and pushed back and forth grinding 3 ~ 5 turns, and finally remove the cylinder cover, view the plane warped protruding part (has shown the red Dan oil marks), and then scrape with a scraper scraping marks part, repeat several times until meeting the requirements. The quality of the scraping repair is generally checked according to the number of points evenly distributed on the work plane. As long as the print point size is basically the same, and uniform distribution, that is, the quality is considered good. (1) mutual research method. In the cylinder body and cylinder head coated with grinding paste, direct grinding is a method to eliminate warpage. Before grinding, use cotton yarn or grease to block the waterway and bolt holes on the two planes of the cylinder body and cylinder head to avoid falling into the abrasive. Then fix the cylinder body on the machine base or wooden frame, so that its plane is in a horizontal position. When grinding, first in the cylinder body plane thinly coated with a layer of abrasive (generally by the valve sand and oil blend). Then put the cylinder head flat on the cylinder body, so that the cylinder head plane and the cylinder body plane are against together, and then back and forth, left and right to push the cylinder head so that the two planes grind each other. After 10-10 min, take off the cylinder head, remove the old abrasive, apply the new abrasive and continue grinding until there is no obvious black trace on the plane of the cylinder body and cylinder head.
Go ahead If you would like to know more about the structural characteristics and assembly technology requirements of diesel engine cylinder head assembly