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Malfunction: a Honda accord (equipped with F20A3 engine) went out in a long distance, and the engine was too hot to drive. The repair shop near it was overhauled. After the repair, there was a loud noise and slight jitter. After the vehicle was checked, it was found that the engine started cold start normally, accelerated well, idling slightly jitter, and exhaust emission was within normal range. Road test, speed up to 70km/h above, there is "GA, GA" abnormal sound, the sound is very light, but in the car can hear very clearly, and the engine has a slight jitter. The engine failure of the parking test is not obvious. Troubleshooting and Troubleshooting: the engine has just come out, and there is no such abnormal noise before. It can be concluded that the fault occurred after severe high temperature maintenance. There are several possible reasons for the noise: low octane number of gasoline; when ignition is not correct; the balance axis is not assembled at the right time; the geometric dimensions and gaps of each part are unsuitable and deviant. Start with gasoline according to the idea. Because the fuel tank in the tank is not much, add the 93# fuel, then check the ignition timing, and check the spark plug, then test the car, the noise is not removed, the jitter still exists. Next, look at the balance axis. Remove the balance shaft, drive the wheel housing, turn the crankshaft to the 1 cylinder piston at the upper stop point (TDC) position, check the balance axis and find that the rear balance axis is wrong. After adjusting with special tools, the balance shaft's field meets the requirements, and there is no jitter in the trial run, but the abnormal sound still exists. Only disassembly engine detection is needed to locate the root cause of the failure. Remove the engine from the car and disintegrate the engine. The piston, connecting rod, crankshaft, balance axis and other parts were tested, and the warpage of the cylinder head was measured as 0.07mm, and the error and improper sum were not checked. Since the problem was not detected, the engine assembly had to be carried out strictly in accordance with the requirements, in order to eliminate the failure of the previous overhaul, and the engine was carried on the test, and the noise was still not changed a little. Since all the parts data meet the requirements, why are there any abnormal noises? It seems that the fault must exist, but no investigation has been made, and the inspection is not detailed enough. Rearranging the train of thought, this vehicle caused the fault after severe heat, but there was no abnormal sound before. It seems that the sound is related to the high temperature. Now that the parts are all right, the problem is possible on the machine body that has not been found. Though this idea is a bit impulsive, it is possible to think it over carefully. The fault occurred after severe high temperature, and the engine of the car is made of aluminum alloy, which is prone to high temperature deformation. Only because the condition of this repair shop is limited, it is impossible to conduct scientific detection of the body. The only way is to replace the body. After discussing with the car owner, after cleaning and repairing an old body in the warehouse of the factory, the car body is replaced, the engine is tested, the engine is speeded up and the idle speed is smooth. The road test has no abnormal noise at all speeds, and the trouble can be eliminated. Who knows the car is back in two days. The driver said there was no sound, but the temperature of the vehicle was high. First, check the thermostat and cooling fan, run and open meet the requirements. There is only one possibility, that is, the high temperature and high pressure gas in the cylinder are interlinked with the cooling system, resulting in the increase of pressure and temperature in the cooling system. The cylinder head is removed, because the cylinder gasket is a steel cylinder cushion. There is no damage to the cylinder head. The warpage of the cylinder head plane is measured to be 0.15mm, which is beyond the scope of use. After the cylinder head was repaired with flat grinding, the high temperature failure disappeared. From the experience of the rework, it is no problem to measure the cylinder head after the first disintegration, but there is no measurement before changing the body. The disintegration of this assembly resulted in the warpage of the cylinder head. If the cylinder plane is measured before changing the body, the rework will not be done. At the same time, I hope your colleagues will pay attention to it, so as to cause unnecessary losses. Even after the demolition is finished, it is necessary to measure again.