A BMW 320i car with a mileage of about 70 thousand km in 2004. User response: when the engine is overhauled, the engine will have abnormal noise when accelerating. After receiving the car: using fault detector ISTA to detect, do not find fault code; check some basic data of engine, are normal. Start the engine, step down the accelerator pedal, when the engine speed is 3000 r/min to 4000 r/min, the noise is very loud, and it can feel the steering wheel in strong vibration. The lift was lifted by the lift. It was found that the engine and the automatic transmission did not touch the car body, all the supports were normal, and the torque converter did not jump obviously. After repeated checks, it was found that the engine oil pan vibrated strongly when the engine speed reached 4000 r/min. Considering that the engine has been overhauled, it is decided to remove the oil pan and check whether the balance shaft assembly is normal. Remove the oil pan and check that the assembly position of the balancing shaft is exactly the opposite of the correct assembly position. Troubleshooting: after assembling the balance shaft again and correctly, the abnormal sound and vibration will disappear.