A Changan Ford Mondeo 2004 with a mileage of about 180 thousand km and a Duratec-HE 16 valve engine. The car was towed to my repair station for overhauling because it could not start. Inspection and analysis: after enquiring the customer, it was learnt that the engine noise was very heavy in the car, and a malfunction that could not be started recently. The engine has been repaired in a small repair factory a month ago because of the failure to start. The customer is not sure how to repair it. Only the engine can be started after the maintenance. First check that the oil and coolant are at the normal level, but there is metal powder in the oil. Viewed from the hood of the engine valve chamber to the engine, it was found that the inside was very dry, and there was no fresh oil. When the valve chamber was removed, it was found that the camshaft was broken because of the serious lack of lubricating oil. The engine oil pump was not found to be abnormal, so the engine cylinder was disassembled to check the oil channel. After removing the cylinder head, it is found that there is a foreign body in the main oil main way of the cylinder body. The foreign body taken out is a pile of cotton wool, just blocking the oil hole. Moreover, I found that the cylinder head was once dismantled, and there were many red sealants on the cylinder head. The maintenance work was very rough. Troubleshooting: because the engine cylinder head and camshaft were damaged badly, the customer had to replace the engine assembly. Maintenance summary: the breakdown of the vehicle is a typical man-made fault caused by barbarous maintenance. Before the maintenance personnel in the maintenance process in order to prevent the debris to drop the cylinder body of the oil channel, the use of cotton clogged the oil channel, later forgotten to take out, the result caused serious consequences. I borrow the case of the car to give my maintenance staff a lesson, as a maintenance personnel, in addition to a strong technology also have a strong sense of responsibility, in order to repair the car at the same time will not leave a fault.