Chevrolet Cruz 1.6L car with a mileage of about 89 thousand km. The car had an accident, the engine was repaired in other small repair shops, the customer reflected the engine fault light, and the test result was camshaft failure. Fault diagnosis: after maintenance, it is found that the camshaft signal gear is broken. After replacing the new camshaft, the test run is normal and delivered to the customer, but the customer still reflects that the engine still has abnormal sound. Related information: 2013 Chevrolet Coru (Cruze) original factory maintenance manual to test the car again, the car cool car sound normal, but after the hot car, there are "mouths clicking" sound. Normal vehicles also have "clatter" noises, but their voice is smaller compared with this vehicle. The engine has been disintegrated in other repair plants. Through dismantling, it is found that the key parts of the engine, such as pump, oil pump, camshaft sprocket, valve chamber cover and so on, have been replaced by auxiliary accessories. After changing the camshaft in my shop for the first time, we have explained to the customer that we only guarantee that your engine fault lamp camshaft fault is solved. In view of this situation, the customer agrees, except that the former camshaft noise is not ringing now. In view of this situation, I have provided two sets of solutions to customers. First, measure the oil pressure and check the valve clearance. Second, the engine is completely disassembled and repaired, replacing all the sub plant parts into original parts. The customer agrees to start with the first step: measuring the oil pressure and checking the valve clearance. The test results are as follows: intake valve one cold valve clearance 0.210 ~ 0.290mm, exhaust valve one cold valve clearance 0.260 ~ 0.340mm. The Cruz car adjusts the valve clearance through gaskets, and adopts different thickness gaskets for different heights. After dismantling the hot car, use the feeler to measure the clearance and find that the clearance is all larger than the normal value. At this time, the customer needs to replace all the gaskets, but the maintenance manual requires a cold measurement. For the sake of safety, we let the customer put the car in the store. After the engine is completely cooled, the clearance is measured again. All the results are within the standard range. At this point, we suggest that the customer take second sets of schemes: dismantling the engine and replacing the associated auxiliary parts. As a result of the cost problem, the customer requests that the cylinder head inspection be dismantled first. After the dismantling, the cylinder head was flat, and the valve chamber was filled with water. It was found that the seal was very good (the invention of the method of earth, but after this maintenance, I found this method is still unscientific). Look at the valve, no trace of the valve. When the valve was removed, no anomalies were observed. Since there is no special valve measuring device, we can only observe the valve. Careful observation shows that the valve and the valve port are a little tight. The contact surface between the normal valve and the air door should be very close, and it should be very loose with the external top valve, but the car's valve is fully combined with the gas gate, so it can be moved with greater force. At this time, the valve is slightly moved out of a small seam, so that there is a distance between the 0.5mm and the gas gate, with a plastic tube, the bottom of the valve, the valve, find the gas gate problems. During the dismantling process, it was found that there were many sealants in the camshaft sprocket oil way, and it was suspected that there was something wrong with the oil way check valve, so it was ready to be dismantled and replaced. I heard that the replacement process was particularly troublesome. I did not believe it at the time. As a result, two people in my factory had been dismantled for a whole afternoon. Figure 1 was a special tool made by me, hoping to give some inspiration and help to the colleagues. Replace all the valves. After loading, everything is normal and troubleshooting. Maintenance summary: in view of this vehicle's maintenance process, summarized two points. First, we should attach importance to communication skills with customers. In view of the vehicles that have been repaired in other repair plants, it is necessary to speak to the customers before maintenance, or to replace all the parts of the original plant for repairable, or only to guarantee the quality of the replacement parts. Otherwise, future problems may lead to misunderstanding. In addition, you can not blindly follow the customer's advice. Second, the ingenious use of special tools. There are no special tools for the repair of some components. Only by using reasonable tools and reasonable methods can we accomplish tasks faster and more efficiently. Failure review: after reading this case, speak frankly, until the end of the article did not see the true cause of the engine noise has a relatively clear diagnosis. Is it because the replacement of the pump, oil pump, camshaft timing sprocket, valve chamber cover and other key components of the engine accessories for the sub factory will produce this abnormal sound? And when the engine trouble lights are checked, the process of changing the camshaft can not be found in the presence of the engine, or some of the suspicions that produce the abnormal sound. So I think the maintenance technician in the diagnosis of engine fault lights, the replacement camshaft repair scheme is not comprehensive, so that the fault can not be repaired once. From the description of the failure phenomenon in the article, the author analyses that the true cause of the engine's abnormal noise may be that there are many sealants in the camshaft oil channel, which causes the inadequacy of the oil flow into the air distribution mechanism, resulting in the poor lubrication of the friction movement of the cam and the valve rod. This analysis is only for the author's reference. It is also hoped that the majority of readers will give comments on the fault diagnosis of the car two and the author's self-made special tools are worth affirming and encouraging, but the author should explain how to use the special tools in the article.