Wanche. com expert Zeng Jian
Engaged in automobile maintenance for many years, with rich theoretical knowledge and practical maintenance experience. He also has a deep understanding of vehicle insurance, loss claims and vehicle service procedures.
case
Recently, Toyota Motor (China) Investment Co., Ltd. submitted a recall report to the General Administration of Quality Supervision, Inspection and Quarantine, and recalled some imported Lexus)LS series vehicles from July 19, 2010. According to statistics, there are 5,791 vehicles involved in Chinese mainland.
The reason for the defect is that the strength of the spring is reduced due to the tiny foreign matter mixed in the material of the intake and exhaust valves of the engine, which may cause damage. In this case, the engine will produce abnormal noise and cause poor work. In the worst case, the engine may stop working while driving, which is a potential safety hazard.
Expert diagnosis
The function of the valve spring mainly includes the following aspects: (1) to ensure that the intake and exhaust valves automatically return to close and seal; (2) Ensure the seating pressure between the valve and the valve seat; (3) Absorb the inertia force generated by the transmission parts during the opening and closing of the valve, so as to prevent various transmission parts from separating from each other and damage the normal operation of the valve train.
The fatigue life of valve spring mainly depends on working stress, material strength, surface quality, internal quality and manufacturing quality. Automobile valve spring belongs to cylindrical compression coil spring. Under the action of axial force, the shear stress on any cross section of the spring is the largest in the inner diameter of the spring and the smallest in the outer diameter. Therefore, the source of fracture failure and crack caused by design and material strength is often inside the spring.
Because the valve spring has been under the action of alternating stress, if there is a quality problem, the valve spring will have abnormal sound at first, and the acceleration performance of the car will decrease in serious cases, accompanied by difficulties in starting and poor working of individual cylinders.
When the valve spring breaks, the noise of the engine will increase, and in serious cases, the valve will not fully return, which will cause the piston to collide with the intake and exhaust valves, bend the valve stem, damage the piston, and even cause the cylinder head or cylinder block to be scrapped. At the same time, the engine will suddenly shut down, which will easily lead to serious traffic accidents.
Expert reminder
How to diagnose valve spring fracture? Whether the valve spring is broken can be seen by disassembling the valve chamber cover. When the engine speed changes, the valve spring will make obvious irregular noise; In static state, you can pry the spring with tools to check it, or you can slide the spring with tools. If the sound is different from other springs and hoarse, it means that the spring is cracked or broken and should be replaced in time.
What should I do when I find that the valve spring is broken? If several springs break at the same time on the way, which has affected the normal running of the vehicle, the driver must stop the engine in time. If there are no accessories or you can’t contact the 4S shop for the time being, you can find a professional maintenance person to remove the broken spring, face the flat parts at both ends, and then install it on the valve stem in the original way. This can temporarily ensure the normal operation of the engine, but the valve spring must be replaced in time after arriving at the 4S shop or the place where the 4S shop can be contacted.
Tips
valve spring
The valve spring is a cylindrical spiral spring and belongs to the valve train of the engine. The function of the valve train is to open and close the intake and exhaust valves regularly according to the needs of the working process of each cylinder of the engine, so that the fresh combustible mixture can enter the cylinder in time and the exhaust gas can be discharged from the cylinder in time.