Valve troubleshooting method
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Guangxi Yuchai Machinery Co., Ltd., on the basis of analyzing the causes of valve and valve seat wear failure, proposed a valve seat repair method.
 　
Valve and valve seat is one of the key components that affect the reliability and safety of the engine. It is mainly used to start and stop the intake and exhaust passages during the operation of the engine, and control the entry of fuel mixture or air and the exhaust emission. . Valve and valve seat work environment is very harsh, in addition to withstand high temperature gas corrosion, but also to withstand the impact of explosion pressure in the cylinder, the main failure mode is wear. There are four types of wear failures for valve and valve seats, namely contact fatigue wear, high temperature corrosion wear, abrasive wear, and high temperature creep. The wear failure process follows the law of wear of general mechanical parts, creep and corrosion media at high temperatures. Accelerate in this process. Studies have shown that the role of various corrosive media in gasoline engines and diesel engines is not exactly the same.
　　
Valve and valve seat also have some abnormal wear factors, such as: a large amount of dust in the combustion chamber air; too much carbon in the combustion chamber; water in the combustion chamber leads to valve and valve seat corrosion. Failure of engine valve and valve seat wear causes lax intake and exhaust passages to close, resulting in engine leakage, reduced cylinder pressure, reduced power, and increased fuel consumption. In severe cases, engine exhaust fumes will also be emitted. Air filter Qi, starting difficulties and so on.
　　
Valve seats usually have two types: One is directly from the cylinder head. This type has a good heat dissipation performance, and processing is also more convenient; the other is to insert a valve seat on the cylinder head, this type is easy to repair and replace, cylinder head and valve seat with interference fit to ensure reliability.
　　
â—† Valve seat removal method
　　
Since the valve seat ring and the cylinder head are in interference fit and the inner bore surface is smooth, the valve seat must be removed to establish a stress point on the valve seat ring or to dismantle the valve seat ring in a destructive manner. There are usually several ways:
　　
1, cutting method
　　
That is, the valve seat is cut off with a tool on the machine tool. When the valve seat ring is thinned, the valve seat ring shrinks and loses the interference fit with the bottom hole of the valve seat ring. Under the action of the cutting force, the valve seat ring rotates together with the tool, which may result in the valve seat bottom hole. The size of the changes, roundness does not meet the technical requirements. Therefore, when this method is used to remove the valve seat ring, in order to ensure a good interference fit between the valve seat ring and the bottom hole of the valve seat ring, it is generally required to enlarge the size of the bottom hole of the valve seat ring with a tool, and at the same time, to increase the outer diameter size. Valve seat is used with it.
　　
2, drawing method
　　
That is, a drawing tool is used to pull the valve seat directly from the cylinder head. For example: first tap the thread on the inner surface of the valve seat ring, and then screw the corresponding size of the threaded rod into the valve seat ring. When the valve seat ring and the threaded rod are vertical, tap the threaded rod with a hammer. Until the valve seat is pulled out. The drawing method will basically change the size of the bottom hole of the valve seat, and the size change will depend on the drawing method of the drawing tool and its force mode.
　　
3, welding heating method
　　
That is to say, the welding device is used to heat the valve seat ring with a welding rod so as to achieve the purpose of breaking the interference fit between the valve seat ring and the bottom hole of the valve seat ring. The usual practice is to continuously and evenly spot welds along the inner surface of the valve seat ring with a welding rod. When the valve seat ring is heated and reddish, cold water is immediately poured onto the valve seat ring, and the valve seat ring usually breaks. It is not appropriate to use this method to heat the valve seat for a long time. Generally, the valve seat is heated until it turns red.
　　
4, induction heating method
　　
Induction heating is a method of heating metal materials by converting the power frequency power source into a specific frequency band using the principle of electromagnetic induction. Induction heating system consists of induction coil, AC power supply and workpiece. The alternating current in the induction coil causes the valve seat ring to generate eddy currents, thereby achieving the purpose of heating the valve seat ring. Tests have shown that the use of induction heating equipment on the valve seat heating 3-6s, the valve seat can be easily removed from the cylinder head, valve seat bottom hole size and surrounding metal microstructure without any change. It is also not suitable to use this method to heat the valve seat too long, otherwise it may change the metallographic structure of the cast iron around the bottom hole of the valve seat.