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Working Environment and Technical Condition of Engine Valve Guide
(1) Working environment of the valve guide: The valve guide is a guide for reciprocating movement of the valve, and the heat received by the valve head is transmitted to the conduit through the valve stem, and then transmitted to the cylinder head for heat dissipation. In addition to the temperature, the valve guide also receives the side pressure that the valve transmission transmits to the valve stem and acts on the valve guide through the valve stem. At the same time, there is no lubricating oil between the valve rod and the motion pair formed by the valve seat, which is dry friction, the friction is large, and the wear is large, so that the gap between the motion pairs is larger. Excessive matching clearance causes the valve movement to lose its guiding effect. When the valve reciprocates, the slanting of the valve makes the valve seat and the valve not sealed, thereby leaking gas, reducing power, increasing fuel consumption, poor emission and poor heat dissipation.
(2) Technical conditions of the valve guide: According to the working conditions of the valve guide, the material of the valve guide must be well-dissipated and wear-resistant. 1 catheter material: generally selected carbon steel, hardness 40 ~ 45HRC. 2 is arranged in a V shape with respect to the center line of the cylinder head. This arrangement can increase the water chamber in the middle of the cylinder head, enhance the cooling, and at the same time, the combustion chamber design can be more compact, the valve head diameter is increased, the exhaust gas is smoother, and the intake air is more sufficient. 3 The interference of the valve guide must be selected properly. Too small an interference will loosen the pipe and leak oil to the combustion chamber; too much interference will cause the cylinder head to burst when pressed into the pipe. The interference is generally chosen to be 0.027~0.045mm. 4 Press-in conduit: A. Heat the cylinder head evenly to 80 ° C ~ 100 ° C, and cool the valve guide to - 40 ° C. B. Quickly install the punch rod and press the tube into the tube hole on the cylinder head. When the upper end of the pipe is exposed to the inner surface of the basin-shaped groove of the cylinder head, it must be extended according to the specified value of the factory. Do not stretch too much, otherwise it will affect the valve spring work. When the length of the catheter is fixed, the upper end of the catheter protrudes too short, which means that the lower end of the catheter may protrude into the airway, which may affect the intake and exhaust. C. After the catheter is pressed, the inner hole is reamed according to the specification, and the roughness is Ral.6~0.8μm. The roughness cannot be high because the conduit and the valve fit clearance are not lubricated by the lubricant. In order to prevent the oil from leaking into the combustion chamber from the gap between the pilot hole and the valve, the valve oil seal should be installed at the upper end of the pipe.