Valve thermal conductivity, corrosion resistance is high. When air-fuel mixture gas is burn in cylinder, it’s temperature is increased. Valve material should be use high thermal resistance which is not under the wrap influence the heat. Otherwise it will be leaked. Valve head and valve seat material should be hardness with high temperature. Without it can nod work accurately. In valve mechanism also should be used lubrication. Because rapidly open and close valve there have no corrosion. If any one want to good working efficiency they must be used speedy by using lubrication. If do not use lubrication, or small amount use which is not enough stems do not work. In outlet valve where gas burning much. And exhaust gas speed is up to three hundred fps. It create corrosion by air-fuel mixture. When working temperature is maximum that’s time valve may be broken or destroyed much which is short distance. It is generally occurred corrosion fatigue or i
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