How are engine valves lubricated?

The lubrication of engine valves is primarily achieved through two methods: splash lubrication and pressure lubrication. Splash lubrication relies on oil droplets splashed by the rotation of the crankshaft and camshaft or engine oil ejected from the oil holes in the connecting rod big end to coat components such as valve stems and valve guides. This method is structurally simple but depends on oil quality and oil level height. Pressure lubrication employs an oil pump to pressurize the lubricating oil, which is then delivered through dedicated oil passages to critical areas like the valve rocker arm shaft, forming a stable oil film suitable for high-load zones. Some designs incorporate oil holes in the valve guides to allow engine oil to seep into the clearance between the valve stem and the guide. During lubrication, the engine oil must possess excellent high-temperature oxidation resistance and detergency to prevent valve carbon buildup. It is recommended to regularly check the oil level and replace it with manufacturer-specified oil, such as API SN or SP grade full synthetic oil, while ensuring proper valve clearance adjustment, which is vital for maintaining lubrication effectiveness. For auxiliary components lubricated with grease, such as the throttle shaft, specialized grease should be replenished according to the maintenance manual schedule.