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It was presented in the previous paper (1) that oil leakage from valve stem seal (VSS) can be controlled by design and the characteristics of the newly designed composite VSS with a filled polyetrafluoroethylene (PTFE) layer lip are: a constant lower limit of oil leakage, minimal loss of power at low speed due to low friction, extended life over 300,000 km of vehicle traveled distance. It was also reported that oil leakage for lubrication can be determined by the stress distribution across the seal lip contact width touching the valve stem under a certain interference. However, the variable pressure inside Intake and Exhaust ports of an engine will affect the stress distribution of the seal lip causing the change in oil leakage. This report presents the design evaluation method and results of the improved VSS with filled PTFE layer lip which keeps the oil leakage constant even though the inside pressure of the engine port changes.

An internal combustion engine valve stem seal is actually a precision lubricating device that allows enough lubrication to the valve stem for extended life, but limits the lubrication to provide compliance with exhaust regulations, limits valve deposits, and prevents uneconomical oil consumption. The oil leakage for lubrication can be determined using four seal lip design factors. The long term stability of the oil leakage is provided by selecting polytetrafluoroethylene (PTFE) and fluoroelastomer (FKM) rubber as the seal materials, which are bonded together during vulcanization. The PTFE provides a low friction. low wear surface, and the FKM rubber provides a stable resilient body. Validation of the design factors is accomplished by precise measurement of oil leakage using actual engine components. After long term engine testing in the laboratory or field, the leakage can be re-measured. The leakage can be expected to increase only slightly.