173C Sealed Valve

Also known as a toric joint — in reference to its torus shape — an O-ring is a gasket with a circular-looped design that’s used to seal two working surfaces. The valve stems in automotive engines, for example, often use O-rings to prevent oil from entering the combustion chamber. The O-ring creates a air- and liquid-tight mating surface between the valve stem and the valve guide. Without this small and otherwise simple component, oil may leak into the valve guide where it’s burned inside the combustion chamber.