Crankshaft seal rings, also known as rear main seals, create a dynamic barrier against oil leakage between the crankshaft and engine block. Positioned at the rear of the crankshaft where it exits the engine, these seals prevent oil escaping from the engine’s oil pan. Typically constructed from nitrile rubber, silicone, or viton, designs include single-lip, dual-lip, and positively sealed variations to accommodate differing engine pressures and shaft speeds. Internal spring tension maintains consistent contact with the crankshaft surface, and materials are selected for resistance to petroleum products and elevated temperatures. Proper installation requires lubrication and precise alignment to ensure sealing effectiveness and prevent premature failure.