The oil seal is our first line of defense in regards to keeping lubrication inside the reducer. It might also be described as the last line of defense – keeping contaminants outside the reducer where they belong. The average seal is incredibly simple in design – made up of a case, a lip or lips, and frequently a garter spring. Of course, some are exponentially more intricate and are manufactured with unusual materials, but the majority are straightforward.

Operating temperatures for engine oil seals (see Fig. 14.1¹ and cross-section of lip seal with garter spring in Fig. 14.2²) vary widely, depending on engine design and location within the engine. Typically, the rear crankshaft seal is subjected to much higher temperatures than the front seal. Oil sump temperatures vary considerably, depending on provisions for oil cooling. This allows use of hydrogenated nitrile (HNBR), silicone, or acrylic elastomers for some seals in relatively low-temperature environments (120–140°C or 250–284°F). Standard fluoroelastomers (FKM), bisphenol-cured VDF/HFP/TFE terpolymers with 68–69% fluorine content, perform well in oil service up to about 160°C (320°F). More resistant fluoroelastomers are necessary for reliable long-term performance in more severe environments.