Clevite Main BearingsMain Bearing SetVarious forms of main bearing grooving have been used over theyears. We are frequently asked what difference grooving makes.First, its essential to understand that bearings depend on afilm of oil to keep them separated from the shaft surface. This oilfilm is developed by shaft rotation. as the shaft rotates it pullsoil into the loaded area of the bearing and rides up on this filmmuch like a tire hydroplaning on wet pavement. Grooving in abearing acts like tread in a tire to break up the oil film. Whileyou want your tires to grip the road, you dont want your bearingsto grip the shaft.The primary reason for having any grooving in a main bearing isto provide oil to the connecting rods. Without rod bearings tofeed, a simple oil hole would be sufficient to lubricate a mainbearing. Many early engines used full grooved bearings and someeven used multiple grooves. As engine and bearing technologydeveloped, bearing grooving was removed from modern lower mainbearings. The result is in a thicker film of oil for the shaft toride on. This provides a greater safety margin and improved bearinglife. Upper main shells, which see lower loads than the lowers,have retained a groove to supply theconnecting rods with oil.In an effort to develop the best possible main bearing designsfor performance engines, weve investigated the effects of mainbearing grooving on bearing performance. The graphs on the nextpage illustrate that a simple 180 groove in the upper main shellis still the best overall design.While a slightly shorter groove of 140 provides a marginalgain, most of the benefit is to the upper shell, which doesnt needimprovement. On the other hand, extending the groove into the lowerhalf, even as little as 20 at each parting line (220 in total),takes away from upper bearing performance without providing anybenefit to the lower half. Its also interesting to note that asgroove length increases so do horsepower loss and Peak Oil FilmPressure which i