Clevite P-Series rod & main bearings are the oldest members of the Clevite 77 bearing family, and are intended for high-revving engines. To compensate for the high load factors and distortion in these engines, they have higher eccentricity and a high crush factor. P-Series bearings are built on steel backings with extra-thin overlays, to prevent overlay fatigue. In addition, the oil grooves on most applications extend all the way around both halves for better oiling. Complete set of Standard Size Rod Bearings, Main bearings, and Thrust washer.
Various forms of main bearing grooving have been used over the years. We are frequently asked what difference grooving makes.
First, it’s essential to understand that bearings depend on a film of oil to keep them separated from the shaft surface. This oil film is developed by shaft rotation. as the shaft rotates it pulls oil into the loaded area of the bearing and rides up on this film much like a tire hydroplaning on wet pavement. Grooving in a bearing acts like tread in a tire to break up the oil film. While you want your tires to grip the road, you don’t want your bearings to grip the shaft.
The primary reason for having any grooving in a main bearing is to provide oil to the connecting rods. Without rod bearings to feed, a simple oil hole would be sufficient to lubricate a main bearing. Many early engines used full grooved bearings and some even used multiple grooves. As engine and bearing technology developed, bearing grooving was removed from modern lower main bearings. The result is in a thicker film of oil for the shaft to ride on. This provides a greater safety margin and improved bearing life. Upper main shells, which see lower loads than the lowers, have retained a groove to supply the
connecting rods with oil.
In an effort to develop the best possible main bearing designs for performance engines, we’ve investigated the effects of main bearing grooving on bearing performance. The graphs on the next page illustrate that a simple 180° groove in the upper main shell is still the best overall design.
While a slightly shorter groove of 140° provides a marginal gain, most of the benefit is to the upper shell, which doesn’t need improvement. On the other hand, extending the groove into the lower half, even as little as 20° at each parting line (220° in total), takes away from upper bearing performance without providing any benefit to the lower half. It’s also interesting to note that as groove length increases so do horsepower loss and Peak Oil Film Pressure which is transmitted directly to the bearing.
These are not to be confused with the standard passenger car and light truck parts for the same retention applications which also have a “P” suffix letter. These high performance parts have unique core part numbers different from the standard parts for the same application. P-Series parts are the oldest series of Clevite high performance bearings. The rod bearings in this series typically have the greatest amount of eccentricity. Most rod bearings are available either with or without dowel holes for use in aluminum rods. Most P-Series main sets are full grooved to maximize oil flow to the rod bearings. Both rods and mains have high crush for maximum retention, and a reduced overlay thickness to prevent overlay fatigue, sometimes referred to as hen tracking.
Rod bearings use a hardened steel back for added strength and resistance to fretting. Extra clearance rod bearings are available for .001” additional clearance and select fitting. Use the P-Series rods where extremely high RPM’s cause severe rod bore close-in. This is typically indicated by nearly full parting line to parting line shaft contact with bearings having less eccentricity. Use P-Series mains where higher eccentricity is desired to narrow bearing contact patterns and to provide increased oiling to rod earings. Rod bearing oil starvation is typically indicated by polishing and smearing of the bearing surface, possibly accompanied by discoloration predominantly concentrated at the axial center of the bearings.