Main Bearings Depend on Good Oil Film
All bearings depend on a film of oil to provide support for the journals, and as we all know, the crankshaft should never actually come into contact with the bearing surface. The oil film is developed as the crankshaft rotates and oil is pulled into the loaded area of the bearing, allowing the journal to "ride" on this film similar to the way a tire rides on a film of water when it hydroplanes. Many early engines used full-grooved main bearings (a groove in both upper and lower shells) and some even used multiple grooves. As engine and bearing technology advanced, bearing grooves were removed from most modern lower main bearings. The result is a thicker film of oil for the crankshaft to ride on. This provides improved bearing life.
For performance applications,...
For performance applications, bearings with a "half-groove" are normally used. These bearings can also be a benefit in street-driven engines, as they provide better oiling than a bearing with just an oiling hole. The bearing's oil groove is only utilized on the upper half of the bearing, as the bottom half takes the most abuse from the upward force of the crankshaft, and, therefore, the lower half needs as much material as possible.
In order to develop the best possible main bearing designs for high-performance engines, Clevite has invested a considerable amount of time and research into studying the effects of main bearing grooving. This research has shown that the best overall design for Mopars and most other engines is one that features a simple 180-degree groove in the upper main bearing shells.
Selecting The Right Bearings
Clevite77 offers a line of bearings called TriArmor coated engine bearings. They feature a proprietary moly/graphite treatment applied to rod and main bearings. TriArmor provides extra insurance in severe use without compromising any existing bearing characteristics. These engine bearings are treated with a patented blend of molybdenum disulfide and graphite. Engine builders have long known that even modest reductions in friction can lead to measurable increases in power, and coated bearings deliver that.
The H-series is a popular design, suitable for a wide variety of high-performance and racing engines. In a nutshell, if you're unsure about which type of performance bearing to use, the H-series is an excellent candidate. These bearings were developed specifically for use in NASCAR-type applications, but are suitable for all types of competition and high-performance engines.
H-series rod and main bearings provide maximum crush and a medium level of eccentricity with a hardened steel back. Rod bearings also have a thin overlay. One very notable feature of the H-series bearings is a narrowed width to provide greater crankshaft fillet clearance. If your crankshaft features large fillets (common with high-performance crankshafts), and if the engine will run in the medium- to high-rpm range, the H-series is an outstanding choice.
The V-series rod bearings typically feature a low to medium eccentricity and provides a hardened steel back. For applications involving crankshafts with large fillets, narrowed bearings are available (under a VN suffix) to accommodate increased crankshaft fillet clearance. The primary difference between the V-series and other Clevite 77 TriMetal bearings is the use of a lead-indium overlay. A lead indium overlay offers a slightly better conformability than a lead/tin/copper overlay, along with slightly reduced wear resistance.
Fitting The Bearings
Since bearing thickness is greatest at the top center and bottom center (90 degrees from the parting line), always measure a bearing at 90 degrees to the parting line, in order to determine what your minimum oil clearance will be. When measuring bearing wall thickness, use a micrometer that features a ball-shaped anvil (use of a flat-anvil mic will result in an inaccurate reading).
A good way to measure bearing clearance is to measure the bearing inner diameter with the upper and lower bearing shells installed in their bores, and with the cap bolts fully tightened to the specified torque value. Once the bearings are installed and the cap is fully tightened, measure the installed bearing ID with a dial bore gauge.