The difference in viscosity at different temperatures is the viscosity index (VI). A steel base material is overlaid with a babbitt material and bored to a circular diameter equal to the shaft diameter plus the desired clearance. This thickness is crucial to the separation of the rolling and sliding elements in a bearing. I'm sorry this topic has been beaten to death here in SM, but I didn't find the specific info linking the numbers of clearances and viscosity. The Oil Viscosity Index is a rating system applied to engine oil that indicates how much an oil viscosity changes over a wide temperature range. Ex .001 x 2.00 shaft dia. 4 Effect of oil viscosity on oil pressure distribution at 2000, 4000 and 8000 RPM The proper viscosity of oil must be selected to match the operating temperature of the bearing to insure the oil film layer functions as designed. Grease with extreme-pressure additives also extends bearing life when subject to higher forces. General rule of thumb for determining oil clearance is .001 of clearance for every inch of shaft dia. Engine bearing clearance; Oil viscosity; Engine operating temperature; Crank surface finish and geometrical alignments; Just remember that bearing size needs to be uniform. Viscosity grade is dependent upon bearing RPM (of shaft), oil temperature and load. Scallops are cut at the splitline to admit oil. It is important to keep clearances in mind. Returning to the original question about establishing the proper oil flow to a journal bearing, in this instance, the clearance was known. Bearing Lubrication: Oil vs. simplest bearing called a plain journal bearing will be examined. To get proper lubrication to those bearings requires a thin oil like 5W-30. A sleeve bearing's operating mode is described in terms of a bearing characteristic number. Use 5W-30. Engine Oil Viscosity and Bearing Wear: Field Test Results 922342 Two programs were conducted to study the relationships between engine oil rheology and crankshaft bearing wear. (in.) Obviously, the clearance will be much smaller than the journal diameter (D), so this value is multiplied by 1,000 to make calculations easier. ¡【For modified rating life】In addition to the above, the contamination level or contamination factor, lubricating oil kinematic viscosity… “If the oil viscosity is too high the oil will thicken as temperature decreases, increasing torque and lowering operating speed. It can be induced by several conditions including: o. light dynamic and preload forces, o. excessive bearing wear or clearance, o. a change in oil properties (primarily shear viscosity), The plain journal bearing, shown in Figure 1, is the most basic hydrodynamic journal bearing. Now consider the effect of tight clearances on the hydrodynamic parameters. The viscosity of oil also changes in a non-linear away with the temperature increase from the shearing oil. Oil viscosity is determined by bearing clearance and modern vehicles use .001-.002 inch clearance. ¡Input shaft rot. The value Viscosity for journal bearing can range between 20 – 1500 cSt (Lansdown, 2004). ... Nominal bearing clearance ratio 0.002 Number of grooves 2 one of the biggest deciders of oil viscosity in modern engines is variable cam control as a heavy weight oil … For clearances smaller and larger than the rule of thumb ,refer to the factors listed below: Factors for tighter oil clearances: Smaller journals; Lower viscosity oils; Surface finishes min 4 RA L - Bearing length, inches m - Clearance factor N - Rotation speed -RPM Q1 - Minimum oil flow for full film W - Steady load - to be supported, lb Z - Lubricant absolute viscosity, centipoise. 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