Inliners International Forums General Discussion Hi Performance Forged pistons from LS1 in 292

This thread as diverged into two discussions.

Panic, concerning journal bearing oil flow and shaft support:
The shaft is lifted off the bearing surface and support by the oil wedge. This higher pressure film of oil is determined by the physical dimensions of the bearing, the bearing surface speed (affected by engine rpm), and actual oil viscosity (as affected by temperature).

Total journal bearing oil flow, for technical discussion, is divided into hydrodynamic flow (generally 80 to 85%) and pressure flow, sometimes also called side flow(generally 15 to 20%).

For a given journal bearing the hydrodynamic flow is basically caused bt the "pumping" action of the shaft/journal assembly, and is directly proportional to engine rpm.

The pressure flow is basically the additional oil flow to enhance cooling of the bearing, and is directly proportional to supply oil pressure.

A properly design journal bearing will operate with a flooded oil inlet at very low pressure, just several psi. The oil wedge will form a much higher local pressure to support the rotating shaft. Please note that a high pressure may be required at the beginning of an oil header/gallery to provided sufficent flow/pressure at the tail end of the header/gallery.

Unlike most flow/pressure relationships related to the velocity squared, these are directly proportional relationships.

On heavy rotating equiment, in some applications a secondary high pressure lifting oil or jacking oil is supplied to the bottom of the shaft or thrust bearing to phyically lift the shaft at start-up or low rpm's.

One source that discusses and gives calculations for journal bearing oil flow is the "Machinery's Handbook" in the 'journal bearings' section.