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Old 06-19-2008, 06:26 PM   #15 (permalink)
ttoyoda
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Quote:
For aerodynamic air bearings this is certainly a true statement, but I do not know that it is a primary concern for plain bearings with sufficient oil pressure. Pressure in a fluid is applied evenly, more or less, to the surfaces.
There exist two types of air bearings: ones that do and ones that do not require an air supply. This second type lifts off when you spin it.
The oil pressure does not lift the crankshaft off the bearing shell. Oil pressure (or more accurately, flow) is needed to replace oil that leaks out the sides of the bearing shell and drips back into the oil pan.

Quote:
Also I can guarantee that for a given torque level, there are a lot greater forces at work and stress at higher rpms.
Yes. And the higher rpms also cause and increase the strength of the hydroplaning (hydrodynamic) effect of the crankshaft riding up on the oil film. So the bearing is protected.

Quote:
Pressure in a fluid is applied evenly, more or less, to the surfaces.
That is not true or relevant here. The oil is introduced into each bearing shell thru only one hole. A car engine is not a hydrostatic lubrication system, it is a hydrodynamic lubrication system. A system where fluid pressure was applied evenly all around the bearing would have a net sum force of zero, and would support nothing. You might as well drop the shaft into a pond of oil and watch it sink for all the support it would get. But it would have even fluid pressure around it, more or less, as it sank.

More info here:
http://www.bearingsindustry.com/aboutbearing/jb.htm

landspeed,
I am glad it worked out for you. Of course your results may not be reproducible for everyone else
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