JAXAshby wrote:
If one has a hard time recognizing the sounds of pressure oil bearings working
without pressure oil to them, start your engine right off, listening to the
sounds coming out, taking care to hear the change in sounds over the next ten
to sixty seconds (much quieter), let the engine run a couple minutes and shut
off. Then restart and notice the difference in sounds.

Just remember that the pressure from the pump is only to supply oil to
the bearings (and maintain sufficient flow for cooling). The film the
journal "flys" on is extremely high pressure that is dynamically
generated by the spinning journal. Regardless of oil pressure from the
pump, there is metal-to-metal contact at start-up until the oil wedge
establishes itself.

All good things are on the web, and easier to find then my college notes:
http://www.roymech.co.uk/Useful_Tabl...ubrication.htm

I've never seen a hydrostaticly lubricated machine outside a lab (note a
total of four sentances in this discussion). For practical purposes,
only the hydrodynamic section is applicable; see the table in the link.
Note 1 MPa ~= 145 psi, so oil film pressure in most bearings we deal
with will run from 750 - 3000 psi. Obviously not pump pressure.

The oil must be there to develop the film, but the film thickness is
thousandths of an inch. There is going to be sufficient oil unless the
engine has been rebuilt or has been sitting a long, long time. The oil
pump maintains a flow of oil for cooling and replacement of displaced
oil. The start-up noises arise because it takes a finite period for the
oil wedge to develop.

dave

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