JAXAshby wrote:
dave, nice explanation of how an oil pump would fail to provide any oil at all,
let alone pressure oil, to even the first bearing in line upon engine startup.

think of the grinding, clashing, rubbing, clattering you would hear on the
bearing for a minute or two or five.

Thus the old practice of chucking a rod with appropriate gear on the end
in a drill motor, pulling the distributor, and spinning up the oil pump
on older engines after a rebuild.

A bit out of my field, but I believe most of the noise I have
encountered with engines at startup (at least those that haven't been
sitting too long) is top end noise (vice more expensive bottom end
issues) and usually associated with hydraulic lifters pumping up vice
bearing issues. Recall that there is a fair amount of oil retention in
the bearings for extended periods of time, and the separation of the
journal from the bearing on oil during operation is based on pressure
developed by the rotating journal, not the oil pump. I believe the pump
sustains the quantity of oil and therefore only indirectly the thickness
of the oil wedge supporting the journal. My college machine design notes
and textbooks are in the basement and I don't really want to go dig them
out, but I believe my recollection is accurate.

dave

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gene, you klutz. Look what you said:

too viscous to be
pumped at low temperatures and the pump simply doesn't prime

and

an oil pump is not a suction pump...

so which is it, gene? an oil pump needs a prime, or an oil pump is not a
suction pump.

Or ...

.... you don't have a clew what the word "prime" means?

gene, have you any idea what kinds of bearins **require** pressure oil?

it seems not.

Thus the old practice of chucking a rod with appropriate gear on the end
in a drill motor, pulling the distributor, and spinning up the oil pump
on older engines after a rebuild.

yup.

and also the reason race car engines and race motorcyle engines are spun up
with the ignition off to achieve pressure oil to all the bearings needing
pressure oil before lighting the fire.

Also the reason aircraft owners who care about their engines run the prop
through a number of times before turning the mags

Also the reason the US Navy has prelube precedures for piston engines.

I believe most of the noise I have
encountered with engines at startup ... noise ... associated with hydraulic
lifters pumping up

you can hear that alright, but listen to the other clattering going on. It is
pretty serious noise.

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.

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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Jax,

I could not bear to dig through the rest of the thread to see if the
complete story got put together, so here it is....

If you had ever in your short life built up an engine, you would know
that priming the oil pump is an important consideration for a new engine
only. Most all of your little engine have the oil pump above the rest
oil level (shown by the full mark on the level indictaor stick).

Any worthwhile engine is designed so it will hold enough oil in the
sitting still pump to make it seal up on the next turn of the crank
shaft. This is not hard to do, but is is why small engine lube oil pick
up tubes often go into the pump body above the pumping element.

Any Positive Displacement pump that is nearly sealed can easily achieve
a suction side depression (negative pressure) in the 29"Hg region.

As most lube oil components vapor pressures are very low (small mm Hg @
300F), flashing the lube oil is not one of the things that design people
worry about at all.

As a lab rat (consulting, contract or direct) for several major
manufactures including some automotive over multiple decades, the "time
to lube" is a function addressed early in phase zero or phase one
developement of most engine programs. And, thirty seconds to have oil
on the valve gear is acceptable. Remember, this is an engine like most
of the rest of the world and it has about a pound of oil in it you can
never drain out (ask anyone that though he was breaking down a dry
engine).

The only engines that I recall immediately that had the lube oil pump in
the oil are the older BMW and some recent Mitsubishi. Those both had
chain drive oil pumps in the pan. Most everything else does not. Quite
a number of in-line engines have the lube oil pump mounted externally on
the the outside of the crankcase on the other end of the distributor drive.

Matt Colie Lifelong Waterman, Licnsed Mariner and Pathological Sailor
Engine Development and Durability Dynomometer Laboratory Supervisor
Engine Component Development Engineer Supervisor and
Participant in four "clean paper" engine programs also
Chief Engineer of Steam or Motor Vessels - Any Horsepower


JAXAshby wrote:

genee/rickie claim that oil pumps have to spin for some time to draw a prime.

I am trying to visualize how an oil pump draws a prime, particularly on oil at
say 15 degrees. In order to draw a prime the pump would have to evacuate the
air above the oil and below the pump, the difference in air pressure on the
evacuated side vs ambient air pressure leaves no more than a few pounds of
pressure total (can't be more than 14.7# total, for that is atmospheric
pressure). Then the oil would have to vaporize and then be drawn into the
pump, then to be compressed back to liquid to then be pumped to the bearings
needing pressure oil.

At even normal room temperature engine starts -- let alone cold weather engine
starts -- it would seem an oil pump requiring a prime to work might take
several minutes engine run time to begin to pump even small amounts of oil.
Anyone know how the engine designers allow for this and still make the engines
last more than a minute or so? Anyone know of which engine designs have oil
pumps that have to pull oil up before pressurizing it? How do they get the oil
volume on such oil pumps?