At rest there is metal-to-metal contact.
That contact continues until oil pressure can hydraulically
separate the components.
Hence the premise: "highest wear at start-up".
The thin film that "clings" is insufficient to protect
against this wear.
I guess my question would be that if you do not think oil pressure is important then why not drain the oil from the engine and drive it?
Because that is where the vast majority of lubrication comes from.
I guess my question would be that if you do not think oil pressure is important then why not drain the oil from the engine and drive it?
My point exactly. The engine doesn't lay in oil, it requires oil pressure to lubricate it.
It does not, it only requires a film of oil to be present and that the rotating units in question do not overheat.
Lots of engines have hydro-dynamically lubricated bearings.... without a pressurized oiling system.
A pressurized oil system based engine requires pressurized only in that it has no alternative means to keep oil in the bearings. If such an engine were altered slightly, it would run perfectly well with nothing but slash lubrication and the occasional squirt (easy boys!) of oil where needed, such as at the bottom of the piston skirts and the bottom of the cylinder(s).
The key point here is that it is not the pressure provided by the oiling system that causes a hydro-dynamically lubricated bearing to work. Just do the pressure over area vs oil pressure and you will see that 40 PSI, 60 PSI is not sufficient to support either a main bearing or a rod journal bearing in any engine in any vehicle in any driveway. Speaking of mainstream America here- no telling what may be in the Australian outback for example :-)
Brian
Okay then. Explain how 2 strokes work without oil pressure.
where do you get this stuff? It's not just the oil pressure supplied by the pump , but the clearance at the bearing which restricts the oils flow off the bearing and provides the film that separates the parts. This is why proper clearance is so critical. open up a clearance .002", pressure drops, oil film flows off and doesn't separate parts, parts soon go boom. If you've noticed, crank clearances have tightened up since the advent of low viscocity oils. Shell style bearing rely on zero parts contact, whereas roller bearings have constant contact. Shell bearings indeed do rely on oil pressure to separate the parts, case closed. Steve
Okay then. Explain how 2 strokes work without oil pressure.
BDF, I dunno, maybe you're an engineer and I'm a lowly engine builder, but I get the feeling that you're trying to "baffle by bullsh*t"
Here's some info on how oil separates parts on what I'm calling "shell bearings" http://en.wikipedia.org/wiki/Fluid_bearing
If your theories are sound and correct, all modern engine automotive designs are incorrectly designed with shell bearings, because according to you, oil pressure is apparently not needed to separate the parts, but merely provide lubrication. If you are correct, then why are modern engines designed with pressure pumps at all? It's well known that there are power losses due to pumping loss, and any effort to achieve best efficiency would want to rid pumping loss all together. Yet we still have presurized oil systems and shell bearings as the common method of design. what are all these engine designers missing? Steve