Clearances and oil pressure reasoning...
06-10-2004, 10:29 PM
#1
Clearances and oil pressure reasoning... I would like to know if my understanding between bearing clearances and subsequent oil pressure needs is correct. Here it goes:
First, I'd like to set my control as a stock spec engine in terms of bearing clearances. My tested variance is the changed in bearing clearances which will be limited to the main and rod journal bearing clearances.
In order to prevent metal to metal contact b/w bearing surfaces and the metal on the crank and rod portions there must be:
1) clearance - oil filled gap separating the two spaces created by oil via oil pressure fed by the oil pump through the oil gallies in the rods and mains.
In an engine that has "looser", i.e. more bearing clearance (I assume that is what the term means) you have a larger potential space/gap that can be created by subsequent oil pressure, if the oil pressure can compensate enough.
Therefore, with "looser" bearing clearances (in respect to the bearings mentioned above) MORE oil pressure would be needed to create and maintain that "looser" clearance (gap) when the motor is fired up, correct? Therefore, the need for shimmed or increased pressure oil pumps.
If this follows correctly, this is why we need more oil pressure on engines with "looser" clearances, correct?
Why then, do big cube motors need and/or prefer these "looser" clearances(bigger potential space filled by oil that prevent metal to metal contact) in regards to the bearings referred to above ?
First, I'd like to set my control as a stock spec engine in terms of bearing clearances. My tested variance is the changed in bearing clearances which will be limited to the main and rod journal bearing clearances.
In order to prevent metal to metal contact b/w bearing surfaces and the metal on the crank and rod portions there must be:
1) clearance - oil filled gap separating the two spaces created by oil via oil pressure fed by the oil pump through the oil gallies in the rods and mains.
In an engine that has "looser", i.e. more bearing clearance (I assume that is what the term means) you have a larger potential space/gap that can be created by subsequent oil pressure, if the oil pressure can compensate enough.
Therefore, with "looser" bearing clearances (in respect to the bearings mentioned above) MORE oil pressure would be needed to create and maintain that "looser" clearance (gap) when the motor is fired up, correct? Therefore, the need for shimmed or increased pressure oil pumps.
If this follows correctly, this is why we need more oil pressure on engines with "looser" clearances, correct?
Why then, do big cube motors need and/or prefer these "looser" clearances(bigger potential space filled by oil that prevent metal to metal contact) in regards to the bearings referred to above ?
06-10-2004, 10:49 PM
#2
The pressure is a direct result of the clearances. Tighter clearances result in a higher pressure reading as it requires more built up pressure to squeeze the oil between the surfaces. You may be getting adequate oil flow even with lower oil presure readings due to looser tolerances.
