On the other hand, it is important to remember that if the flow
through the main bearings is excessive, then there will be
insufficient flow passing through the crankshaft drillings to the
con-rod big ends. Downstream bearings only get leftovers! The other
difficulty is that flow is a function of pressure, and if the pressure
is low in the oil gallery for whatever reason, the flow to the
camshaft bearings and rocker shaft will be seriously compromised.
Donald.
> Date: Tue, 15 May 2001 11:41:45 -0400
> From: Douglas Braun & Nadia Papakonstantinou <doug@dougbraun.com>
>
>
> My understanding of this subject is this:
>
> It's not really oil PRESSURE that lubricates the bearings,
> its oil FLOW. The Spit's oil pump (like virtually all of them)
> is a positive displacement pump, which means that the flow is
> mostly independent of the pressure at a given RPM.
>
> The oil pressure that you observe is related to the flow rate,
> the resistance to that flow resulting from the oil being
> forced past the bearings, and the oil viscosity. As the bearings
> wear, the resistance goes down, and thus the pressure. If
> the oil pump itself is not badly worn, the flow rate will
> not drop a whole lot, even if the pressure is way down.
>
> Note that changing to a heavier grade of oil in this situation
> will increase the pressure, but probably the flow rate will
> not change. But at least a thicker oil is a better lubricant.
>
> In a nutshell, low oil pressure is more a SYMPTOM of engine
> wear than a problem in itself. Of course, if you suddenly
> start reading low oil pressure on a engine in good condition,
> there could be a totally different problem, like a clogged filter
> or oil passages (or lack of oil!).
>
> Doug Braun
> '72 Spit
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