[TR] oil pressure 101

[Randall]

> I've been told, I think, that oil pressure is not like 
> coolant pressure, tire pressure or the traditional use of 
> 'pressure'.

I would not agree with that.  The oil pressure gauge measures pressure just
like any other pressure gauge.

>  It's concerned with volumn (of oil) and the pressure of it.

What I would agree with is that volume of oil through the bearings is more
important to their life than pressure.  Thus, low oil pressure is not nearly
as detrimental as say, low tire pressure; as long as the pump, filter, etc.
are still doing their jobs.

>  It's somehow produced in the oil pump (and measured there?)

Right.  The oil pump creates the pressure (by forcing oil through the
galleries, etc.), and on a TR2-4A motor, the oil pressure is measured where
the oil enters the filter housing.

> and, I guess, pure oil (as opposed to air and oil)

Definitely should be only oil.

> Here the air escapes 
> thru the oil breather hole, and then oil breather pipe? or 
> the more modern pcv valve.

It should be "zero sum", that is whatever the oil pump pulls out of the sump
should exactly match what comes out the other end and returns to the sump.
Thus even if the pump should happen to suck air (which is not a Good Thing
but can happen if, for example, the oil level is low and you go around a
corner), the air does not need to escape from the motor.

> where does oil pressure get measured and how? 
> since the areas are vented?

The pressurized oil is trapped in the various passages, much like water in a
garden hose.

>  If the valve cover area is where 
> the venting takes place, then why is it called crankcase venting?

The main thing being vented is combustion gases that escape past the pistons
and rings into the crankcase area.  From there, the gases can find their way
up through the pushrod tubes to the top of the head, if that is where the
vent is located.  But it is still "crankcase" gases that are being vented,
hence the name remains the same.

> And somebody has talked about removing the breather tube?  
> Why wouldn't that blow out all the seals or something?

It is essential that the crankcase be vented in some fashion.  On some later
motors (after the end of the TR3 run), the open vent to the atmosphere was
removed, and a means provided for the crankcase gases to be sucked back into
the engine and be burned.  This greatly reduces unburned hydrocarbon
emissions.  Unfortunately, the factory solutions were inadequate to handle
the blowby on an even moderately worn engine, particularly at full throttle
when there is no intake manifold vacuum, so these "positive crankcase
ventilation systems" were actually not so positive, and indeed tended to
blow oil past the rear crankshaft seal.

Randall