Paul, you had me wondering with your response because I'd recently talked
to Dave about this subject. I called him back and found out exactly what's
happening. Mazda refers to it as a metering pump, and it could be
considered a pump, but it really is truly a metering device, because it
controls the amount of oil going to the apex seals. The oil for the
metering  pump reservior is supplied by the engine oil pump thru a very
small opening which is relieved (vented).

There is virtually no pressure in the system because only a very small drop
of oil is required to lube the apex seal. We could argue if there's any
pressure in the reservior, but it really doesn't matter, does it.

Chuck Harbert

Yes it does. There are no two ways about it. It is not pressurized from
the engine oil pump. The reservoir operates at atmospheric pressure. That
is one reason Richard's adapter works so well.

Paul Lamar

I agree with Paul on this one.  Note that 2-strokes use variations of
this same design, and there surely is no engine oil pump on 2-stroke
motorcycles and snowmobiles (hybrids aside).  This is indeed a variable
stroke PUMP.  I had this wrong for 30 years until Tracy and I had this
conversation a couple of years ago.  It took him about 20 seconds to see
the errors in my thinking.  I had thought that 2-strokes use vacuum to
PULL the oil thru the device - he shot that idea down when he pointed out
that at WOT (wide open throttle) there is no vacuum, yet that is precisely
when the most oil is needed.

Ken Powell

 
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