Yvon Cournoyer wrote:
Good morning ;
I offer some thoughts on the use of Mazda's oil metering pump.
By September 1993, after about 100 hours airtime, I had an in-flight
partial
failure of the metering oil pump system. One of the four oil hoses melted
completely through, close to the metering pump, I believe from the heat of
the
exhaust pipes. I found out only after landing. An oil drip alerted me. I
replaced the melted oil hose and installed an aluminum plate as a heat
shield
between the exhaust pipes and the oil hoses.
But, I could no longer entirely trust those oil hoses after that, so, at
150 hours air time, (June 1995), I removed the metering oil pump, hoses and
nozzles and plugged up all the holes. I never opened a rotary engine, so the
metering oil pump drive is still in place inside the engine. <snip> Since
the removal of the metering oil pump system, I was using an oil to fuel
ratio of 1:180, as recommanded by the Racing Beat people.
I now believe this ratio is better adapted to high performance automotive
use of the Rotary. During the winter of 1997-98, I reviewed Tracy Crook's
recommendations and other data and decided to use a higher oil to fuel ratio
of 1:125 in future. I believe this latter ratio is better adapted to the
lubrication requirements of aircraft engine use. <snip>
(Dave Carter says: Here's the good part:)
May 99: As I learn more and more about the rotary engine, (especially on
Paul Lamar's rotary engine net), I wonder about the effect of the oil
metering pump lubrication, on the longevity of the engine in aircraft engine
use.
Mazda's 1986 RX-7 workshop manual page 2-7 state the metering pump maximum
standard discharge of oil at 2000 rpm to be 132 cc/hr. My engines burn 30
litres/hr of fuel, from startup to shutdown, so I calculated that with the
oil metering pump, I was using an oil to fuel ratio of 1:227, on my first
two
engines.
This is very far from the ratio of 1:128 advocated by Paul Lamar and all
and which I agree is entirely necessary if you are going to cruise the
engine at
5000+rpm in aircraft use. Thinking back on my first two engines, which I
ran with only the metering pump and did not add oil in the fuel, I now
wonder to what extent that was instrumental in their failure.
If one were determined to use the metering pump in aircraft use, I
recommend adding two stroke oil in the fuel as well.
David Carter comments:
As the lone advocate of using the stock oil injection system on my aircraft
rotary (with 2 stroke oil in the crankcase), I surrender. With Yvon
Cournoyer's calculation of the oil injection ratio and experience to match,
I am now persuaded to disable the pump and rely only on pre-mixing.
David Carter