The Metering Oil Pump - Did You Know That a Rotary Engine is Lubricated Like a Two-Stroke?

 The rotary engine is an amazingly elegant machine.  With only 7 moving parts and much less mass and space than any other engine concept, it makes amazing power from a tiny displacement.  In fact it's so remarkable that Mazda bet their future on it in the 60's.  The plan was to use the simplicity to have a lower cost base than their competitors.  The advantages in size and weight would also allow more competitive vehicle designs.  So they purchased a license to the base patents and set about bringing the concept up to industrial specs.

This proved to be a difficult journey.  The amazing elegance of the engine is matched only by the unique challenges it presents.  Chief among these are the apex seals on the rotors.  The seals along the sides are easy to lubricate with oil jets and splash.  The apex seals however, are cursed!  They live on the line between each cycle: intake-compression-combustion-exhaust (or suck-squeeze-bang-blow, which is easier to remember!).  Not only that but they have extreme sliding speed to deal with.  Mazda tried many materials and coatings but, at the end of the long engineering day (and, in Japan, that's a long day indeed!) the only answer was to provide continuous oil lubrication as the seal enters combustion.

In spite of my brother owning an RX7 and an RX8, I had no idea that this was the case but each rotary has an oil metering pump.  This pump is driven by the crankshaft and takes oil from the sump and slowly weeps it into the rotor housing to preserve the apex seals.  This poor compromise is likely the life and, eventual, death of the rotary.  It's a bad idea to use regular engine oil as a two-cycle type lubricant.  It's not designed to burn at all and doesn't burn ash free as a result.  It also has to pass through the catalytic converter, which does not appreciate contamination!  It also requires more frequent oil changes.  Actually, at the rate that BB is burning MOP oil, I'd think one would have to change the oil every 500 miles!

The best engineering answer would be to have a separate sump of clean, two-cycle oil that burns ash free.  But Mazda couldn't imagine asking customers to fill a separate oil tank every month and they were likely correct.  But the compromise probably shortened the life of the rotary as emission regulations increased.  In any case, I thank the inventor and the many engineers who worked to make my engine so fun to drive!

And for the unique problem with which I was confronted!  For the MOP happens to protrude out the passenger side of the engine, right into the frame rail of an MGB.  No hard feelings!  Which engineer designing that could have even imagined such a marriage but here it is.  I didn't want to cut anything out of my frame rail as my main goal is autocrossing, which relies on chassis stiffness.  So, I decided to relocate the pump and drive it with a separate electric motor.  Sounds simple but probably used up about 10% of my time on this job.

Above you can see the manifold in mid-machining.  It was tricky to connect the pump inlet and the pump overflow together but it seems I managed it.  At least oil is disappearing from the bottle and not showing up on the floor so I confidently assume it is lubricating the apex seals!

I bought a window lift setup and removed the motor.  I then machined a slot into the shaft to drive the MOP pump (which is too many pumps but you know what I mean!).

Below is proof that the motor fits.

And here, the entire motor case is visible.

Below, you can see the manifold and motor in situ.  I was very happy when I took that picture which goes to show you how naiveté can f*&% with you!

Below you can see the shaft seal one must install when one forgets that oil will find a way to the driveway if every possible and impossible path is not blocked!

That does seem to have worked although I am still using MOP oil at a furious pace.  As I said, I wonder if you could go 500 miles without an oil change in a stock RX8 at this pace.  On the other hand, I guess I am enjoying some pretty high throttle positions with this new powertrain!

Hopefully, you've a car that begs for throttle as well!  Keep on having #funwithcars !