So, rotors are usually for the RX-7 are cast iron? The housings are
aluminium with a thin layer of nickel for the wear surface?

Does anyone know what the Johnson or Sachs small snowmobile engines
used for their rotors and housing? I have been told by one person
that the rotors are cast iron too but the housings are just
aluminium.

Does anyone know if just plain aluminium housing are used? Any other
material used for rotors besides cast iron that works?


David Jr.

Yes the rotors are cast iron. Very tough and robust. The housing are
lined with hardened steel and then chrome plated.

There have been many different coatings applied to the aluminium
with out as much success as the Mazda housings. 2.5 million engines
have been sold.

Paul Lamar

Great pictures, thanks Paul. I would take as many of those
production pictures and such that you would like do send.

David Jr.

Here are a bunch more. We were the first round eyes to get a tour
through the factory :-) Took 18 months of cajoling.

Paul Lamar



Great pictures!  I've been working on some investment casting (steel
and aluminum) using sterolithography to generate the wax molds.  It
appears that the rotor would be an ideal part to make using that
process. For ones or twos, it is much cheaper than having to make a
mold.  If larger quantities are needed, then they make a wax mold
from the stereo model. This method sure beats the old way of making
patterns.

Gary Knutson

I made some intake patterns on the local college stero lith machine
back in 2003. In those days the stero lith machine cost $30,000.


Paul Lamar

Could the rotors be 3D printed from say Titanium or other materials
at a realistic cost? The weight of the rotor would be so reduced that
RPM could be increased. The printing would allow a design that would
not be practical or even possible with conventional machining or
casting. I think that NASA is able to print in different metals
without the conventional welding process.

Andrew Campbell.


As long as it can hold the tolerances to + or - .001 inch.

Paul Lamar

It would appear that the tolerances and surface finish of EBDM
printing are of a very high magnitude, the amount of material that
can be deposited in an hour is also high so hopefully costs may be
acceptable. Given the ultimate tensile strength of Titanium alloys
being in the region of 2 times cast iron and a lower SG and the
ability to remove most of the unwanted material within the rotor we
could end up with a %75 reduction in weight.

Titanium has poor thermal conductivity, this would help to keep the
rotor cool, the extra heat not absorbed into the rotor is going to
have to go somewhere though. Would this reduction in rotor weight
translate into a significant power increase?

Andrew campbell

Only if you have a gear box to handle higher RPM.

Paul Lamar


Oooh!  Do I see an opportunity for compound planetary gear reduction?
With two 2.85 planetary gears in series you could run your hyped up
rotary at 14250 RPM.

-  Mark LaPierre

The Rotary Engine News Letter. Powered by Linux.
If you want off the list PLEASE let me know and I will
remove  you.  ACRE NL web site. http://www.rotaryeng.net
You Tube http://tinyurl.com/beqqxas
Copyright 1998-2016 All world wide rights reserved.