It seemed their was a clearance issue when installing the Renesis rotors
in a 13B engine.  Do you recall what it was?  I think the gears, and
bearing may be different as well.

Doug in Japan

News to me.

Paul Lamar



  Paul,

  I'm planning on using Renesis 10:1 rotors in my p-port 20B.  As I
  understand
  it, I will need to cut the apex grooves deeper to accept the 13b/20b apex
  seals, and use only one of the oil scraper rings.  And of course, have
the
  assembly rebalanced.

  Mark S.
  Austin

  http://www.rotaryeng.net/history.html

  Why not run stock low height RX8 apex seals? They have less weight than
13B
  seals so they will follow variations better. Also the RX8 corner seals
  have a very low friction Diamond Like Carbon coating. DLC should be
  applied to all the seals but I think Mazda choose only the corner
  seals to keep the cost down. Seal friction has a significant affect
  on engine efficiency. Particularly at the higher RPM ranges we run.

  Paul Lamar


  Paul,

I was under the impression that there was a risk of the thinner apex seals
catching when passing over the p-ports.  If this isn't the case, then I
agree, go with the Renesis seals.

Mark S.

No the 2 mm seals have been used for years with peripheral exhaust ports
with no problems. The peripheral exhaust port is far harder on the
apex seal than a peripheral intake port. A little slot opens up and you
have high pressure, very high temperature gases shooting out of
there at supersonic velocities. That is the main reason you need apex
seal oil. The apex seal oil cools the apex seal.

By contrast there is no pressure difference across the apex seal
as it passes over peripheral intake port and the apex seal is cooled
by the incoming mixture.


There is another subtle  advantage to our intake p-ports in that they are
oval
so the apex seal is introduced to the opening gradually compared to
what happens in the rectangular exhaust port.

Paul Lamar


 Mark,

As it was explained to me by the guys at Arizona Rotary they use a 2mm
wide apex seal but they cut it the slot deeper to accept the 13b/20b
apex seals. The rational being the RENESIS apex seal weren't designed
with P-ports in mind and as such wouldn't need the thickness- strength
to bridge the open ports. Is it a true statement and does it matter?  I
don't know but it would behove you to speak with several shops that
have done similar conversions already.  I think Mazdatrix has done a
few.  I knew about the need to rebalance but I thought there was an issue
with apex seal length expansion that had to be dealt with during rebuilt.

Doug Fir


Absolute total nonsense. Pure uninformed and uneducated speculation.

That does not make sense Doug.

The load on the apex seal is a function
of the volume of the apex seal times the density of the
material (Cast Iron).

Lets look at the worst case scenario. A 5 mm high seal.

Let's say the rotor width is 80 mm and the slot is
48 mm wide. The volume of the 5 mm seal is there fore 5 x 2 by 48
mm or 480 cubic mm or .0293 cubic inch. Iron weighs about
.3 pounds per cubic inch so that part of the apex seal exposed
to the hole weighs .00879 pounds.

This load is distributed along
the 48 mm length of the apex seal. The centrifugal load is m X V^2/R.
m is in slugs and V is in feet per second while R is in feet.
See the attached formula.

Lets say R is six inches. .5 foot. The rotor rotates at 1/3 engine RPM
so that is about 2500 RPM. The seal velocity is therefore
1 foot (dia) times 3.1416 x 2500 or 7854 feet per minute or
131 feet per second. That is twice as high as Mazda claims.

m (the mass) is weight divided by 32 or .00879/32
or .000275 sligs.

So the load on the apex seal evenly
distributed along the 48 mm length is v^2 or 17,160 times
.000275 / R is 9 pounds. The length is 1.875 or the load
is 4.8 pounds per inch. Check my calculations.

This mean you have a beam with a uniformly distributed load
of 4.8 pounds per inch.

The formula for the max deflection is attached.
http://www.roymech.co.uk/Useful_Tables/Form/Stress_Strain.html

E is modulus of elasticity for iron which is 14,000,000
(14 million) L is 1.875 inches. w is the load per unit
length or 4.8 pounds per inch.

Where "I" is the moment of inertia of a rectangular beam 5 mm
high by 2 mm wide.

Lets just look at the major factors for a moment
and ignore the beam moment of inertia ("I").
L (1.875) to the fourth power is 12.36. 12.36 divided
by 14,000,000 (14 million E) is .000000883!! Divide that by 584
constant and you get .00000000151 inches deflection!!!!

The other factors pale into insignificance compared to this number.

So I am NOT going to calculate them as my brain is
now tired :)

I defy ANYBODY, let alone a bunch of shade tree mechanics in Arizona, :)
to measure this apex seal deflection. Far more deflection probably comes
from the temperature difference from top of the seal to the bottom.
That is probably less on a 5 mm high seal than on an 8 mm high seal.

Check all my arithmetic and find an online beam formula where
you can just plug in the dimensions.

You might try this one but it does not work on my computer.

http://darkwing.uoregon.edu/~struct/resources/applets/beam.html

----------------------------------------------------

As a check on my numbers page 57 Kenichi says the max inertia
load on the seal is 2.6 Kg or 5.72 pounds or 3 pounds per inch.
Less than the the 4.8 pounds per inch I calculated.
That means the deflection would be even smaller.


Paul Lamar

Well OK then, I don't see any need to cut the rotors for 13b seals.  I just
didn't want to start spitting out apex seals over the Gulf of Mexico.

I've set a Renesis rotor onto a 20b side housing and they look to fit and
mesh with no interference.  I didn't measure the gears for variations, but
will do that before using them.

Mark S.

Everything about the RX8 (Renesis) engine is optimized for it's 9000 RPM
red line so it is loafing at 7500 RPM takeoff RPM. With your variable
pitch prop you may see a lot more HP on take off if you can buzz it
to 8000 or 8500 RPM.

What RPM are you seeing in fine pitch now?
How many feet do you need to get off the runway in Austin?
What is the maximum climb rate you have observed?

Paul Lamar