Paul,
Interesting conversation I recently had with the local engine

builder on RX8 Parts and their interchangeability with the RX7.

He recently built a RX7 racing engine with RX8 rotors - I thought

the RX8 rotors were quite a bit wider ?

I also thought the bearing sizes were different - but apparently

not !

Anyhow all went well until he got to 10,000 RPM when the rotors

were binding on the endhousings, so they shaved (just a little) off the
sides of

the rotors.

He also noted that the rotor side seals were much shorter( in

length) that RX7 side seals. He was concerned about too muck leakage but
they worked

OK he can

only put down the extra gap in the side seal ( to the apex side

seals) as needed because the side seals were exposed to greater heat of the
side

exhaust and

therefore expanded more!  Apparently some people put in bigger

apex side seals to make up the difference in gap.

Also the apex seals were shorter in height so they cut the slot

deeper and put in Hurley apex seals.

Speaking of Hurley apparently they have a 2 piece side seals (

very thin) which are very flexible and tough.

I suggested using a bi-metal hacksaw blade and grind it down to

size as they are very flexible and tough - the new hacksaw blades out now
don't

break at all.

Cheap side seal idea if anyone wishes to try it.
George (down under)

-> "Powell, Ken" wrote:

George, great info.  I have wondered if you could use the rx8 rotors in

an earlier 13b.  The lighter rotors would allow us to turn higher rpm
safely.  If you

are using a PP intake port this sounds like a less expensive route than

a new rx8 engine.  Looks like you would need rx8 rotors, seals, and
front/rear

counterweights to make this work.  Maybe the 86 - 91 counterweightes can

be used if the rotating assembly is balanced.  Does anyone know if weight
would have

to be added or removed from the counterweights to work with the new

rotors (seems like the weight would need to be removed from the
counterweights to balance

lighter rotors but sometimes things don't work like it would appear at

first)?

Ken Powell-

Dave Atkins had a 1993 3rd gen and an RX8 rotor at OSH. They appear to be

the same weight.

Ken,
I think Paul is correct with that assessment, I don't think you need to
lighten the counter weights with lightened balanced rotors. It's something I
didn't think of and will put that question to the 'boys at the shop' when I
speak to them next.
George ( down under)

Subtle distinction here George. If in fact the rotors are lighter you do
indeed
need to change the balance weights.

Paul Lamar

-Douglas Fir wrote:

Hi George,

The Rotary Engine Press paper I sent you mentioned the Renesis rotors are
lighter and illustration should less material in the inner metal walls.
However it might amount to only a few grams.  Can anyone out there weigh one
for us to confirm it?

Doug in Japan

I can't tell you how many grams but it was about only an ounce or two.
Something less than a 1/4 of a pound. A regular rotor is about 9 pounds.

Paul Lamar
 
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