Paul,

The following was copied from the 6/02, issue 72, of a Contact! magazine
article on the Renesis engine.

"DYNAMICALLY BALANCED ROTORS  To further refine the superior balance of
the twin-rotor  configuration, Mazda shifted from the previous static
balance setting, and instead adopted dynamic balance calculated from the
mass of oil entering the rotors."

"With the previous rotary engine, the direction of rotation of  the
fixed gear locating the rotors in the front and rear  housing was the
same for both rotors. With RENESIS, the  direction is reversed for front
and rear rotors, achieving  smoother rotation and reduced gear noise."

My question. Were you aware that Mazda used only static balancing on
prior engines? There has been some off line discussion about the
necessity of  a "wet" balance. Nice for perfect balance, but necessary?

The second paragraph, above, appears to be gibberish to me. How say you?

Fred O.

I don't think it was ever statically balance. You don't need
balance weights for that. Put the E-shaft on two knife edges and
the rotors alone will balance each other out. Adding the counter
weights dynamically balances the engine.

Well it is probably an accurate quote from Mazda PR so those people don't
always know what they are doing as they are translating from what the
Japanese engineers tell them. There are a lot of those types of obvious
errors in Ken Yamamoto's book Rotary Engine as well. I was given a CD in
Japan with all that PR stuff on it. I basically ignored it.

 Maybe J.D. on here wrote it :)

The big change in the RX8 rotors is how they are cast. In the old
days, prior to the RX8, they cast the rotors from one side. That led to an
inherently un-balanced rotor due to cast iron density variations that had
to be balanced by milling holes in one or more apex areas. Now the RX8
rotors are centrifugally cast from the center. Here is a pic
I took at the factory. Ironically that led to a crack in the notch
that located the RX8 rotor... rotor bearing :) Since fixed I am sure.

Wet balance?... maybe at 11,000 RPM. I suspect the amount of oil in
the rotor is a function of RPM. The question is: how much weight
do you use to simulate that?

My RX8 shift lever vibrates slightly at idle
at low frequency because of the two torque pulses per rev. Nothing
you can do about that except add more rotors :)

Paul Lamar ...No rotor no motor.

Fred O and Paul,
Balancing is of a particular interest to me and if anyone can confirm or
deny any of the following I would be interested.
It would appear, from what I have been told that the American experts advise
that the rotors must be full for Dynamic balancing.  I have achieved this by
spinning-up the rotor in a lathe and adding oil until it starts to ( ever so
slightly) spill out of the sides( dynamically full). This quantity of oil
represents a weight - each rotor type is different because of the difference
in the cavity.
I have discussed this with a local balancing chap who is undecided,  (but
uses a full static weight) he's also undecided on what components like seals
are part of the balancing weight.
The difference ( in weight) between rotor codes are unknown to me but their
quite small - so a small amount of difference in weight makes a important
difference in smoothness, as it would seem Mazda considers it so.
The local balancer hasn't been as successful as some people would like - as
quotes  like " not as smooth as factory balance' are common.
Any further information would be appreciated.
George ( down under)

The oil should be included as well as the seals and springs.
The question is how much oil? Rotating the rotor in a lathe is not
how it works in the real world. I suspect the amount of oil in
the rotor depends on the RPM and the oil pressure.

As you can see from this diagram the oil moves around inside the
rotor in mysterious ways.

BTW I recommend people download the pdf of the books Rotary
Engine from this web site:
http://www.wankel.net/~krwright/cars/rx7/manuals.html
It will answer most questions on rotary engines.

Paul Lamar ...No rotor no motor.

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