> 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.
Hi Paul,
Mazda has always dynamically balanced their engines and still does.
Oil compensation is an average over the entire rpm range, and is
significant. The amount of oil in the rotor is not constant but doesn't
change a lot. It is continuously "sloshed" out by the rotor motion,
re-supplied by the oil jet and rotor bearing leakage.
Jim Mederer
Thanks again Jim. Being the most experienced person in rotaries
that I know you are a valuable resource to the entire rotary engine
community.
Paul Lamar ...No rotor no motor.
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