The part number i needed was fmz004c-cw3 but is unavailable anywhere, shame on companies selling flywheels without their own counterweight needed. The weight i ordered has no available part number just that it fits multi flywheels as a rear counterweight. It was a matter of getting something over nothing. Id come to the conclusion if they all look like ducks and and weigh the same as a duck it must be a duck.

 

I will be resurfacing the OEM Flywheel anyways, but was more for a clean object on the wall as i like keeping all the old parts anyway.

 

This all started as i assumed the clutch was on its way out (wont actually know what the problem is till i take it apart) , cursory reading had said flywheel should be resurfaced/replaced on clutch upgrade/replacement. So here i am at the bottom of the world (Australia) fighting ridiculous dealership prices and back orders of what should be sold togeather

 

yeah, just like the side seals; the idea didn’t work as well as somebody thought it would.
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Spoke to supplier of the weight i needed today, he confirmed as team said that they're basically all the same and the only difference if any is a couple of grams here and there. They arent designed to work with matching flywheels but are "weighted according to the rx8"

 

I think I get what you are saying now. The computer/markings tell them one rotor is a particular weight, and they grab a matching rotor to put it in with, and leave it at that. Looking at my other rotors from older engines they are all balanced on their own axis. My Renesis rotors aren't touched. Am I going to look at the flywheel & it's integral counterweight and find no balancing marks as well?
As for side seals, from what I hear they were always done with the method they used on the Renesis. While I can't find any information on if they were using a similar lettering scheme, I do see kana next to each side seal on older rotors.

 

nope, Renesis rotor weights are all over the board according to my builder who goes through swapping a bunch of them out of PDC inventory and does super critical balancing

which rotating balance on factory engines is also all over the board is what he told me a long time ago

so the idea of the CW being fine tuned really doesn’t mean much in my book, because unless you balance the entire assembly it’s a crap shoot. You’re more likely to win the Mega Lotto than to be anywhere near balanced putting this on any engine that wasn’t already balanced and blueprinted by a builder.
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I believe there is another factor going on here that Mazda knows, and others have not really spoken about. While balancing the entire assembly is beneficial and should be done, and the builders that do it are surely spending their time wisely, the oil sloshing around in the rotors provides a balancing effect, like the LeBlanc balancing ring on a clothes washer, (or filling your motorcycle tires with Slime! ) for the rotors themselves, constantly changing with rpm, which means there is a constant balance/imbalance situation going on depending on how much oil is remaining in rotor cavity, and how much rpm, and thereby centrifugal force, and oil flow and volume is present to force the oil into and out of the rotor cavity.

So while Mazda's weight tolerances seem very sloppy, I believe there is more afoot here as far as dynamic balance is concerned, and Mazda was aware of this in designing this engine.

 

And, I pray that someday, a high ranking Mazda engineer arrives on this site to really give us some backstory on the development of this engine. I have had the great fortune of having two cars in the family where development engineers showed up to lend their insight in forums on the whys and hows during development. Totally fascinating!

 

I like that line of thought Kevin, when you chase minimum or beyond tolerances you may gain something but you lose something else in the trade. That said I don't see the harm in a good balance itself and I know at least several machinists account for the weight of the oil in the rotor during balancing. Of course, they wouldn't disclose to me how they do that...

 

Well I only know what a well established rotary race engine builder starting from the mid 70s told me. IMO the only other person I would even consider possibly equating to his experience with the Renesis might be David Haskell who was at Speedsource. There are multiple dyno graphs posted on here demonstrating his work. The factory results are well known too, ugh.

You want to fill you buckets of hope with that other stuff, be my guest.

I have the original release document from Japan on the RX8 breaking all the components of the car down with profiles of the engineers in each section explaining things. Frankly, I’ll put my faith more in my engine builder than a corporate engineer.

 

I’ll also just add that prior to the Renesis it was understood that a rotary engine should not exceed 8000 rpm without having the rotating assembly balanced. The Renesis had a 9000 rpm redline from the factory and it’s not unusual for people to reprogram that higher still. Further, the rotor balance isn’t just rotational about it’s own centerline. It’s the weight variance between each rotor relative to them both rotating about the e-shaft centerline at the same time. Same builder told me they varied as much as 50 grams from each other Within the same Letter designator. So even though they might be balanced about their own centerline, if one weighs 50g different than another on the same e-shaft that’s going to throw the forces being applied to the e-shaft to not be balanced. Which that rotor weight variance also seen among the earlier 13B rotors too. He also said the front and rear counterbalance weights were not really all that well balanced. So that idea about oil inside the rotor is not going to address those issues at all.
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Wow. 50g? That is a hefty amount. Not as much as a similarly sized piston engine's rocking couple, (a similar type and location of imbalance, I believe) but way more than I would have thought, especially since it can be avoided in production, unlike a rocking couple. There is a guy on here in the oil analysis forum I believe who had an eshaft break. Not sure if it was due to imbalance or not.

They talk about the counterweights here also. No bueno:

https://themotorhood.com/themotorhoo...-rotary-engine

 

Claims can be made that Renesis rotors are balanced on their own axis but I have never seen one that had any signs of balancing. Not sure if you were just saying that to say it but I think it's well enough known at this point. Just looked at your link Kevin and it does say the same. Rebuild time is coming sooner every day.

 

50g is less than 2 oz. in US terms, but as rpm increases it becomes greatly magnified. That and a light flywheel can also cause idle stability issues (hint-hint).

Otherwise, you aren't going to “see” anything (except possibly the end results upon disassembly in the most serious cases) unless you actually carry out the balancing method yourself. That’s the central issue here; you don't fully understand why dynamic balancing is essential for the rotors spinning freely on-center rather than the e-shaft bending/flexing and allowing them to tip over into the side plates (there isn’t a center plate e-shaft bearing, just on the end plates), excessive wear on both the e-shaft and rotor bearings, extracting the last HP out of it (see my dyno posts), and so on. Oil pressure plays a role in that too; another thing people here didn’t and still don’t fully understand why that is in their past discussions of the S2 changes.

Maybe the light will starting brightening some after you read this.
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I think, if your comment was directed at Kimura, was that he was referring to seeing evidence of balancing activity on the rotors at the factory. I think we all can and do agree that balancing is worth the trouble, for most builds.

 

I think it's worth the trouble for every build that you want to be reliable for any length of time.

 

It’s more critical on a rotary than a piston engine imo. First, the rotors don’t really spin; they orbit. That in itself will exacerbate imbalance issues. Also, unlike a connecting rod on a crank shaft, which is a tightly coupled bearing connection, the bearing connection between the e-shaft and the rotor isn’t coupled at all really. The rotor bearing diameter is much larger than the e-shaft journal. The e-shaft journal surface slides along the rotor bearing surface. The coupling is at the gear teeth connection between the rotor and the end plate gears. The two in combination create the orbiting rotor motion as the apex seals transition along the rotor housing surface.

It won’t seem obvious how this is different and why it matters. The easiest way to visualize it is with a new/fresh engine. If you turn the flywheel in the forward direction pushing the rotor along, then stop and lightly reverse the direction you’ll feel a quite noticeable dead spot as the eccentric is turning until it moved the rotor back in the opposite direction. The same thing occurs again if you stop and go back in the other direction, and with every rotation direction change. The first time I ever saw this it concerned me greatly, thinking something is wrong in this newly rebuilt engine. The reason why this is has to due with the non-coupled sliding motion connection between the rotor bearing and the e-shaft journal. There is a clearance between the two surfaces. When the e-shaft direction is reversed it has to transition through this clearance before making contact with the rotor bearing again to move it in the opposite direction. The same thing happens with the crankshaft/connecting rod, but being close coupled the clearance transition from one direction to the other is much smaller and less perceptible.

What does all that really mean? Well consider the cyclic combustion process forces. In rudimentary form for simplicity; as the e-shaft pushes the rotor to compress the intake charge it resists against the e-shaft journal. When the ignition fires, the combustion gases now reverse that force to instead push the e-shaft. Then when the exhaust port opens that force is relieved. Except there are three faces on the rotor and this is all taking place cyclicly on them all at the same time. So on top of that, you have two rotors that are orbiting on a shaft that’s only supported on the ends. When imbalance forces are then added to the equation; what most people perceive on the surface to be this perfect model of things spinning along in perfect, ideal motion ends up in reality to be chaotic cycling shimmying motions and forces that can’t be perceived by eye.

It’s not perfect motion and never will be, but dynamic balancing helps to tame and minimize the situation.

 

if that’s all you got out of it then you didn’t really understand.

 

Clearly there is a lot more to it, it was just a basic statement to show agreement. I follow what you said but either you think I missed something that I didn't, or something went so far over my head I haven't a clue.

 

Apology, my point is that it’s not just reliability.

 

And, I could have this wrong, but somewhere in there there are forces sufficient to produce at least 155 (ish) lb/ft of shaft torque through an (effective) 3:1 overdrive that need to be controlled and routed for output through one shaft, with only 2 main bearings, as you indicated.


Like you said, these engines go hmmmmmmm, but really there is a lot more going on.