RX8 E-shaft vs 13B-RE/REW shaft

[glenrx7]

Originally Posted by vex

That's very peculiar--assuming your correct one should be technically able to ship out the eccentric shaft and have it tempered. However, bending an E-shaft would seem counter intuitive if I'm imagining it right. Where exactly was the bend and how did you measure it, was the bend .006" from the front or was the measurement dictating that the shaft was out of spec by .006" in the front?

I ask because I would be very surprised that the stresses seen are orders of magnitude higher in a turbo built engine compared to the redline of the eight. Do we have the material mazda uses for the E-Shaft (what specific steel they use, etc)? I'll be happy to look up the stats on the material and see what forces would need to be present in order to deform it. I would also think that the REW's shaft would endure more stresses since it's rotational impulse is higher than the 8's (the .6lbs being more weight that needs to be spun up and down depending on the throttle puts more axial stress on the bearings--though the .6lbs may be of no effect or worry).

While doing google searches I came across this:

This is for 20B engines, but I believe the principle is still applicable. Was the original engine Pinned or Doweled?

Ok, well some of your logic is flawed. The rx8 is an na engine with a low combustion pressure putting less stress on the shaft. You increase combustion pressure and you increase forces on the shaft. So for the sake of argument lets jump into black and white for a second. Combustion pressure basically aquates to torque, if you increase it the tourque will increase increasing the force aplied to the rotor, bearing and shaft. So with boost you increase combustion pressure. So with out the turbo you have less force on the shaft even at 9k.......Not to mention the torque on a renisis is well we all know that ./


Now if the shaft is bent .006 it is out of :mazdaspec" by .0045.


The shaft being bent .006 at one point of the shaft would give you a diameter of .012 meaning the shaft is digging .006 all the way around pushing the rotor out of place destroying the bearing etc.

[glenrx7]

Let me also say that i am not sure what torque rate you would have to exceed to bend this shaft but I know 300+ and you are going to be in trouble I doubt chadwick is anywhere near that..


I hope this all does not sound defensive I am about as articulate as a 3 year old on acid that lots there mommy....That s why I do not teach.

[TitaniumTT]

Originally Posted by glenrx7

Nothing over 8k, here is the deal my man. It being harder is the issue. If you have a hardened piece of metal you need to temper it in order for it to be able to have "memory" with out memory it will bend and stay that way. Tempering will soften it in comparison to a non tempered hardened shaft.

Shaft deformation is something that is natural and will happen.[/quote]

I wonder if the tempering is the reason why the 8 shaft is so much cheaper than the 7 shaft.

Do you remember what the clearances were on the main bearings? Could it be possible that some slop in the mains allowed the shaft to flex?

Originally Posted by glenrx7

Look, I dont want to brag or try and make my self look great or anything like that I try and stay humble, to help you out let me give you a little background info.

I was trained to build the top racing rotary engines by Paul Yaw of Yawpower. I built all the engines that came out of his shop for the last 6years or so. Paul moved on to motec and injectors so no more engines, He helped Tom and I start azrotaryrockets.

We are also "sponsored" if you will by Mazda, i act as tech support for there rotary team and motor sports team.....

After coming from Yaw Mazda came with us, they send us project and customers, so I would say we know a little about this subject.

So take my word or dont ...I was aiming to help thats all....Good luck.

I appreciate the help. It's rare to get someone on the internet with actual knowledge and experience as opposed to spreading lore and rumors. Honestly, thanks for the advice.

Originally Posted by glenrx7

Ok, well some of your logic is flawed. The rx8 is an na engine with a low combustion pressure putting less stress on the shaft. You increase combustion pressure and you increase forces on the shaft. So for the sake of argument lets jump into black and white for a second. Combustion pressure basically aquates to torque, if you increase it the tourque will increase increasing the force aplied to the rotor, bearing and shaft. So with boost you increase combustion pressure. So with out the turbo you have less force on the shaft even at 9k.......Not to mention the torque on a renisis is well we all know that ./

Yeah, pretty much my thoughts exactely. The combustion pressures and the torque produced by a turbo-charged rotary are going to be far greater than the torque and chamber pressures places on an N/A engine regardless of how high it spins

Originally Posted by glenrx7

Let me also say that i am not sure what torque rate you would have to exceed to bend this shaft but I know 300+ and you are going to be in trouble I doubt chadwick is anywhere near that..


I hope this all does not sound defensive I am about as articulate as a 3 year old on acid that lots there mommy....That s why I do not teach.

I didn't take it as defensive at all, so no worries.

I would suspect Chadwick is right around there. I should be abour 300 RWT and keeping it under 8k for sure. We'll see what happens I guess. I have a friend making ~450 RWT with that shaft and hasn't had any problems so

[albertomg]

Thanks for the input Glenn

[vex]

Originally Posted by glenrx7

Nothing over 8k, here is the deal my man. It being harder is the issue. If you have a hardened piece of metal you need to temper it in order for it to be able to have "memory" with out memory it will bend and stay that way. Tempering will soften it in comparison to a non tempered hardened shaft.

Harder metals have a higher tensile resistance but a lower ductile fracture point: more likely to break than to bend--but this isn't always true depending on what metal is used, hence why I asked if you had the specific steel name on hand.

Spring back of a shaft would not stop damage to the bearings though--Will it reduce the problem; sure. Will it be the end all be all of failure. I don't see it. By bending the shaft in the first place that means in unequal force was applied to the two different combustion chambers at one ignition event (assuming balanced shaft). That would dictate to me that the flame front propagation produced more force directly perpendicular to the lobe than the other ignition events. Since the RX8 shaft has material removed from the lobe that would cause an "abnormal" ignition event cause the probable deformation. Further running the engine then increased the problem and eventual destruction.

Look, I dont want to brag or try and make my self look great or anything like that I try and stay humble, to help you out let me give you a little background info.

I was trained to build the top racing rotary engines by Paul Yaw of Yawpower. I built all the engines that came out of his shop for the last 6years or so. Paul moved on to motec and injectors so no more engines, He helped Tom and I start azrotaryrockets.

We are also "sponsored" if you will by Mazda, i act as tech support for there rotary team and motor sports team.....

After coming from Yaw Mazda came with us, they send us project and customers, so I would say we know a little about this subject.

So take my word or dont ...I was aiming to help thats all....Good luck.

Wasn't aiming to discredit you, but I don't see the shaft as being the problem but a symptom of an underlying cause. Was the event spontaneous or did it occur at a specific location during a pull? For instance were the HP/Trq curve climbing as the other runs then all of a sudden stopped climbing as previous pulls had become? Or did it occur after a run that was normal, then never pulled the same? I ask because the timing events may have dictated the cause of failure.

Originally Posted by glenrx7

Ok, well some of your logic is flawed. The rx8 is an na engine with a low combustion pressure putting less stress on the shaft. You increase combustion pressure and you increase forces on the shaft. So for the sake of argument lets jump into black and white for a second. Combustion pressure basically aquates to torque, if you increase it the tourque will increase increasing the force aplied to the rotor, bearing and shaft. So with boost you increase combustion pressure. So with out the turbo you have less force on the shaft even at 9k.......Not to mention the torque on a renisis is well we all know that ./


Now if the shaft is bent .006 it is out of :mazdaspec" by .0045.


The shaft being bent .006 at one point of the shaft would give you a diameter of .012 meaning the shaft is digging .006 all the way around pushing the rotor out of place destroying the bearing etc.

I'm doing a little digging on it because I would find it peculiar that the shaft itself would spontaneously become out of spec.

I'm not sure where this data comes from originally but it might become useful in this discussion. The original website is: http://www.rotaryeng.net/Rotar-v-Piston.html

If we assume that to be an NA style 13B then I don't see the Turbo variations being order of magnitudes bigger (where the NA reads 170 kg/cm^2, the turbo will not read 1700 kg/cm^2).

Originally Posted by glenrx7

Let me also say that i am not sure what torque rate you would have to exceed to bend this shaft but I know 300+ and you are going to be in trouble I doubt chadwick is anywhere near that..


I hope this all does not sound defensive I am about as articulate as a 3 year old on acid that lots there mommy....That s why I do not teach.

It's not defensive. If I'm coming off accusatory I apologize, but I think the problem is before the bend of the shaft.

[howard coleman]

just cruising around and bumped into this thread. i am scratching my head as my friend Jose Le Duc runs RX8 cranks and he is making over 1000 rwhp. a couple of weeks ago he ran a 7.50 at around 180 mph. he leaves the line around 10,000 rpm.

hmmm.

hc

[glenrx7]

Well I must be wrong ....Hey Howard please use rx8 shafts in all your builds...Thanks

[glenrx7]

You guys can take it or leave it, the fact is I would not use an RX8 shaft in anything making real power......I would rather be safe than sorry.

I have had more sit downs with the actual mazda na engineers than most, I think i will stand by there data and Yawpower data than "my friend did it"

[REVIT93RX7]

I agree, imperical data is the only way to go with these issues. Drag cars typically rebuild more often than any road going car would. So in there case they don't care about longevity.

[TitaniumTT]

No, they don't care about longevity but the loads exerted on an e-shaft in a 1000 RWHP car (even one revving to 10,000+RPM) are going to be more than that of a 375 RWHP revving to 8,000. I still think something else may have contibuted to Glenns failure, what? Who knows.

I agree that imperical data is paramount, however, can't one argue that an 8 shaft has stood up to this amount of torque for so long and hasn't bent, be considered imperical? Regardless of the temper in the shaft and it being more prone to bending than a 13B shaft, that's still a hell of a lot of load.

[jkstill]

Unless we're discussing royalty, it's 'empirical'.

[vex]

More food for thought (or fuel for fire)

[joff]

Originally Posted by vex

More food for thought (or fuel for fire)

Where'd this figure come from and would you mind explaining?

I assume these are the forces on the stationary gear that would otherwise cause it to twist? How is this relevant to E-shaft loading? I'm just a genuinely curious lurker -- have no credentials for an opinion, and no data points to offer so feel free to ignore...

[REVIT93RX7]

You're just missing the point. But I think what we need here is more data. The more people that use the parts from the 8 in the 7 the more we can learn. My only thoughts here was whether longevity was an issue for you or not. So I for one would like to see some success with these parts. FD engine parts are becoming very expensive. The more parts the better. So let us know how succesful you are with this setup.

[joff]

Originally Posted by REVIT93RX7

You're just missing the point. But I think what we need here is more data.

I agree more data is always good, but I think Glen has a very unique and valuable perspective here -- he actually broke one and followed up with Mazda to understand why and found something very interesting about tempering that has not been brought up before and should not be forgotten.

The facts I didn't know that I've gathered from this thread:
1) RX8 e-shaft is cheaper than RX7 one
2) RX8 e-shaft is lighter.
3) RX8 e-shaft was designed for a car that makes much less torque than the RX7 ever made.
4) Mazda does not temper the RX8 e-shaft, but does on the RX7 one.
5) An RX8 e-shaft has been broken by a prominant engine builder.
6) Tempering, as an extra step in manufacturing, inevitably adds cost.

Fact #5 proves that whatever was the particular failure mode experienced in Glen's build, in that particular instance the RX8 e-shaft was the weakest link.

Fact #6 brings into question the presumption that the RX8 eshaft is cheaper because its newer, as being cheaper because its cheaper to build actually makes more sense when it comes down to it IMHO.

Wikipedia has this to say about the process characteristics of tempering. Apologize if everybody already knows this, I personally did not:

1) Improves ductility and toughness
2) Reduces cracking
3) Improves machinability
4) Increases impact resistance
5) Improves malleability

#4 seems especially like something that might be good for anything inside an internal combustion engine.