Jeppy

What RPM does the apex seal start to bounce and why exactly does this occur?

When the speed is reached, at the apex of the compression stroke, the apex seal will bounce because the springs cannot keep up with the RPMs. Is there any solution to the problem currently?

If any developments could be made, my assumption is that the springs would need a way to adjust for the RPM flutter.

If I can figure out exactly what is happening I may be able to simulate and solve this problem using SolidWorks or COMSOL. I can get accurate 3d models of all the components and import them into the software for analysis. I am a skilled with these programs and if the RX7 community can help I am sure I can provide a solution. If harmonics are at play as I am thinking, than finite element analysis will work.

peejay

It depends on the seals used.

On the 3mm seal engines it starts at 6200. On 2mm seals it doesn't seem to do it at all, nor with the lightweight carbon-aluminum apex seals.

It's easiest to just run carbon-aluminums if you're going to wind the engine out. Or bite the bullet and get a 2mm seal engine. The heavier seals overcome the damping effects of the spring and the gas pressure on the backside.

I am running 2mm seals clearanced to Judge Ito specifications, so far no problems and it's been run beyond the end of the 9000rpm tach in MegaTune a few times, and sees 8500+ regularly. Atkins seals, 'cause I'm cheap. Cryo-treated, 'cause I'm paranoid and don't like spending money if I don't have to.

Jeppy

Thank you for your response.

I believe you are correct, this would explain why.

The reason I went with the Hurley seals is enlarged corner section which spreads out the force of the spring into a much greater contact area of the rotor housing. This is why the seals are better for the life of the rotor housing. These seals can be used with regular 3mm springs as the corner section of the seal is shaped much the same way a stock 3mm seal is shaped, at least on the bottom side of the seal which is where the spring is perched.

Another thing to check out... and one that I plan on getting done to my next set of rotors is the Hurley Direct Tip Seal Lubrication System. Often times over the life of a rotary engine the seal, or seal groove, will wear to the point that it is out of tolerance causing the seal to bind and break at high RPMs. I am hoping that this system will provide much needed longevity in this region. " - Tom Walsh
----------------------------------------------------------------------------------

I have been using Atkin's Rotary's apex seal in the engine I build for some time now. I really like them, as they seat so much faster and cause less damage to rotor housings than Mazda factory seals. However, I detonated my engine the other day and one let go (totally my fault, I can not/will not fault the seals).

I am considering using John Almeida's (sp?) ceramic seals from Powerhouse Engineering. I was wondering if anyone has used these before, what their opinion is vs the Iannetti seals that are approved by MazdaComp, what is the wear characteristics of the seal, and how much boost was run. I spiked my boost (accidently, one missed keystroke on the PFC will cause a rotor and housing to turn to slag) to 18psi (ooops) with no other fuel enrichment other than what was programmed for 12psi.

I am hoping to prevent this as I have been told by some that these ceramics seals will take much more abuse (having to tune an engine without realtime, high res A/F ratio monitoring on a chassis dyno constitutes abuse IMHO). Please do not respond if you have not used ceramics seals in your own motors in the past or have spoken directly with those who have (IE. no hear-say please!). If you have information on these I would like to speak directly to you via Phone as I have quite a few technical questions if you have the time. -Michael Gurgainers
----------------------------------------------------------------------------------
Ok does this mean that the ceramics are more durable and all around the best?

Most will advocate using the ceramic seals for only high boost turbo applications. I did notice that the 3 and 4 rotor Kudzu chasis Can Am cars racing at Daytona (normally aspirated) were using them. I think the motivation for the above advocation is due to the cost alone.

The advantages in any engine are that the ceramic material used has a lower coeficient of friction than the more conventional ductille iron seals, and the material is a lot harder. The lower friction, means less wear to the surrounding parts (apex seal grooves, rotor housings, and side housings), and less wear to the seals due to both the lower friction, and harder material. The wear characteristics have been described to me as negligable, but initially enough for them to break in correctly.

Other advantages, are that the ceramic material has less physical mass, so requires less spring pressure to keep them in contact with the rotor housing surface at a given rpm, plus due to the lower coeficient of friction you can use more spring pressure without causing an appreciable increase in wear. Either one of the above means the engine can run at higher rpms without the seal floating, which can cause hot exhaust gasses to travel back into the intake cycle of the other rotor chamber and cause pre-detonation which is one of the major concerns in any non diesel engine.

Stock apex seals can overheat, and warp which is not a concern with the ceramic seals. The ceramic seals although not indestructable, can take a lot more detonation than stock seals. They can also stand up to a lot more boost/power output.

Now for why people stray away from them: ceramic 2 piece 2mm or 3mm seal set costs $1770, plus in the case of the 3mm seals you have to buy double the number of apex seal springs. You could go for the single piece 2mm or 3mm seals for $1200, but will have less compression under 4000 rpm over the 2 piece seals.

After getting past the 'you don't want those!...why not?...because they cost a lot'....banter, I have heard from several rebuild places, and Franchesco Ianetti himself that when it is time to rebuild the engine, you can re-use the ceramic seals over and over again (the gift that keeps on giving?).

I have seen and heard about far too many rotary engines where either the seals break from detonation, or wear out the rotor grooves making the seals not fit properly, and eventually breaking the corner seals (non solid corner type seals where Mazda thought a piece of rubber might prevent this), and doing major damage to both the rotor, housing, and turbine wheel. The cost of doing a premature rebuild alone is enough to make the cost of the ceramics seem like a bargain, plus the cost of the damaged housing/rotor..then add in the amount of pain and suffering you will go through when the mustang you were racing when the stock seals went beats you -NetBlazer

-www.fd3s.net/apex_seals.html

So the problem is pretty simple. The 2mm seals are smaller and the ceramic is lighter. There is less inertial mass and the RPMs can now go above 9000-10,000RPMs. The lower coefficient of friction reduces the wear and tear to all parties, and the corner seals still perform very well at the high end RPMs.

The price is worth the performance, basically....

Please read through the referenced website: www.fd3s.net/apex_seals.html
If there are any other considerations I would like to know.

peejay

The triangle piece doesn't cause the grooving. I have pulled OEM-assembled engines apart with grooving only on the "front" of the housing and not the back. The corner piece is always at the back when the factory assembles an engine. I have also pulled apart an engine that had the corner piece so worn out that it was button shaped and the spring was wearing into the rear and center housing, but no more grooving than is normal.

Housing movement and expansion/contraction causes the grooving, as the chrome gets fretted away from the edges the seals will wear a small lip there.

I do not like the enlarged corner piece because as it expands, if it has insufficient clearance to stay "flat", it can lift off significantly. It would also seem to put more stress on the apex seal as it passes over the exhaust port, as proven out by the standard Hurley seal death mode (as of 2002-ish, anyway) of breaking off a triangular chunk of the long piece.

But, other people run 'em, and I just made sure my exhaust ports weren't extremely wide. On my P-port they go to within 7/16" of the housing edge. I wouldn't do that with Hurleys, or Atkins.

Jeppy

So the ultimate improvement to the 20B would be a ceramic housing and ceramic apex seals. The ceramic layer reduces thermal conduction significantly, and performs as a self lubricated material because the brazed copper melts on the surface.

I do not fully understand the design function of the corner piece, but I will do some research.

I read something interesting about the ceramic housing. It stated that by retaining thermal energy within the combustion you could increase the efficiency of the engine by up to 25%. I found that hard to believe, but I do not understand these engines enough. If thermal loss is high enough the BTUs within the combustion will produce a lower psi output, to a point. But a 25% efficiency boost?

The ceramic housing solves so many problems, but at a very steep cost.

Nearly eliminating expansion and contraction
Minimizing thermal conduction losses
Minimizing friction and wear between the housing and apex seals
Possibly increasing the efficiency and horse power???

I read outfitting a 3 rotor 20B costs around $140,000

Thank you for your input

j9fd3s

iTrader: (3)

i would do some searching for the book "rotary engine" (its on the web) and mazda's SAE papers. they have write ups and graphs and such as to why they chose to do certain things, such as ceramic apex seals.

briefly a 2 piece apex seal can compensate for a change in length, and thus seals better, which improves power, and fuel consumption.

the ceramic coating, as used on the 787B engines, was done for wear and friction reductions.

peejay

I found this pic in one of my image folders, I wanted to bring this thread back up so I can share it in the proper context:




These are from the "Second Most Worn Engine Ever Seen". These apex seals were from the rotor that had compression good enough to drive on. The other seals were just plain gone.

Notice, that the corner pieces are worn tiny, and at the OTHER end of the apex seals, there's a little lip where it had worn into the groove in the chrome. The groove caused that lip, not the other way around.



I bet if the rotors hadn't worn so badly, the seals would have sealed better, not bounced so much, and maybe the engine would have lasted longer than 150k. I have a feeling this particular engine saw a lot of high RPM abuse.