So here is how this idea came about. Some of the local club members and I went to help another member pick up an 89 GTU. On the way back I'm think to myself " Hmmm, why don't the rotor housings have some sort of integrated water seal instead of the crap factory ones ( crap being relative ). Then I think well, I'm going to ask the guys what they think about this potentially new idea. So I do, and generally the idea seems like it could work.

Here is the theory. If the aluminium housings had an actual machined surface to mate with the side plates that could hold water pressure when the car is off and cold and when at operating temperature would expand enough to ensure a solid seal when pressurized but not enough to crack the water seal grove' wouldn't this in fact be a permanent water seal? Admittedly this is just a theory but wouldn't the tension bolts be able to provide enough compression to allow this? and the water pump is somewhere between 12 and 35 psi so that's not really alot of pressure all things considered. The integrated seal would be matched to a side plate after the initial tensioning of the bolts. Thermal expansion works to make sure water stays out of the combustion chamber and it's metal.... You literally can't blow it up if you overheat it because it's contained in the groove. It's not like your going to melt the metal compared to a normal seal I think this would be a much more reliable and sturdy option. Even if they weren't integrated into the housings How about one that you could use instead of the Teflon and viton seals. .

Think of it this way. when your engine pops what usually is the cause of the rebuild ? The water seals. If the seal is part of the housing and your reasonable with your tune there isn't really a reason the apex seals should ever go. Oil control rings... yea eventually. Side seals sure but you should be well into the 100K plus mileage on the engine. If this is something that could work or at least be tested couldn't this actually change the way we rebuild our engines? I mean what the worst case scenario? The engine seals itself too well or not at all. The best' something you can't blow up unless your doing something really drastic. with your tune. Anyway, opinions from those more experienced than myself are welcome.

 

no one?

 

The issue I see with that is you will not have a perfect sustainable seal with a metal-on-metal connection. Even if it was "tongue and groove", or whatever youd like to call it you will still need some soft seal (gasket) to make a watertight fit. Even then I doubt it would last long with the constant and differing thermal expansion rates. The other items you mention (apex seals, side seals, etc) are wear items, and are constantly being eroded during the engines life cycle. Plus they do not require a 100% seal. Even with tight tolerances a slight amount of blow-by or compression loss happens with those types of seal.

 

So lets assume this is on an all aluminium engine. All the parts are expanding at the same time . As for the lack of a completely water tight seal. How about something similar to a crush washer.

 

closest to what you are referring to is a copper gasket between the housings, which was originally designed by a Barnett rotorcraft in the 70's. i never actually had seen his gaskets as they were made for older 12A engines and he had been retired for some time before i had even heard of him. he recently died and all his shop equipment and engine parts liquidated(before i realized he had died, apparently he had worked on my '74 REPU though so who knows, i might find a surprise or 2 when i pull it apart).

sandwiching aluminum to cast iron won't provide a water tight seal when cold versus warm.

 

Karack, your on point with the copper gasket concept.

 

how about a hollow metal oring filled with a hi-pressure gas(nitrogen), that expands as it gets hot , yet stays flexable when things move around.

they are available and can be ordered in any size!

 

until they wear and blow out like an old tire.

mazda actually did not do bad by using a square cut high temp silicone seal. i'd actually like to see many aftermarket seals outlast the factory ones. people just tend to complain about them because their 15+ year old seals finally failed, which is going to be hard to beat even with all the private companies trying to develop something to outdo them.

the basic fault isn't generally with the coolant seals anyways, because they hold up fine for 5+ years even in race prepped cars. the main fault is the weak cast iron apex seals shattering with moderate detonation levels and the weakened/aged cast iron end plates failing which kill the coolant seals prematurely.

how many engines have i torn down to replace the water seals on after i rebuilt them? in 8 years i have done it 3 times, one where the alternator belt snapped and he drove the car until it shut off. second where a radiator hose broke and lost all coolant and drove until it shut off, 3rd was an aged iron which broke a coolant seal wall after 9 months.

 

ever thought of cutting the grooves into more of a semi circle. I've just been staring at popped engines all week so this is where most of this train of thought is coming from. I do see alot of failures similar to what your describing though Karack, and completely agree with you.

 

well in all honesty, since i doubt i will be doing this much longer i already posted my project for my coolant seal savers in the second gen section here:

https://www.rx7club.com/2nd-generation-specific-1986-1992-17/why-do-coolant-seals-fail-some-answers-you-should-know-953847/

that will take care of half the problem, regardless if people want to think it is janky or not it should and will work as preventative measure for the iron wall failure issue.

for apex seals, it's simply a matter of choosing the correct ones for the application you're building the engine for. there are plenty of seals on the market that can take far more abuse than the OEM seals and so far have comparable wear characteristics.

to keep the engine from twisting above 600WHP, dowel pinning or larger tension bolts are a simple step to completely solidify the engine.

all those things combined= about as bulletproof of a rotary as you can get, and that is how i would build my motors if i wasn't just a small fish of a shop. you don't need anything fancy to push a 13B beyond 1000 horsepower except those listed, lots of fuel and a big *** turbo.

in the third gen section under a similar thread me and Banzai argued the root cause of iron failures, but in all honesty i don't believe he is 100% correct that it is simply a bad coolant issue. look at the iron i pictured and tell me that iron looks like it was old, weakened by acidic erosion, whatever you want to call it... the iron was in decent condition yet 2 walls broke.

 

Well I'm with you on the small fish shop thing. My shop isn't even 3 years old yet, and the vast majority of my work is done in my home garage unless it's something that I really need a lift for. You are 100% on what needs to be done to push an engine deep into the triple digits although I'm not a big fan of doweling. As for apex seals I'd say ceramics are about as good as it's going to get in the foreseeable future unless someone comes up with some high temp carbon based awesomeness that doesn't shatter and cause catastrophic failures like ceramics. As for reinforcing the coolant passages. I blame Mazda for this. I'm pretty certain that there was some sort of special casting done for their 4-rotors to make sure this wasn't an issue for them. Although I have no proof. But really how difficult would it have been for them to just make the lands ( I call them lands) a little thicker. Hell. they could have been twice as thick and circular instead of square-ish...... Maybe I should look into that. If it comes down to a simple formula of coolant volume + pressure = required circulation to keep the engine cool; then I don't really see why circular passages weren't used in the first place. If anything they would at least strengthen the engine somewhat.

 

i don't know why mazda didn't recast the housings, but it really wasn't a huge concern for them at the time. the irons lasted over 10 years in almost all cases before these issues started to arise and were not foreseeable by them so i can't blame them for not envisioning it.

ceramics are the longest lasting as they cause literally almost no rotor and rotor housing wear but they really aren't as durable as you would think. the only reason they are only slightly more durable than OEM seals is because they are made of 1 piece which eliminates the sharp edge of the long apex seal which usually is the weak point of the multi piece apex seals. problem with 1 piece seals is they have very low dynamic sealing characteristics at low engine RPMs, so they cause starting issues in daily driven vehicles but are great for endurance prepped engines that only start a few times during a 24 hour race event.

there are a few durable multi piece apex seals out there now, the most popular 2 seem to be RA super seals and the Goopy racing seals. both of which will bend before breaking which should cause no internal damage to the engine, ceramics when they break cause catastrophic failure even worse than the OEM cast iron seals.