living proof, 1988 SE, 187,912miles on the dot. 2mm seals, and the engine still hasn't blown granted I'm counting on it to smash the apexi seal on the rear rotor any day now, but still.... 187k, almost 188.... **** piston motors, I'll drive my 7 until the oil runs dry!

 

Well of course a 2mm seal is more appropriate in your application, I don't think anyone on this forum would question that. Nice to see you getting high miles on the engine though, a sign of proper mainteenace indeed.

 

I had 2 second gens that I revved, raced, rejected, and pretty much tortured to their demise. Both had over 150k miles on them (of which I put about 35k each) Surprisingly the motors never blew (though I tried, many a time) It was the trans/diff/driveshaft that pooped out.

Now I have a 3rd gen, where seals matter more. I am getting 2pc 2mm "indestructable" seals. Ive heard good stuff about them.

Seals

 

there cheap!

 

It Sounds Like Everyone up here on this post thinks they understand why apex seals break and not side seals the fact is the apex breaks because more of the seal is exposed when you have a 6mm tall seal and 3mm of it is out of the groove and you detonate it will break side seals are 4mm tall and only 0.25 to 0.50 mm stick out so therfore it is much stronger due to the rotor reinforceing it un like the apex seal which is exposed and you can break side seals I broke 5 apex seals and 11 side seals in my motor due to a fuel pump failure while on nitrous, 3mm seals are better than 2mm seals if you don't believe me ask anyone who has a 12a or 70's model 13b or gsl-se how many miles they got out of thier orginal motor and you will see these engines lasted alot longer due to bigger apex seals and bigger side seals It seems no one here has done their homework to know this stuff you all believe what you see on the internet and not what is proven to work better. If 2mm three piece seals are so good why did mazda quit using them in their rebuilds and use 2 piece seals? And if 2mm is so good why did mazda use 3mm seals in the kudzu cars? and if side seals arew so strong and unbreakable why did mazda change the design for the renesis to have wedge shaped side seals in stead of straight side seals?

 

I have to clarify myself I had not read all the posts, 2mm seals are fine for moderate levels of boost. think of boost as what it is it's PRESSURE pushing on the apex seals side seals and rotor if you have a 2mm seal then the base is 2mm wide when you let it come up and apply pressure horizontally to it it will strech the groove it sits in and slitghly bend the seal because then is not enough base to spread the force out evenly with 3mm the force is not spread completely even but it does transfer the force better so that there is less fatigue on the apex seal horizontally. there is a reason why the third gen need a new motor between 40K and 70K this is due to the three piece apex seal and the fact they would fatigue and no londer hold good compression ask any third gen owner who has had their car since new when I worked for mazda back in '98 we would warranty about 9 engines a weak for stalling with the a/c turned on this was a compression issue The compression would generally be 6.-7. kgcm and this is all due to apex seal stress from the turbo's. If you don't believe me find someone who speaks japanese and all the engineers in japan and ask them why they changed the 3 piece to a 2 piece and why older 13b and 12a housings are in so much better shape when we disassemable them than fc and fd 13b's it's almost a proven fact that if your rebuilding an fd you are going to new atleast one new rotor housing to build it right and make it idle properly and make good power they eat housings due to apex seal chatter due to apex seal flexing and distorting.

 

CRAP
FD's wear out rotor housings prematurely due to reduced oil injection compared to early engines.
Mazda wanted to increase service intervals from 5k to 15k without emptying the sump!

 

I went through Mazda HQ in Hiroshima last september, and I did ask that question, and the reply from mazda was the slight compression gain was not worth the extra manafacturing costs of the 3 piece seal, in order for the rotary to survive the economic feasability scrutiny, ever part of the manafacturing process was put under the microscope, the 3 piece seal doubled the machining process of the 2 piece seal...In order for the rx-8 top make it to production, they had to find away for the 13b to be as cheap to make as eunos roadster motors.
I think there are to many operating differences between the rx-2 and say fd housings to say they wear out faster due to just the apex seal, the earlier cars were not run under boost, on such low levels of octane, with less omp delivery. the earlier 13b's probably saw leaded gas, which coats surfaces and acts as an impregnating lubricant and cushion surface. Although I have to say I have not seen FC housings with chrome flaking off in the middle of the housing for no apparent reason like use to happen on the older engines.

 

A few years ago along northbound I880 in the southern bay area, burning Shell 87, a friend aboard, I pushed hard in 5th gear to complete a sprint from the onramp to 120mph. I suddenly lost 95% throttle response and the engine stopped buzzing and began flapping. I coasted in gear 5 to an offramp to a hotel parking area.

Rick's Rotary tested the engine as having no compression at the rear spark plugs. This was a stock FC TII (2mm apex seal).

I later observed through the exhaust, the apex seals of this rotor are crumbled and the housing is mildly scored. The seals appear bent before being rolled and torn/crumbled against the rotor housing. The rotor apex area is bent from the seal.

2mm rotor apex slots present metal closer to the rotor perimeter. This apex helps reinforce the seal sides, though it's a thin reinforcement. This reinforcement is also negligible drag along the seal sides, and negligible mass at the rotor apex.

3mm rotor apex slots have less rotor metal at the apex, slightly reducing seal guidance/reinforcement, slightly reducing seal drag (if we disregard the seal leaning in the slot and being gouged by the apex slot-edge). Seal inertia is increased, possibly increasing seal at the housing, but without firmer springs I expect would vaguely or latently contact the housing following compression.

I now use 3mm re-slotts of stock 2mm rotors.

I expect recent 3mm seal alloy such as Atkins's are better with resisting the knocks of pump gas (e.g,. R+M/2 87) with stock emissions settings than 2mm. My old seals show bending before being torn.

 

Dont get me wrong, I'm a die hard rotor head. But you have to give Honda some credit for building some pretty tough little engines.

Example #1: My 1993 Honda Civic Si hatchback. I bought it with 45k on the clock in 2001. I beat the **** out of it on a daily basis. Burnouts, drag racing, practicing 180's, and 360's, bouncing the tach off the rev limiter. I overeved that little 1.6 liter vtec engine on more than one occasion. The worst was a 7500rpm downshift from 3rd to 2nd (missed 4th). That little thing must have reved around 12k. Today the car has 190,000 miles on it, and it still runs strong as the day I got it. Of course I dont drive it very much now. Why would I now that i have my RX-7.

Example #2: My friends 1990 Acura Integra GS. Purchased with 210,000 miles on it for $900 in 2000. The original engine had 295,000 miles on it with no rebuild before we swapped it out for a CR-V engine.

Rotary engines are absolutely beautiful from an engineering standpoint. I appreciate the superiority of rotary design over piston/cylinder design for an internal combustion engine. But you have to give credit where it is due. And in my opinion, Honda has definately excelled in producing powerful (per unit displacement), reliable powerplants.

Im ready for the flames, but i had to put in my 2 cents.

 

Rather than slogging through the whole thread, IMO, it depends on the application .

 

i would assume that someone has pointed out that ceramic seals tear the hell out of the rotor housings when they break/blow and that bits of ceramic can get into the turbos and chew them up as well.

gordon[/QUOTE]

I can not tell you how many times I have heard this. What has a steel seal never torn up a housing or destroyed a turbo?

I can tell you of 2 occasions where ceramic seals have broken due to detonation and didn't cause a lick of damage to anything!!

In fact I have a seal here that broke on one end and the engine continued to run until the same seal broke again on the opposite side and still no damage. This was evident by the carbon visible in the first break and not the second.

Ceramic seals don't always destroy engines when they break.

BTW you can have the best of both worlds with ceramic seals... 3mm seals with the radius chamferred to 2mm contact.

Glassman

 

It's rolling the dice depending on the housing, but if you have a very efficienct plumbed wastegate system, the broken apex seal will almost never go through the turbo itself.

We found this out when we blew a rebuild using brand new Mazda OEM 2-piece seals.
The first time, the apex seal did not touch the rotor housing, and it lodged in the WG valve.
The second time it did take out the rotor housing, but again, it blew out the WG side.
Twice it saved a very pricey Garrett GT-3540.


-Ted

 

I've tried both 2mm and 3mm (hurley's), 3mm makes just as much power as 2mm (negl. difference), and is much more bulletproof. Even the best tuners can't tune for all the conditions, I've seen well tuned street cars blowing up on the track due to excessive heat and other factors. So for peace of mind, go with 3mm.

Or maybe 2mm and water injection...

 

Ok guys here we go you can claim BS if you want but I have all documentation from my little August of '78 RX-7. She was bought by a Navy Caommander in 1978 in Hawaii. She was sent over to the Continental US on her next duty assignment. Next she sold it to a Chief Petty officer who was stationed in a Naval Air Station near FortWorth with over 300,000 miles in march of 1991. He sold it to my dad who is in the Navy who is a Senior Chief in 1996 with over 450,000 miles may I remind you still original Engine now. He gave it to me when the rear end whent out in 2001. He drove that thing from Greensboro NC to Norfolk Virginia almost every week until he had to goto Charelston SC. a round trip to Norfolk is roughly 500 miles. The car now has over 500,000 mile on the original engine with some powerloss. But she is still reliable. She now has an '85 Rear end and runs strong! If I am correct that motor has 3mm apex seals. I am not understanding you guys' opposition to 3mm if my '78 has over 1/2 million miles on the original engine with some powerloss in acceleration but is still strong. Just doesn't add up in my book. But my '83 GSL before it was wrecked lost its engine at around 130,000 miles and was replaced. I don't understand it but in my opinion I think Mazda Produced better engines back in the day to last vs todays engines. Like I said that is my opinion. But still you cannot ignore my '78 RX-7's engine and the miles put on her. I have all documentation from the time she was bought to now and who bought her and the reports from the Mazda Dealerships where she was serviced. From my records up until I got, her only the Dealership serviced her engine needs. I have a whole file drawer just on the '78's Doc logs since August 24 of 1978.

What is up with that. From what you guys are telling me since she is a 12A and has 3mm Apex seals she is a POS and should have broken down 15+ years ago. I am very defensive of my '78 RX-7. She is a good car and in my honest opinion prior '80 models where the best ever produced. I would take a 12A over a 13B anyday based on my 78's standings. But let me ask you guys one question? Is it safe that my '78 RX-7 backfires between 2nd and 3rd gear mainly?


Whats the deal with 3 cylinder metros and 60+ MPG Highway,

Dan

 

You have obviously never driven an 85 supra, they were years ahead with handling before they fucd up and changed body, addin 900 pounds and length. 85 they changed all suspension and a few other things, only ran that set up for a year and a half. 85, and half of 86 fealt more like a go kart than the 7's do. however 85 not very fast.

 

wow thirteen pages already, my bad

 

after that, they turned into the japanese camaro

 

Im sitting on the fence with 2mm vs 3mm but one thing that I dont think has been bought up is the actual slotting of the rotors for 3mm seals, the 2mm slots are going to be much more accurate and have a much better surface finish than a 3mm slot that has been cut using a slot drill or end mill.

 

The most accurate method is a wire EDM and the finish is no problem.

 

But even the most accurate, really isnt accurate enough, not to mention the hardened surface of the rotor is then gone with the milling...

 

Have you ever seen one done????
They have a constant flow of water being poured over the cutting bit and surface of the rotor, with lubricants and cooling chemicals to keep the temperature caused by friction down to almost none.
So surface temp is not a factor in the milling process.

 

The EDM wire cut would be plenty accurate if it is set up properly, its just a slow and relativly expensive process.

 

Have I ever seen it done? I have been in the room at Mazda Hq where rotors are machined from the blank castings..
The temperature of the machining process doesn mean jackshit, the factory hardening of the rotor slot is .5 mm deep on either side of the slot, so basically when you cut a rotor to 3mm , and you take out that 1mm, you exactly remove the factory hardening, which by the way is not a heat hardening process contrary to what many people think, its a chemical hardening. Max

 

The trick is the setup, the machine that cuts the original grooves, measures each groove location from the other grooves while its cutting . Not only that it references itself from a master set of measurements from a master rotor to ensure each seal is exactly where it should be, then the corner seal pockets are centred on the fresh seal slot. If the slot if is recut again, the chances of each slot then being centred is greatly diminished. The chances of the seal being centre on the corner seal after remilling is pretty slim..
I have a set of 3mm rotors here, where not one slot is in the right place, and every non fcotyr 3mm rotor I have ever seen has been the same way..