No issues with some items that crossover when there's a significant price difference. I'd resent being bent over for a FD e-shaft if the 8 shaft is available, works and much cheaper. And everything I've read indicates it does.
But rear main seal is different. Neither are expensive and the job isn't fun the first time, let alone the second.
My guess is that while the 8 seal WILL work, you have to be careful so it doesn't walk further in as the flywheel is inserted. Since it's narrower and less contact with the wall of the stat gear base, there's less resistance and it gets recessed during installation.

 

Here's what I found when I took off my flywheel and counterweight. The seal had pushed out and became cocked and rubbed through.

 

Crankcase pressure pushing it out? Do you have the oil neck nipple capped off?

 

it's routed to a vented catch can. It was installed flush so obviously pressure behind it, maybe the vent is not sufficient size? Either way I wonder if the rx7 seal would have held being almost twice the depth of the rx8 seal

 

Damn, that's nuts!!

 

Hello all,
Apoligies for bringing up an old thread, but I have a theory.

My "rx8" main seal started backing it self out of the rear stat gear and got chewed against the rear counter weight hardware (bolts). The pics are in a link below. They look just like island fd's. This is because we both have light weight flywheels with A/T counter weights. The stock flywheel does not have any bolts that will "destroy" the seal, but will have enough room to back out and start leaking around the outer diameter of the seal. I think that when a lot of people or garages go to replace the seal with the stock flywheel, they didn't realize the seal started coming out in the first place, because the stock flywheel has a smooth surface to hit vs. the bolts on my A/T counter weight. They dont think about Atkins being the problem by giving out incorrect parts, so they go and replace the seal again! Another rx8 seal? If they didnt think about it or know that they were receiving the incorrect part, they'll just use another rx8 seal.

This was never an installation error and ALWAYS a parts error. I mean, who is able to pull an engine out, yet install a seal wrong. Doesn't sound right to me.

PS. My dads friend had a 1st gen rx7, and he spoke highly of Atkins. After some discussion, he told me that he once replaced the rear main seal himself, and shortly after, his motor seized. This was in the middle of my investigation on my rear main seal leak. Being my first rebuild ever on anything, it freaked the living **** outta me. But after some investigation, I found Atkins sells 69-11 rear main seals as ALL rx8 parts... I bet I know what happened with him, Atikns.


https://www.dropbox.com/sh/ijljapg63...MbmrAXIPa?dl=0

 

I used the RX8 seal on my old rotary engine and never had a problem with it leaking or backing out. I put around 5k miles on it.

 

^I don't think *all* the RX-8 seals cause issues in an FD application, but seems to be enough that it's an issue, especially when the correct FD part works pretty much 100 out of 100 times. Consider yourself lucky

 

^ mine was a tii engine anyways. So I can't attest to the rew.

 

how often do people use black silicone or alike around the outer diameter? That might help explain some rx8 seals being useful. The point would be that NO FD owners like to cut corners.

 

i also have never had any issue with the RX8 seals in RX7 applications. i however have seen plenty of RX7 OEM seals in the rear stat gear spinning with a virtual light touch of the fingers. the seals themselves are a poor design, which is why i use loctite or silicone to help keep them in place. as well with the RX8 seal you can't install it flush, you need to pound it in until it bottoms out, so i suspect some issue people may have with the rx8 seals is actually just faulty installation, not faulty seals.

though something else disturbs me about that last picture in this thread, the outer seal ridge is warping like due to a foreign material in the oil that is causing the rubber to break down.

but i still have a hard time believing that the seal is backing out without positive crankcase pressure, worst case the seals normally do that i find is that they simply spin in their seal bore. recheck your crankcase ventilations, whether you think it is adequate or not.

 

^Ben, were the loose seals in FD builds? I've pounded in probably.... I don't know, over a hundred of them in FD builds and they always go in firmly and definitely need some work to get seated. Never seen them go in loosely, which would have made me concerned for sure.

 

im not referring to installations, i'm talking about engines i had sitting around or pulled from cars for rebuilds so the seals usually had a decent amount of miles on them by then.

even though they spun rather easily there is still a lip at the base of the seal and a detent in the stat gear that holds them in place to prevent them from just popping out like this. however those loose seals also were leaking plenty good too.

i have tons of rear stat gears in storage, i bet almost half of them i could spin the seals in with a couple fingers and not a ton of pressure.

 

Since someone decided to bump this thread I thought I'd chime in with some new info. Over the past few months I've had a few cars develop rear main seal leaks after a few thousand miles. I have had them leak with fd rear main seals, rx8 rear main seals, oem stationary gear orings, aftermarket stationary gear orings, and basically every combination you can think of. None of the seals felt overly loose. We began applying silicone rtv to the stationary gear flange as an extra layer of insurance. (Mazda doesn't call for it and we've never needed it before) What I noticed was that they all seemed to happen on cars where the stock flywheel or aftermarket counterweight was reused. What I have found is a lot of these flywheels or counterweights developed a wear pattern where the seal rides. When putting the motor back together or changing the flywheel/counterweigh with a used piece the seal may sit on a different part and therefore leak. When you do a rear main seal or flywheel make sure there isn't any visible wear from where the rear main seal lip rides. If there is minor wear you can clean it up with emery paper using a cross-hatch pattern. Anything significant will have to be turned down or better yet the flywheel replaced. As always make sure to use rtv on the base of the flywheel nut. As these cars get older we notice more and more minor oddities pop up.

 

 

Properly installed RX-8 Rear main seal.


Typical wear on a FD flywheel



FD vs. RX8







Flywheel OD

 

not sure what that proves, the rx8 flywheel seal surface dimensions are likely the same. granted i haven't actually checked.

 

With just the knowledge I have working on cars, I would have never thought about pushing in the RX8 seal until it bottoms out. Ive done lots of rear mains and have always flushed them out. Now that I see the picture of the two seals side by side it makes sense. When I did my TII rear main, I accidentally hit it in too far (what i though was too far) and sort of freaked. Thats probably what saved mine from backing out and/or leaking. I'd have to agree that this could very well be an installation issue.

Has anyone measured the difference in ODs of the two seals? I mean, theoretically they should be the same.

 

Here you go.

 

^ It doesnt get closer that that.

Do you think a tenth of an inch on the ID could mean the difference between it leaking or not if it were to fall into the same groove?

 

the RX8 slinger ribs are also a more aggressive design than the old RX7 seals. granted i never did get into nearly as many RX8 engines as i did the RX7s, but i didn't notice the RX8s leaking nearly as often. but age could also be a major contributor in that as well.