which of these apex seals to use?
 

My apologies if this seems like a dumb question, but I am not sure which apex seals to use in my S5. A couple of weeks ago, I bought a "rebuilt" S5 and brought it home, hoping to drop it into the GSL-SE I'm building. Then I noticed the housings didn't quite match, and some research told me I had an S4 rear housing, so I decided to pull it apart and use the rear housing off another S5 with a bad front rotor.

When I cracked the engine open, I checked the apex seals, which obviously had not been replaced in the "rebuild". An example is on the right in the first picture, and in the second picture, from the top. The other, larger seal is one I bought off e-bay, used (grab-bag, cheap).

So I am hoping someone will explain, first why there are two sizes here (I can't find any reason for it on the web or this site -- and no, that's not part of a 3-piece; look closely).

Secondly, which one I should be using (I don't trust the judgment of the p.o.), the larger or smaller type.

Thirdly, is that smaller seal is still useful. As you can see in the second picture, it is not smooth and shiny, but has rough dark areas that you can feel if you run your fingernail across it, though none of them could catch your nail.

I appreciate any advice you all can give.

http://i575.photobucket.com/albums/s...en/apex003.jpg
http://i575.photobucket.com/albums/s...en/apex005.jpg

I believe that to be an RX-8 Renesis apex seal?

Are all your seals like this, or just one? It may be that they tried using Renesis rotors (higher compression) in this motor. This is not a good idea though as the Renesis seals are not designed for peripheral exhaust ports.

So the smaller one is an RX-8 seal? That would make some sense -- the p.o. had used RX-8 injectors and spark plugs, thinking they could get more power. I wonder if I have RX-8 rotors; when I hold a straight-edge across the dished area, it almost touches the bottom of the dish; when I do that on the trashed S5 rotors, there's a significant gap.

All the seals match this one, in size and condition.

Okay, wow. A little more research in that direction, and I see you hit the nail on the head:
http://www.rebuildingrotaryengines.c...renesis-rotors

Not only that, but they need to be machined to accept earlier apex seals to work right:
http://books.google.com/books?id=rhc...n%20s5&f=false

So now I know what I need to do: I need to get rid of these Renesis rotors and get a couple of S5's for my S5 engine!

You are right. They would need to be machined to accept older style seals.

As you stated, you could ditche the rotors for some s5 ones. Just check to see which counterweights/e-shaft were used. The renesis e-shaft shouldn't make a difference really as its rotation is fairly small, but the counterweights should be swapped to s5 as the different weights may cause vibration/uneven wear.

Or, if everything is already rx-8 and in good condition, you could get the rotors machined, money permitting.

Either way though, I'd try to get some money back from this guy cause you got hosed :nod: