factory matched rotating assembly, both "E" weight rotors. i think i forgot to mark front and rear or it came off during cleaning. is it cool to just put them in however? do they have some kind of mark for front/rear on them?

i'd try and find some marks myself, but i'm not out where my parts are.

 

Kinda hard to explain but the rotors do have a front leading "LIP" edge that is very small and you can feel it where the apex seal goes. Take your finger and run accross the rotor face up to the edge where the apex seal would go. If you feel a small ridge, that's the trailing edge. You will notice the same thing on the other rotor except the stationary gear will be on the opposite side. Now place both rotors side by side with both trailing edges on top and facing you. Position the rotors so that one of the stationary gears is on the left and the other on the right. The left rotor will be your front rotor.

This trailing edge is like a scraper to help move the cumbusted fuel/air mixer away from the trailing apex seal. During assembly this edge should be on top when the rotor is on a compression stage. Hope that helps.

 

thanks, that does help. i didn't even think of that, though i've noticed those ridges before. i always assumed they were somehow a product of wear... either way, they are an indication of rotating direction.

 

I edited my post to better explain.

 

wait, that would make the lip the leading edge... and you're saying there's only one lip per rotor?

i thought each apex groove has a lip and it is the edge behind the apex (trailing).

so, the right rotor would be the front one... right? it's a weird conceptual problem

 

Are you saying new rotors have this trailing edge? I have not observed this.

 

t-von, have you lead me astray?!? i've got to send the rotor housings to JHB performance first anyways... and i have to sell my toyota before i can do that, lol.

 

The small lip is on all the rotor faces (3 on each one). I have not lead you astray. Some rotors are more noticeable than others due to the machining process. The lip would be in front of the apex seal. If both rotors are in front of you like I said earlier, you would feel the lip on top in front of the apex seal groove. That's the trailing edge. I will take a pic with my sisters camera when I get a chance.

 

It's too hard to see. You need to feel for it. Not everyone knows about this fact. I have 3 89-91 NA 9.7 compression rotors sitting on my desk waiting to go into my 20b and they have them. The 9.0 rotors that originally came out of my 20b engine (which is exactly the same as Fd rotors) also had the lips.

 

All 13b rotors are interchangable front to rear. Only the 12a had different front and rear rotors. The only time I've seen a "lip"( i'd call it a burr) on the seal groove, is when the groove has "v"ed out from high mileage.

 

Exactly, and this is the point I was getting at. You can interchange new rotors front / rear whatever except for the old 12a's. There is no lip in the machining process, and it just doesn't make sense if you understand mazda's machining process anyway. Same as Gadd the only time I have observed this lip - more like a burr on the trailing face of used rotors. It is a handy trick for identifying the front / rear rotor if you are reusing them and got them mixed up, but I wouldn't trust it because quite often the burr is on both sides. If you are really stuck, you can just replace the old rotor bearings and then rotor font / rear is not an issue.

 

They are the same PN# for what it is worth.

 

It doesn't really matter.
It's not that important that you keep them front versus rear.


-Ted