the 2 rotors i have are a little different. one has an "a" stamp the other has a "c"
was that common to have that difference in a factory built motor?
one rotor is smooth and the other has lines in the metal on the rotor faces.

 

S5 rotors will be machined (have stripped lined in the chamber)
S4 will be smooth (no lines)

 

never noticed that
i was gonna say weigh them

 

Weigh them on a scale.


-Ted

 

Going back to what Midwest first said about his rotors, one being smooth and the other with "grooves", I have seen the same thing. When I took my '89 NA apart, one rotor looked like it was rough machined and didn't go through a finishing process. From what i could tell, it appeared the "rough" one was ever so slightly smaller than the "smooth" one. Maybe .005" per side max. I would like to know if anyone else has seen this. Didn't meen to highjack, but, I posted this question before and got no reply. I'm very curious about this.

 

S4 rotors pits look casted and S5 look forged

 

I would really like to get an answer on this. To be specific, the face of the one rotor (outside the combustion chamber), had linear grooves much like the grooves IN the combustion chamber. All the combustion chambers on both rotors looked the same; rough with toolmarks running the length of the chamber. I am a machinist. I believe the surface of the smooth rotor is ground. Correct me if this is not standard Mazda practice. I believe Mazda may have let a few roughed-out rotors, slightly below spec, to continue into production. Has anybody seen this same thing?

 

i've seen series 5 rotors have machined-looking lines in the pockets and be smooth looking

series 4 always have a cast look

 

Go find the reply by Rotary Resurrection - he's torn down more engines that I have, and his experience is that there is no consistent pattern on what rotors are machined.

I used to think that S4 were all cast face, and S5 were all machined face, but I trust Rotary Resurrection's experience.


-Ted

 

All S5 rotors have a machined combustion depression. All S4s have a cast combustion depression. The difference is obvious. Some S5 rotors have a tooled side outside of the combustion depression while others are entirely smooth. I just rebuilt an S5 NA engine this weekend that had one tooled rotor and one smooth. Again the difference is obvious but they're both S5 rotors with a tooled combustion depression.

 

I think C.Ludwig is with me. I was talking about the area outside the combustion chamber. One was smooth after cleaning , and the other was rough. I placed the one over the other and it seemed slightly smaller than the other by feel and a straight-edge. The rough one was the front rotor. I wish I could send you pics but I polished it to make it look like the other. (?)! I edited to confirm this was a '89 NA Auto. I am very confident it is the stock motor.