I'm in the process of my first rebuild. I've finished the brunt of the cleaning on the rotors, and at first glance they look good but I am mildly concerned. From what I've seen there doesn't seem to be anything fatal, but I do have a few questions just to be safe.

The front rotor (right) seems to have a smaller compression dimple than the rear rotor (left). I've heard that S5 and S4 have different compression ratios, but i'm not sure if this is a different rotor or just manufacturing variations.

The front rotor also seems to have vertical streaks or grooves running down the face. This is present on all faces and I am unsure once again if this is manufacturing or damage? The housings don't have any damage so I am leaning towards the former.
Below is the streaks on the front rotor (top) compared to the smoother rear rotor (bottom)



Finally, the rear rotor does seem to have small defects in on the edges of the apex seal grooves. This also does not seem to be any damage through use, but I'm trying to be diligent and as I'm new I decided to make sure.



Sorry for low quality images. To me looking at the rotors, it looks inconsequential especially since I have very modest N/A power goals. There is nothing jutting into the apex seal groove, just small nicks on the outside. The rest of the rotors are essentially pristine. I haven't tested tolerance yet as my feeler gauge isn't as accurate as possible, so I'll be buying a new one and continuing with that process, just wondering if there are any visual concerns.

Anyone let me know if there are questions, and thank you so much for your help!

I also seem to keep getting logged out of this website in the middle of drafting this post, just curious if that's a me issue or a website issue.

 

EDIT -
actually, hold off on what i said. the shape of the recess (combustion chamber) on the one i said is S5 or later is off. the recess definitely looks S4, so maybe some of the S4 rotors were machined like that and i did not know. sorry.

it looks like you have rotors from both S4 and S5+. the front (the machined one/grooved) is S5+, while the rear (the smooth one) is S4. i do not know how to tell (from a photo) if the S5+ one you have is from an N/A car or Turbo though. either way, you are going to have to choose one and find a match for it because the compression ratings on them are going to be different if you mix Series.

 

So the rotors should be a match? Just wondering if I have anything to worry about or if I should just continue as usual.
You said you can't tell from a photo, if there's any doubt then what methods could I use to determine it? (Tried searching for rotor differences, couldn't find a thread)
Thank you again

 

13B rotors should match in terms of Series and compression. those criteria are pretty absolute. you don't want to go mixing them up when it comes to those things because they got progressively lighter with each series and, most times, compression ratio changed as well. i suppose, if you have a scale that is accurate enough (to one or two places), then you could weigh the ones you have and see what's what.

Mazdatrix rotor chart: https://mazdatrix.com/rotor-weight-a...ression-chart/

for compression ratio, you can probably check the recess with water, but i don't the value for S4 rotors and the Mazdatrix chart only references S4 Turbo and S5 N/A rotors by volume.

as i thought i understood it, starting with S5 the rotors were machined from the factory, and so they had those lines in them. however, as i said, i've never seen an S5 or newer rotor with a recess that looked like your photo. that looks like an S4 recess, so apparently i missed some detail over the years.

 

I may take them in to mazdatrix and see if they'll help me, as my scale is only accurate to the pound. Thank you!

 

when they figure it out, please post back here. i am definitely curious, too.

 

It's a mid-series manufacturing changeup, but also since the tub looks different double check that one isn't stamped 'T' in the rough casting next to the non-gear side of the bearing. If they're the same weight, take 2mm apex seals, and .7 (or whatever it is, I'm blanking) side seals they're interchangable.

I've built personal engines with them, I haven't been asked to build 'heavy' NA rotor engines for quite some time.

 

those grooves are from manufacturing, it needed a new bit in the machine

 

you are correct! 0.7mm.

 

I tested them at home but my method did lose a little bit of water.
The grooved rotor tested 27cc of water
The non-grooved rotor tested 29cc of water. I also noticed upon very close look that there are 5 little grooved lines very close to the tub, So i'm concluding they're both machined. I also checked for a T and did not see one. Still very confused.
I expect that I could've lost 1-2cc of water, so the difference isnt conclusive enough for me to make a decision.
From the chart, 27 doesnt seem possible for an S4 and I am absolutely positive that I couldn't fit any more water in the recess. Aus Rotary forums has a post stating that some S5 rotors still had a cast compression dip, not sure whether that is true.

I'll move on to measuring the weight.

 

the S5 rotors have a machined combustion recess. the cast rotors had a variance of like 0.3 compression ratio, and the machined, S5 and up are something like 0.03.
so the S4 rotors are 9.4:1 compression, but its +/-0.3, the S5 are 9.7:1, but its +/-0.03 or whatever it is. there is an SAE paper on the updates for 89.

also they made these rotors from 1985-up to like 2018 or so. its possible that a rotor from 1985 and a rotor from like 2010 aren't going to be identical

 

Awesome, learning the tolerance answers all my questions so thank you so much.

Rotors were within 50 grams of eachother, definitely S4.
I'd guess these rotors are both the original from the engine. (it's hard working on a car with no history).

Looks like I should be all good to go. Hope this thread helps some-one eventually.