Is this rotor usable?

[JustJeff]

I bought this and cleaned it up and found what the pics show. Opinions are greatly appreciated





This is my old rotor that I detonated, it seems like it could be in better shape than the one I bought

[JustJeff]

Seller is replacing the rotor

[rxspeed7]

Good cause I'm pretty sure that is far past the .006" spec for rotor groove clearance.


Zack

[TitaniumTT]

Yeah, that's FUBAR

[JustJeff]

Thanks you guys confirmed what I didn't want to deal with. But the seller is giving me no problems with getting me a replacement.

[rxspeed7]

That's good man. Usually when you cant see a noticeable gap there no good.


Zack

[RETed]

I see no problem using it if clearances are okay, and you're not building a "spec" motor.
You're going to lose a little bit of compression (should be way under 10%, more like 1%), so I doubt you'd feel it (maybe a couple of HP).

The rotor face is machined, so is this a turbo or non-turbo rotor - 9.7 or 9.0?


-Ted

[JustJeff]

Originally Posted by RETed

I see no problem using it if clearances are okay, and you're not building a "spec" motor.
You're going to lose a little bit of compression (should be way under 10%, more like 1%), so I doubt you'd feel it (maybe a couple of HP).

The rotor face is machined, so is this a turbo or non-turbo rotor - 9.7 or 9.0?


-Ted

It's an 9.0 FD rotor I was going to use it for a S5 13B turbo rebuild. I had considered swapping it into the other housing so that the momentum of the engine would always be pushing the apex seal away from the gap.

I sent the seller a PM with the same pic and he said he'd replace it soon as I got it back to him.

[RETed]

Small cavaet when using FD rotors in an FC 13BT engine...

The FD rotor bearings are different.
I dunno if it's a big deal to you, but the FD rotor bearing groove is deeper than the Kouki FC 13BT rotor bearings.
Also, I think Mazda has like a bazillion different rotor bearing sizes / part numbers for the FD rotor bearing.
The FC3S 13BT rotor bearing only has two - "normal" and "oversized".

Although this should not matter too much for a street motor, but if you're going for big power and or spin over stock redline, this miniscule fact might come into play.

Glad to hear the seller is willing to take care of the problem without much fuss...


-Ted

[JustJeff]

Originally Posted by RETed

Small cavaet when using FD rotors in an FC 13BT engine...

The FD rotor bearings are different.
I dunno if it's a big deal to you, but the FD rotor bearing groove is deeper than the Kouki FC 13BT rotor bearings.
Also, I think Mazda has like a bazillion different rotor bearing sizes / part numbers for the FD rotor bearing.
The FC3S 13BT rotor bearing only has two - "normal" and "oversized".

Although this should not matter too much for a street motor, but if you're going for big power and or spin over stock redline, this miniscule fact might come into play.

Glad to hear the seller is willing to take care of the problem without much fuss...


-Ted

Thanks Ted, I did not know the bearings were different between the rotors. Though it won't be used for a high HP or RPM engine.

I'm curious on how that damage and gap will effect the actual apex seal. I hadn't considered that it would create compression issues. I had assumed it would effect the apex seals longevity/lifespan. My assumption was that the gap would cause the seal to bend and break...essentially cracking the new seal where the old one detonated. I'd have to think it would be more prone to breaking under detonation on that same spot?

[NoDOHC]

Usability is in the eye of the beholder. If I had the rotor in my hand and I wanted to put an engine together that weekend, I would take a hammer and tap the face of the rotor about 1/8" away from the groove in the place where it was too wide until it was the right width all the way down, then I would use it.

I have done this numerous times with no ill effects at all. A friend who builds more rotaries than I do told me that I could do it, so I gave it a try with great success.

If you are not confident of your machining (or open-die forging) talent, then get a different rotor (as I see you already have).

[RETed]

I've seen worse off rotors than that used in turbo 13B's with no significant problems.

Personally, I wouldn't hesitate to use that rotor (although I'm more of a 8.5:1 junkie ) in my engine - take it however you want and standard disclaimers apply here.

Good parts are just getting harder and harder to come by.
The FD is already hitting 15 years old since last production ran.
You tend to get a little looser in your standards when parts start to get harder and harder to find.

The apex seal should have enough support as long as it passes clearances spec.
The apex seal is ductile enough to handle most "normal" combustion loads.
400hp should not be a problem, as long as tuning, fuel, and ignition timing are spot on.
This is assuming at the very least Mazda OEM 2-piece apex seals or better.
Once the motor detonates, all bets are off - you might be a little bit more safety margin from a rotor with better grooves, but IMO it's not that much more than most people think.


-Ted

[JustJeff]

Originally Posted by NoDOHC

Usability is in the eye of the beholder. If I had the rotor in my hand and I wanted to put an engine together that weekend, I would take a hammer and tap the face of the rotor about 1/8" away from the groove in the place where it was too wide until it was the right width all the way down, then I would use it.

I have done this numerous times with no ill effects at all. A friend who builds more rotaries than I do told me that I could do it, so I gave it a try with great success.

If you are not confident of your machining (or open-die forging) talent, then get a different rotor (as I see you already have).

I'm a little confused but think I'm understanding you. You are saying go 1/8" from the groove and tap it back in?

This is my first rebuild and extensive engine work. I've always been a perfectionist and loose sleep over tiny details. As long as I'm understanding what needs done I'm confident I could get it right...but the idea of taking a hammer to engine parts does seem counterproductive

Originally Posted by RETed

I've seen worse off rotors than that used in turbo 13B's with no significant problems.

Personally, I wouldn't hesitate to use that rotor (although I'm more of a 8.5:1 junkie ) in my engine - take it however you want and standard disclaimers apply here.

Good parts are just getting harder and harder to come by.
The FD is already hitting 15 years old since last production ran.
You tend to get a little looser in your standards when parts start to get harder and harder to find.

The apex seal should have enough support as long as it passes clearances spec.
The apex seal is ductile enough to handle most "normal" combustion loads.
400hp should not be a problem, as long as tuning, fuel, and ignition timing are spot on.
This is assuming at the very least Mazda OEM 2-piece apex seals or better.
Once the motor detonates, all bets are off - you might be a little bit more safety margin from a rotor with better grooves, but IMO it's not that much more than most people think.


-Ted

That's an excellent point about the age of parts we are talking about. I had considered that exact thing. Maybe the one I get won't be any better or have other issues the one I have now doesn't have.

I checked clearance on my original rotor. IIRC the difference from the good corner of the apex groove to the bad was like .002 to .003. All I did to test was put corner seals and plugs in with apex seals. First found the feeler that fit the bad corner and slid it towards the good. Then compared that to what I could slid on the good corner.

I did the same for the rotor I bought but for the life of me I can't remember the numbers and didn't write them down. It was better than my old one. I had been planning on checking it again before sending it back. I'll report back once I have those figures.

[JustJeff]

Originally Posted by RETed

This is assuming at the very least Mazda OEM 2-piece apex seals or better.

I'm a lil confused by the context of this statement. You saying OEM or better apex are good for 400hp. Or that OEM or better in relation to my damaged rotor?

In giving advice about the rotor keep in mind that I'll be using either RA classics or Atkins apex seals. Right now I'm leaning towards RA simply because I've talked to some guys running turbo setups that have been happy with them.

I know OEM are the best choice of the three, but money is an issue. Following the logic I'm going to assume that because I'm not using OEM that adds an extra variable/risk, possibly making the damaged rotor a larger factor? Did I follow that through correctly?

Ted, I thought of something rebuild related, but unrelated to this thread. I'm gonna toss you a PM.

[TitaniumTT]

This is all good info, so post it up as opposed to PM's

As far as the rotors... my feelings, it's obviously damaged, gases are going to get in there and do things that it shouldn't do. The pressures can force the apex seal/corner seal harder into the sealing surfaces than they should and cause accelerated wear... I know someone who tried this by milling gas ports into the rotors. Killed the housings in about 5k from what I understand.

That little imperfection could lead to the seal moving back and forth and wear improperly. Also thinking carbon buildup is going to increase in that area as well.

Regarding the seals... I'm running the RA super seals. When the fuel filter clogged she ran 13.5-13.7 AFR's and 15+psi and detonated for sure. The seals didn't crack, they didn't chip, but they did warp. IMO they saved the engine though.