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.

[RETed]

Originally Posted by JustJeff

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?

Oh boy, this is going to open a big can of worms...

I've always advocated the use of Mazda OEM apex seals for anything under 500hp.
They are proven, and other, superior options like "ceramics" are significantly more costly.
I've done a lot of motors with the Mazda OEM apex seals, so I know what they can and cannot do.

Several years ago, they was a proliferation of aftermarket apex seals all touting all kinds of benefits.
Remember Hurley Engineering? Crap. Seals tend to obliterate when pushed moderately. Some people claim these seals did not score housings when they let go, so this was a plus??? *ROLL EYES* You still need to rebuild the motors when seals let go.
Rotary Aviation? I dunno what generation they were on, but the early versions all had problems. Some were too soft. Some were too hard. I've had customer cars who had badly eaten rotor housings prematurely cause of RA seals that were too hard.
(I only kept track of these aftermarket apex seals until about 5 years ago, so some of this info might be outdated.)
It looks like the RA is a little better, but previous experience has left a bad taste in my mouth.
Atkins? Relatively new, but consensus was that you could not use them over 15psi. WTF? I don't like have boost limitations on my motors like that. The relatively low boost level implies these seals are on the softer side.

What I do know as fact...
We sent the Mazda OEM apex seals out for hardness testing, and results were...interesting.
Mazda has long said that their apex seals are electron beam hardened on the leading edge (the edge that contacts the rotor housing).
We found this out to be true.
The leading edge measure to approximately 60C Brinnell hardness.
The "back" side of the apex seal measure to approximately 40C Brinnell hardness.
This expensive treatment of the apex seals were not being done to most of the aftermarket apex seals out there - most aftermarket apex seals were of homogeneous hardness throughout the entire seal.
What does this expensive treatment by Mazda accomplish?
Two things...
1) The leading edge which is exposed to the most abuse (contact with rotor housing and exposure to combustion gases) is more resistant to wear & tear.
2) The back side of the apex seal that sits in the rotor is softer so it doesn't pound the apex seal springs and the rotor groove.
Yes, some of the harder aftermarket apex seals were causing excessive clearances in the rotor apex seal groove over time.
Excessive clearances will cause excessive combustion gas blow-by and, in extreme cases, contact of the rotor apex tips with the rotor housings.

I've had this information posted on my web site for years now:
http://fc3spro.com/TECH/MODS/ENGINE/...OTORS/apex.htm

I don't have any experience with any of the more expensive options like NRS, Ianetti, or any of those "cermamics".
All of these options are significantly most costly than the Mazda OEM apex seals at around $500 for a set of 6.

Back to the original question...
I set my standard for apex seals with the Mazda OEM units.
Most of the affordable aftermarket apex seals I don't consider equivalent to the Mazda OEM stuff.
Most of the more expensive stuff (which I have zero experience with) is probably better than the Mazda OEM units due to their sheer price tag.


-Ted