Is this rotor usable?

[rxspeed7]

^I'm totally with you on this. If this is your last hopes for putting the motor together then by all means use it but if you can I know you'd feel better using a rotor you know for sure is good. It's the little things that will always come back and bite you in the ass.

Zack.

P.S. As for me i'm going to be rocking some atkins seals on this motor.

[JustJeff]

Originally Posted by 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.

I'll create another thread about the PM..make it easier for people to search and find.

You've got good points about added carbon build up in that spot and added wear.

About the detonation...that's what I've read and been told about RA seals. They seem to be more resistant to detonation. I won't be doing Super Seals though. It seems like most of the guys running higher HP and boost are going with the Super Seals. I'm thinking with my mostly stock rebuild and rarely hitting 12psi on my stock turbo I'll be ok with Classics.

I'm curious if you had chatter marks from the Super Seals? IIRC what I read about RA is some chatter marking with the Classics. More chatter marking with the Super Seals.

[TitaniumTT]

I would go for the Super Seals... it only takes one good knock. I would say use the classics in an N/A build, the supers in any boosted engine

Chatter Marks - I didn't have any when I tore that engine apart. I'm also running Idemitsu "fuel lube" being injected through the OMP via the RA OMP adapter and I also run .25oz/gal in the tank. If I'm going to be doing NOTHING but highway driving, I'll knock it in half.

[JustJeff]

Originally Posted by TitaniumTT

I would go for the Super Seals... it only takes one good knock. I would say use the classics in an N/A build, the supers in any boosted engine

Chatter Marks - I didn't have any when I tore that engine apart. I'm also running Idemitsu "fuel lube" being injected through the OMP via the RA OMP adapter and I also run .25oz/gal in the tank. If I'm going to be doing NOTHING but highway driving, I'll knock it in half.

Where did you put the reservoir for the RA adapter? I'm thinking of doing that mod also. I saw a right-up for an FB and the person mounted it to the passenger strut tower. On a turbo I don't think that would be the best location.

[TitaniumTT]

Where the airpump once lived on the FD..... running the REW waterpump.

[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

[RETed]

Originally Posted by TitaniumTT

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.

This is basically the primary reason to worry about clearances.
This is why I mentioned as long as the clearances should be measured.
Pics can sometimes distort dimensions, so it's always prudent to go measure everything yourself.

Side note...
There will always be a little blow-by past the seals.
Anyone who has opened up a high mileage motor (with stock OMP still intact) and checked the rotor apex seal grooves has seen the crap that gets lodged under there.
For the most part, IMO, that carbon build-up is relatively soft.
The apex seal is bouncing up and down in the groove and will most likely just mash all that carbon build-up under it until no more can fit under it.
From my experience, just swapping out the stock OMP with pre-mix greatly reduces the amount of carbon build-up in the engine.
Also, having the fuel mixtures tuned right (not excessively rich) will greatly minimize this carbon build-up also.
At the same time, it's a given that your ignition system be working in top shape to fire off the combustion charge, as misfires are just as bad as a too much fuel.


-Ted

[JustJeff]

Thanks for the posts Ted

I had read your article on apex seals several months ago. In a perfect world I'd go with Mazda seals, BUT I'm already on limited finances from all the bad economy stuff. On top of that I'm trying to get money set aside to start graduate school. I figure now is the perfect time to add some education. There isn't any hiring or moving up going on anyway. Might as well do what I can to pad my resume.

I'll certainly give apex seals some more thought. I suppose I could reuse my pressure plate rather than replace it. Use that money to offset cost between RA and Atkins compared to OEM.

My thoughts on housing wear related to apex seals is that I doubt my housings would be good for another rebuild after this one. So I wasn't as concerned about those. Though I am keeping in mind housing wear and compression.

I hadn't considered wear to the apex groove. I'd like these rotors to last beyond this rebuild.

I took some pics of clearancing my apex grooves. I'll post them up pretty soon.

[JustJeff]

OK...I don't own a dial caliper so this is what I did to compare one corner from the other. Feeler gauges stuck between the apex seal and the groove. I'm sure it's not as accurate as having a dial caliper. But what I was looking for was a comparison from the good end to the bad of the groove.

My old rotor I took to a machine shop and had them measure it. I don't remember the figures and can't find my notes ATM.

I'll be buying a dial caliper tomorrow. The seller seems to be annoyed that I had not measured. I'm annoyed for the obvious reasons.

Bad Corner


Good Corner


As a comparison the rotor in my engine when it detonated
Bad Corner


Good Corner

[TitaniumTT]

Originally Posted by RETed

This is basically the primary reason to worry about clearances.
This is why I mentioned as long as the clearances should be measured.
Pics can sometimes distort dimensions, so it's always prudent to go measure everything yourself.

Side note...
There will always be a little blow-by past the seals.
Anyone who has opened up a high mileage motor (with stock OMP still intact) and checked the rotor apex seal grooves has seen the crap that gets lodged under there.
For the most part, IMO, that carbon build-up is relatively soft.
The apex seal is bouncing up and down in the groove and will most likely just mash all that carbon build-up under it until no more can fit under it.
From my experience, just swapping out the stock OMP with pre-mix greatly reduces the amount of carbon build-up in the engine.
Also, having the fuel mixtures tuned right (not excessively rich) will greatly minimize this carbon build-up also.
At the same time, it's a given that your ignition system be working in top shape to fire off the combustion charge, as misfires are just as bad as a too much fuel.


-Ted

I agree 100% Ted, what concerns me though is that a gap like that is going to allow more gasses in there which IMHO will lead to more carbon build-up. Yes the Apex seal moving up and down is going to keep it moving freely, but bad things are more likely to happen due to carbon build up than a rotor without that imperfection. Plus you gotta wonder what happended that caused that and what else was damamged that's not being seen.

As for that carbon, fact of life... I've actually got 2 n/a motors in the shop right now that need to be torn down. One with the OMP, one without. I'll snatch a few pics and post them up. For my engine, even while running spot on (.82L under bull load, .96L cruise) and running idemitsu premix, I was surprised at how much carbon buildup there was in a short amount of time. Granted the buildup was softer and not compacted in there, but I was a little surprised. One more reason I'm going to build my FD around E85.

[RETed]

Originally Posted by TitaniumTT

I agree 100% Ted, what concerns me though is that a gap like that is going to allow more gasses in there which IMHO will lead to more carbon build-up. Yes the Apex seal moving up and down is going to keep it moving freely, but bad things are more likely to happen due to carbon build up than a rotor without that imperfection. Plus you gotta wonder what happended that caused that and what else was damamged that's not being seen.

Ever get to tear down one of those way north of 100k+ mile stock engines still running the stock OMP?
Yes, there is a LOT of carbon under there, but the springs (and seals) all look like they still have full travel (well, not measured, but just an eyeball guesstimate).
I'm talking about side seal springs that are almost welded into place due to so much carbon in the grooves, so when you do pull them out, you swear you're going to snap it into pieces.

I'd figure the premixing has got to help in this case?


-Ted

[TitaniumTT]

Originally Posted by RETed

Ever get to tear down one of those way north of 100k+ mile stock engines still running the stock OMP?
Yes, there is a LOT of carbon under there, but the springs (and seals) all look like they still have full travel (well, not measured, but just an eyeball guesstimate).
I'm talking about side seal springs that are almost welded into place due to so much carbon in the grooves, so when you do pull them out, you swear you're going to snap it into pieces.

I'd figure the premixing has got to help in this case?


-Ted

Yup, tore a few down that were north of the 200k mark with the OMP still working and dayum... so yes, I see your point. My concern is, those engines were factory fresh with very tight tolerances when they were first built using all new parts. So, with that gash in there, it's obviously going to let more in than a new rotor. Is it enough gas/carbon to make a difference? I don't know. But it is one of my concerns using that rotor.

On the side seal subject... that's exactely how I lost the first engine after the swap. It was an RE with REW housings. SWEET!!! REBUILT!!!! Comp was 105F/107R so I ran it. The thing lasted 4 hours.... yup... 4 hours before a CARBON LOCKED side seal let loose. I was upping the boost and when the combustion temps/pressures got high enough the seal wanted to move. It couldn't and broke loose wiping out the Apex seals as it went by. Bummer for sure. Upon disassembly it looked like when the engine was "rebuilt" it was just new housings/Apex seals as the carbon buildup on the side seals and oil control rings was out of control yet the exhaust, face of the rotors, were all fairly clean.

Lesson learned.... ALWAYS tear down an unknown engine. It's the only way to know for sure.

[2gslse]

I would think that apex to groove clearance is excessive I checked a set of used rotors and they were .002"-.003"

[NoDOHC]

I think that RETed is correct, that leaner mixes will protect from carbon buildup to a large extent, as will careful selection of engine oil or running premix. I get carbon buildup in my '91 driving around town (where it runs open loop and filthy rich) but it goes away after a long highway cruise (due to closed-loop, stoic fuel mix - or maybe just extended operation). My '86 (which run 16.2:1 AFR (lambda of 1.1) everywhere but WOT) never experiences the carbon-buildup-characteristic knocking that the '91 does (although this may have something to do with the 9ish 7,500 rpm shifts that it experiences everyday on the way to work). My 13,000 mile teardown (which is still a sore subject) indicated very little carbon buildup on the rotors (although they were polished).

[JustJeff]

The numbers are all
FD rotor
.080
.080
.085-.090

What I found after more measuring is that the measurement on the damage varies depending on location along the groove's damage and also how deep I take the reading. Obviously with the damage the edge of the groove angles a bit so that the top is a higher number than the same spot but a touch deeper. At it's worst I found .090. I still haven't looked in my FSM or Haynes, I got home last night and realized I had work to do for this coming work week.

I have the day off tomorrow and am planning to take the rotors to a machine shop. I bought my tool from Harbor Freight and would trust a machine shops tools more.