rotor/housing damage
 

After taking her S5 T2 for a short, low speed ride, my daughters car lost all compression in the rear housing and we had to tow it home.
I disassembled the rear housing today and this is what I found.
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Looks like a corner seal impression on the rotor, right? How did a corner seal pop out of its original location? What would cause that to happen?
Looks like I'll need a rotor and a housing. The iron looks pretty good.

Could also be a small nut that may have fallen into the intake manifold...

Thanks for the input.

I think the engine has about 400-500 miles on it since the drebuild. i guess the corner seal might have fallen out while setting the rotor in place but the seal must have been hiding out someplace until now.

Sorry for your damaged engine. I may seem like captain obvious, but additional facts would clarify things. Were any corner seals missing from that rotor? Did the apex seals survive or was 1 or 2 of them fragged??

Was the engine ported? The corner seal would have had to fall into the intake port and then get ingested by the next intake event.

When I first posted I didn't realize that 1 corner seal was missing. All 3 apex seals are intact although the one next to the indentations is pinched in place. If there are no marks on it wonder if it can be reused.

K-tune may have nailed it. Can you post a close-up pic of the intake port and perhaps set a corner seal on the outside for scale. Looks like you may have overcut the port outer edge enough to lose corner seal support. Hate to say it, but if so, that rear iron is scrap.

It's not worth it, buy a new apex seal. The old one died with the rotor.

If it was running fine for 400-500 miles the corner seal wasn't hiding anywhere. My guess is that it just slipped out due to porting too close.

I will get a pic when I get home later today but I didn't do the porting myself. I shipped the end irons out to Las Vegas. The guy that ported the iron owns a shop where he specializes in RX7s.
I finished taking the engine apart and I never did find the missing corner seal.

Did you check inside the turbocharger? It would have had to make it through the turbine wheel, and I don't think a corner seal will fit through there without causing damage.

Whoa, you mean the corner seals are breeding? Sweet.:egrin:

Here is the pic of the intake port with a corner seal.
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I don't get it.

i dont like the trailing edge of that intake port close to the water seal very much. Put a housing on it to see exactly how much distance is left between the port and the housing. I know, more pics haha

Looking at the seal wear track on the face of the iron, it looks close. Others on the forum with more porting experience than I could be more definitive, but I'd be willing to bet a lot that the upper corner of the secondary port swallowed the seal under spring pressure.
Get another opinion prior to junking the aft iron.

Thanks, I appreciate your input. I won't be home for a few days but when I get home I'll get the pics.

i would tend to assume the corner seal fell into the intake port during engine assembly and then was ingested into the engine after a slight bump. there's no way it came out of the rotor, went into the intake and then got sucked into the engine after it was assembled. at least half of the corner seal rides on the exposed intake port. the replacement iron was port matched to a previous port job but they did were not large enough to cause a corner seal to be fully exposed, although they were slightly larger than my template i saw no problems with interference.

talk about bad luck followed by bad luck.

the housing is junk, the rotor is probably salvagable but i wouldn't expect to set any horsepower records with it since the compression face is partially weakened now(for a stock turbo car it should work just fine). the seal slot could be cleaned up with a file to prevent a new seal from pinching. that one face will probably be a few psi lower than the others but still within factory specs for differential pressures, it would still idle perfect and you wouldn't even notice a difference in power output or longevity.

That's not from a corner seal.

For one, a corner seal is a mighty big piece (relatively) to lose during assembly and not notice or hear. An apex spring, sure, but a corner seal...that would be hard to do.

Next, without the corner seal, you'd have no corner seal spring there either.

Also, if it were a corner seal that magically dropped into the chamber while running, it would have gotten smashed in half and broken at the weakest point (the bottom), and would not have made a sideways perfect impression.

Something as round and large as corner seal laying in the intake tract would have gotten sucked down within minutes of startup, not weeks and hundreds of miles. IT's round, after all, and the airflow would have "rolled" it right into the chamber very quickly.

Finally, and most obviously, if you had no corner seal, then a side seal and spring would have slid very far out of place, and the seal would probably have snapped off/worn at the ends badly. You would have had VERY poor compression on two of the 3 faces in that chamber from the very first second you fired the engine. It would have run like a 6 cylinder running on 3 or 4 cylinders.

So for these reasons, I suggest that it could not have been a corner seal dropped during assembly.

Now you're thinking, the porting is too big and the corner seal fell out while running. Again I say this is not possible, at least not unless you botch the porting by about 10mm which would be kind of hard to do.

So for these reasons, I say that it is not a corner seal's fault. I'd say it is a random washer or small nut that caused it. I've seen this a few times before. I had a guy who bought a car that I had built, the car had a rebuilt engine, and he was dicking around with the intake off it afterward. Then it would no longer run correctly and he pulled it and sent it back to me. The impression looked exactly like what you've shown there, and it did exactly what you describe to the rotor apex seals. I eventually took the turbocharger apart and found a flat washer, folded in half, neatly tucked into the internal scroll of the turbine housing.

He already said that upon disassembly a corner seal was missing.. Don't know how it fell out, but that's definitely the problem.

to be honest, i lose all sorts of springs and seals while disassembling engines no matter how careful i am. it's easy to look away for a split second and corner seal has dropped into a coolant passage or rolled under a bench never to be seen again. disassembling is dry so the seals fall out extremely easily. if the corner seal spring was there i also agree it was probably initially there but got lost during disassembly.

initially i thought it was a washer also but it does seem to have a "C" impression like the corner seal although i also agree that it is probably too thick to make it through there sideways. the compression pocket narrows down to only a few mm at TDC, not enough space for a corner seal to make it through, a thick washer however would be just about right, such as a lockwasher which may also give a "C" impression.

you can still see the corner seal wear track covering at least 6mm of the iron so there is no way it made it into the intake through the port after assembly.

it wouldn't be the first time i saw a nut/washer sitting in the upper intake that took a couple of hours to work its way into the engine.

tape up all exposed open ports until assembling that portion of the engine.

if you want to be positive measure the exposed lip of a corner seal and then measure the impression thickness on the rotor or simply put a corner seal onto that impression and i have a feeling the shape is going to be much larger than the corner seal. most likely an exhaust lock washer or front cover bolt lockwasher will be a positive match. sometimes it pays to take a little longer and be patient, ripping through an engine in a hurry usually causes issues like this to arise.

the mystery continues
 

Actually I agree with this. At first glance it appeared to be the right shape, but upon closer inspection, that is not the impression a corner seal, nor spring would make. The odd thing is that while the c-shaped impression could be a lock washer, the disk shaped impression is not a washer. Then what is it??

Anyhow, the important thing is that your iron is OK to reuse.

Thanks for the input guys. I just got back from vacation.
I took a couple of pics of the housing installed on the iron with a couple of corner seals set in place. It looks like the corner seal extends into the port opening by only a millimeter or 2.
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Thanks for the input guys. I just got back from vacation.
I took a couple of pics of the housing installed on the iron with a couple of corner seals set in place. It looks like the corner seal extends into the port opening by only a millimeter or 2.
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You should improve your understanding of how the corner seal tracks across the port. It doesn't ride the rotor housing wall as you've indicated. Look closely at the existing track mark on the side housing for a better idea of the epitrochoidal path traced by the apex seal.

You'll be a little scared, but fortunately the corner seal has a tight fit in the deep cylindrical counterbore of the rotor, so it need to be effectively fully unsupported before it will pop out completely.