1991 Turbo Rx7

Alright so about a year ago I decided to rebuild my motor with some half bridge port plates, super seals apex seals, front mount intercooler, greddy e-mangae, and a few other things I can't think of at the moment, and it ran beautifully. But about a month ago it decided to poop out on me. Out of nowhere I heard a loud knocking noise as if something had come loose and was just being thrown around in the motor. Yet, the motor would still run and had full compression for all the seals.

Either way, I decided it was in the best interest to pull the motor and take a look at what lie inside. I pull the rear plate off and what I find is a shredded stationary gear and a cracked/broken rotor gear. I have some pictures below to show the damage and really all I can think of is just a mechanical failure of some sort. I have never seen this happen before. But I was wondering what you guys thought.

I have worked on rotary motors for quite a while and have and Fc and an Fb. The next step is the Fd But still I just want to know what you guys think went wrong or if you have encountered the same thing before.

Pics:




And here are pics of my cars as well, seeing as how I don't post on here much but I do read on here every now and then, I figure it would be nice for you to at least see my cars.




Also I plan on being at Zoom Fest so anyone else who is going let me know. I'm really excited for it. I couldn't make it last year but this year from what I understand will be even better.

Thanks for any help too.

 

Also I need to ask, I have NEVER reused apex seals. But these apex seals look stout still and I don't want to only get a max of 9,000 miles out of them. What do you think?

 

If the apex seals are new with little runtime on them, there is no reason not to reuse them.

As for the engine, were you over-revving it? How about oil pressure? Bearing clearances?

 

Hows the eccentric shaft in that area?

 

Never over revved it and was in first cruising to 20mph when it happened. The oil pressure did start to drop quite a bit to definitely below normal. I checked the oil and it seemed fine. That confused me but I decided since the bearings were new and maybe after just a little run time it was ok for it to drop below what it used to run at before the rebuild. Obviously figuring the motor should run smoother thus lowering the oil pressure just a bit of course.


The eccentric shaft is completely fine. It's so fine in fact, that I plan on reusing it. there seems to be nothing wrong with it, no scratches or even what could look like a rough rub mark. I do have an extra eccentric shaft but this one seems completely fine.

 

As for the apex seals, spec them out according to the FSM. There should be a warpage test, height test, and thickness test.

 

IMO that failure was probably cause by incorrect bearing clearance like Aaron mentioned.. also did you match the rotor weights correctly?

 

Yeah, the rotor weights were matched. I will say this was the first time I had put new bearings in, so it's definitely possible. But I will say the shop I did it at and the man I had help me work and build performance cars and have built several 13bt motors with no problems before. (I have only built my own, but this one was ported and I wanted to tune it, so the help was necessary.) I would have assumed that he would have noticed it, but like I said it's still very possible that is the case.

Would lack of oil to that rotor be a possible cause. One of the lines from the OPM was broken when I was looking it back over and I'm not sure if that happened while I was taking it off or if it happened while driving. It seems though, that would have caused my loss in oil pressure, and now seems that would make more sense.

 

no a broken OMP line wouldn't have caused that damage, from my knowledge you can run a motor without a omp or premix for quite a while before the seals wear out, its only there to extend life of the seals in the motor.. its also possible you didnt set your end float correctly, are you sure it was set right?

 

A friend of mine had the same thing happen, we couldnt figure out what happened. We just decided that the stationary gear broke a tooth and chewed everything up.

BTW, you should match your rotor housings when you rebuild that one.

 

Rotor housings or just rotors? I've never heard of rotor housing matching before.

 

Maybe he's talking about the porting on the housings. Rotor weight matching almost goes without saying.

It appears that the rotor gear broke near one of the pin areas (for lack of a better term?). I'm also wondering if maybe some debris made it's way between the gears? Does that happen?

 

Both, but what I was referring to is that he has mitch match "series" rotor housings. Notice the leading spark plug hole location.

 

At the time, when rebuilding the motor, I would have said I was 100 percent sure everything was done correctly. But now I will only say I'm 90 percent sure it was done perfect. When the knocking occurred, it wasn't sudden. There was a light knock that started and I had enough time to try think about what the faint noise was (couple of minutes) before it sounded like something fell out of gear and the knocking just got loud and I immediately knew it was in the engine. So I stopped immediately, did a compression test and all seals had compression. But I decided I wouldn't find the cause without pulling the motor either way. But the motor would run even with the damage. I only say all this because maybe this helps in the diagnosis. It's obviously hard to diagnose something like this. But curiosity is killing me.

Yeah that's definitely going to happen with the next rebuild. I have two other motors laying around I can pull parts from. I had never noticed that before. This is a motor I tore down and rebuilt from all the same parts (excluding seals of course.) Even in this tear down I didn't notice it. You have very good perception my friend. Thank you.

 

Did you re-seat the stationary gear when you assembled it? Did you measure rotor running clearance? There are a few variables such as I mentioned or a failing part non viable or you missed, over revving. Without wear to the bearings I wouldn't be looking at oil myself, appears to be more physical failure.

 

I didn't reseat the stationary gear, but I did measure the rotor running clearance. I agree on the physical failure part as well.

On this same thread, while I'm at it. I am going to rebuild this motor with full bridge ports now. I want to know what the life expectancy loss is on that kind of build. I also do understand to get the full performance out of that kind of porting I do need to get free flowing exhaust and a much bigger turbo and all that. I have all of it already, it has yet to be put on though. So I can be spared of that. But with stock injectors, what kind of power can I expect if I get a fuel pressure regulator instead of upping the size? Just for now, I already have a regulator and want to know what to expect?

 

wow good eye man...i never heard of mixing the two series housings but i cant see how the motor would even run right with the spark plug being in a different location..wouldn't that throw the spark/combustion out of timing? The rotors would not be combusting the same way if the plugs in a different location correct? why did mazda change the location?

 

stock injectors? is that a joke? haha

 

ok so i was doing some checking and having that rear housing as a S5 ***** up your ignition timing , so i guarantee your motor blew because of that.. that rotor was probably doing some crazy **** inside ther, you gotta figure the front rotor has a different ignition timing, the two rotors are supose to be in sync with each other. Did this motor run smoothly before it blew??

 

I only noticed b/c I have done it before way back. My engine ran strong, with no troubles. I only noticed it is when I had an dowel pin o-ring leak and pulled the motor. When the engine was on the cherry picker thats when i was WTF? Even though the engine ran fine, I did match the housings when I rebuilt the block; and honestly I couldn't tell a difference once the engine was back in.

I really dont think that this is what blew his motor. Although the spark plug location is different, timing is still being taking from the position of the rotor/CAS. Maybe Mazda moved it for better combustion, i dunno.

You can swap rotor housings from different series, just have to swap them as a set.

BTW, his front is an S5, rear is S4.

 

No, I know for a fact you can get up to 300rwhp out of the stock injectors, and since this is going to be a daily driver for a bit before I strip it down and get it ready to race, I don't feel the need to spend the extra money yet when I already have many things in the shop I can just throw on for the time being.


The motor ran like a champ. I mean if it didn't run fine before I would have checked out a lot of things before I just continued to drive it. Like I said, the motor broke down in kind of an all of the sudden moment.

Thanks. I was trying to figure if that could have had anything to do with it, and was trying to figure out why it still ran fine with the different spark locations. But that explained it without me thinking too hard. lol

 

kouki and zenki turbo have the SAME spark location , its only the knock sensor

its the zenki NON TURBO that has the leading spark 5 mm higher towards the centerline S4 T and S5 T have the SAME spark locations the s4 NA does not.

This is an S5T motor with an S5 front housing and S4 NA rear.

With his setup this would hardly be noticeable in fact not noticeable at all. The timing of the motor is still the same as mentioned above it is not controlled by the plug locations. However the physical timing combustion locations are slightly different. As each rotor fires individually of each other every 180deg the differences would be no greater then say one rotor carrying more or less compression then another. As we know per the FSM we are aloud up to 25psi of differences. In my experience anything reaching 20 is fixing to pop. If one had gotten serious in power with stand alone's the tuner may begin to recognize possibly one cylinder making more power then another or running slightly different AFR range. This however could even be tuned out but the likely hood of this even being a factor is slim to none. This is not to say it's acceptable to practice your building in this manner it is only to say the effects he will see in this motor are the cause of him blowing it is slim to none.

$50 forum bucks says he had a cracked gear when assembled and it finally gave way or he over rev'ed it.
Umm yeah, no way is that ever going to happen.

 

S4T are not the same as S5T. Heres my pics from another thread about the subject. Even though my pic shows S5 N/A housing, shows that the S4T has same location as S4 N/A https://www.rx7club.com/showthread.p...81#post8922981


Banzai Racing gave a good explaination of some circumstances.

Only if you were running 6 stock injectors

 

i read on pineapple racing that its important not to mix the housings because it changes the ignition spark timing..but i dont know from personal experience so i really cant argue that point..to the OP the fact that you have a half bridge port and your running stock injectors is kind of a joke..

 

We will be using 2 S5NA housings and 1 S4T housing here. These pics were taken 5 minutes ago in my shop.

Here we can see my bench is perfectly level


by the marking we can see the far housing is an S4


Exhaust ports verifying


Spark plug holes


Now as we can see the plugs are perfectly level and aligned