Fluids came out today. Engine is nearly ready to come out-- Power steering pump & AC compressor left to take off.
While draining the oil, there was absolutely zero metal shavings on the drain plug, zero shavings in the pan, and zero shavings in the oil filter...
Frankly confused by this result as I definitely have no compression in both rotors. Is there another possible failure point that could cause 0 compression in both rotors that wouldn't produce metal shavings in the pan?

Beginning to think it could potentially have been loss of oil pressure, ignition/injector failure, ECU failure, or a harness breakage?
What's very weird is that BOTH rotors don't seem to be making compression, not just one which should all but rule out the injector/ignition system.
The car wasn't leaking any fluids after the engine gave up and both the oil and coolant looked perfectly normal.
Here's a photo of the oil filter-- any input is appreciated. Seems like I'm staring down the entrance to a really deep rabbit hole.
https://scontent-lga3-1.xx.fbcdn.net...8b&oe=60986A6D

You'd be surprised Dale, I've torn down a few engines over the years that showed zero compression on all 6 faces and the irons and e-shaft were all reusable. The rotor housings and rotors (and turbine wheel(s)).... not so much :rofl:

You will need to open the engine for answers to your questions. Typically a motor with broken seals won't have any oil problems - bearings are fine, no shavings in the oil, etc. This isn't a piston engine, broken seals stay in the combustion chamber.

On removing the engine, leave the power steering pump on the bracket. There are 2 hoses connected to the pump, use an extractor pump of some kind to get as much fluid out of the reservoir then unbolt the 1 banjo bolt and remove the 1 hose with hose clamp. It's WAY easier than trying to remove the pump and the pump pulley. That literally takes 30 seconds.

Dale

Thanks for the tip! I was hoping to get away with not taking the pump off so this helps a lot.

RIP Engine 1992-2021
https://cimg3.ibsrv.net/gimg/www.rx7...348ff50e93.jpg
https://cimg4.ibsrv.net/gimg/www.rx7...e2ee8d3e24.jpg
https://cimg6.ibsrv.net/gimg/www.rx7...84d72dd2c9.jpg
https://cimg7.ibsrv.net/gimg/www.rx7...25be6084ee.jpg
https://cimg8.ibsrv.net/gimg/www.rx7...538bb105da.jpg

I don't think that goes there :)

Have you opened the engine yet?

Dale

That looks like some foreign object went through the engine rather than the seal itself breaking

Wow that's odd. I am interested in seeing the inside.

Engine's gonna be opened up this weekend will post pics.

Tested injectors at the advice of a local rotorhead that has seen several injectors fail after being cleaned due to the water based solvent they use for cleaning gumming up the injectors. None of my injectors were stuck.
Tested Injector pins in the harness, all of my injector connectors have full continuity.

Beginning to think a possible culprit could've been the fuel pump. A catastrophic fuel pump failure could cause detonation in both rotors right?
Injectors, plugs, coils, harness all seem unlikely to cause this kind of failure in both rotors simultaneously.

Will test fuel pump next.
A stock ECU will be going in with the new engine.
If there are any other points of failure I should test please let me know.
Engine is going to be opened up tomorrow.

Sometimes there's no one thing that causes engine failure. You have a JDM car and you don't know the engine's history. The previous owner could have been doing burnouts in a parking lot and caused engine damage, you just don't know. Also possible it sat at a port for 6 months corroding in the salt air, someone rebuilt the engine in the past and did a poor job, a bad batch of gas, etc. etc. etc. The good thing is with a new engine going forward you will know what you have.

Dale

Opened the engine today. I think I have a decent picture of what might've happened now.

Fuel in the fuel lines was extremely yellowed, pumped out about a quart of super yellowed (deep urine color) gasoline before it got to good/clear gasoline.
This is likely what caused detonation, but not sure why only the fuel in the lines was yellowed. After a few seconds running the pump the fuel became perfectly clear.
Not sure if all that yellowing could have just happened recently due to the hoses being exposed to air for about a week.
If so, then I still have yet to know the true culprit of the detonation.

The front rotor experienced catastrophic apex failure (likely due to detonation) and blew the upper piece of the 3 piece seal to smithereens. A piece of the groove lip rotated 90 degrees and welded itself in..
The rest of the upper piece of apex seal was completely gone.



The reason I think it's detonation is because there's a trail of steel fragments & filaments embedded into the front housing starting from the combustion/spark plug area and ending around the exhaust port. (See below)
Additionally, 4 of the 6 side corner seals on the front rotor are also stuck flush with the rotor like Howard said they would be in a detonation event.
Due to being preoccupied with assembling the new engine I haven't yet checked if the corner seal springs yet to see if they are flattened like Howard mentioned is common.

Almost NONE of the damage suffered by the engine was anywhere near the intake ports and the major damage to the housings was not anywhere near the intake or compression areas of the rotor cycle.
Rationally this seems to rule out damage via foreign object entering from the intake ports, please correct me if this assessment is wrong.
There were also no witness marks in the carbon buildup from anything banging around on its way into the intake port, which was not the case for the carbon on the exhaust ports near where most of the damage was suffered.





Now on to the real meat and potatoes... the rear rotor... Avert your eyes....
Every single apex of the rotor had this same 2-3mm gouge in the exact same spot. The rotor housing was absolutely trashed. And all of the housing damage was centered around... the exhaust port...
Which I think means a big fragment of apex seal launched out of the front rotor housing at high velocity, bounced off of the far wall of the exhaust manifold back into the REAR rotor's exhaust port and proceeded to, for lack of better words, fuck my shit up.


The only light at the end of the tunnel is that the irons look more or less reusable to my untrained eye. There is minor scratching but the deepest grooves in any of the irons can hardly be felt by my fingernail. If anyone would like to rain on my party and let me know they're actually unusable then I'll go ahead and get the sad music playing.
https://cimg5.ibsrv.net/gimg/www.rx7...256db6dcf8.jpg

The E-shaft is also reusable along with everything forward of the front iron.

my coolant jackets were in surprisingly good shape for being 29 years old. Zero cracking and still very pliable and stretchable.
All other signs while opening up the engine seemed to point to this engine being very babied and never suffering major abuse.
Kind of mirrors my thoughts about the car when I saw the state of the AC condenser fins which hardly had a single dent in them from rocks/ etc.

The carbon buildup on the rotors looked pretty substantial to me, which probably was a byproduct of the car not being driven hard much. (1 owner car before being sent to auction, female in Japan)

It's such a shame that the motor had to go this way.. Just wish it rained that week in April so I wouldn't have blown up the motor... Cause for detonation is still unknown between bad gas, tune, or aftermarket ecu failure.

Turbos
 

I think my turbos might be ok. Turbine wheels don't appear damaged and they weren't smoking at all after the engine failure occured
https://cimg5.ibsrv.net/gimg/www.rx7...a63b2e1b3d.jpg
https://cimg6.ibsrv.net/gimg/www.rx7...fe1c92bdd0.jpg

Shouldn't have gotten my hopes up hahahahaha....
https://cimg9.ibsrv.net/gimg/www.rx7...95485e0113.jpg

Upon looking into the yellowed gas issue further I've come to the conclusion that what happened is my fuel suffered phase separation which caused detonation.
Like I mentioned in a previous post, about a quart of gas that game out of the lines when testing my fuel pump was urine yellow which made me look into the phenomenon. Learn something new every day.

Guess I've learned an expensive lesson about bad gas. For whatever reason the fuel stabilizer failed to do its job and the octane booster probably didn't make any difference in the garbage that settled at the bottom near the pickup.

My sorry ass isn't going to be revving up a car on old gas anymore under any circumstance..
Throwing out a tank of gas after every winter is still gonna be cheaper than having to replace another engine due to bad gas.

Glad you took the turbos apart, that is very common for apex seal failure. Looking at the exit side of the turbine it looks fine, but the sides is where the damage happens. FYI those turbos WILL work but they will spool crappy and start smoking fairly soon.

You are not alone here, I've taken MANY engines apart that look like yours after detonation breaks a seal. The old 3-piece apex seals are also MUCH more prone to breakage and the top portion can rock in the groove. I think that may be how the front rotor went.

Yeah, irons look re-usable, if you want to do a budget rebuild you can get used rotors and rotor housings and there you go. The rotor housing and rotors are JUNK, unfortunately, there's no saving those.

Build it back better, fix anything on the engine that needs doing while it's out, and be happy with a motor you KNOW the history of and KNOW it's all done right.

Also if you had 3-piece apex seals that is 90% sure it's the original engine, Mazda hasn't sold those in ages.

Again, don't sweat it going. It was going to happen at some point. Get it fixed nicely and move forward with a setup you can be happy with.

Dale

As some of the Google references said, keeping the water out is the 1st and best method of preventing water/alcohol phase separation. I've stored my FD over the winter for most of its 29 years with the tank close to full (E10 93 since it became the norm for street gas) in a heated garage where humidity is usually low and temperature changes are small. This keeps any significant amount of damp air from being pulled into the tank, water condensing and causing this phenomenon. I also do the same with my racecar (also E10 93), which does not have the semi-sealed tank which street vehicles have. No issues there either. If you store the car properly, the gas will not have this issue.

Storing a car outside or in a non-heated garage is a recipe for phase separation, especially if you don't keep the tank full or at least use it regularly. YMMV

Thanks for the tip Dave. As far as following those suggestions, it's gonna be hard for me. I have no garage and most of the fuel near me is e15 93. Hoping to buy a house with a garage in the coming years but a garage in NYC costs about what a house costs in the rest of the country.

Thanks Dale.
The rotors and housings will become decorations. As far as reusing the irons and other components... I think it'll be a long term project

Well, at least you can try to keep the tank as full as possible. That minimizes the air volume that can expand or contract with temperature changes. It's that expansion and contraction that sucks in moisture and causes the problem. Or maybe you can find a station that has ethanol-free unleaded gas and fill with that for storage. They're rare, but they do exist.

What's the plan for the engine at this point?

Dale

New one is on its way back in. Got the motor delivered last thursday and I've been working diligently on it but I kept getting rained on all weekend.
Getting real sick of working on the motor wet and cold. Bought one of those 10x10 tents but the thing broke from the wind..

Just swapped the cracked hot side housing off the ebay replacement twins with the one from my damaged turbo. I think this frankenstein set of twins should be good to go for a few years. It has almost no shaft play.

Old bits are gonna get a coat of oil and get stashed away.

Good plan. Just be certain to take care of any little thing that you notice while putting stuff back together - new OMP lines, any new gaskets, etc. Get it all nice and happy and you won't have to worry about things for a long time.

Dale