WondrousBread

I took my engine apart (no compression on rear rotor) and I'm curious if people can help make sense of what happened inside. I've never taken apart an engine before, so it's all new to me, but it certainly doesn't look like anything I expected.

I have pictures below, but first some background:

The engine failed in my driveway. I was in neutral and I blipped the throttle, then it let go just as I crossed 2000 rpm. As mentioned, compression on the rear rotor was zero. It would still start and run only on the front rotor, which had about 90psi of compression. When I bought the car (a few years ago), I was told that this was the second engine. The owner was not clear as to whether it had been replaced outright or rebuilt with existing parts. In hindsight I should have asked more questions, but it was my first car and it was cheap. The compression test when I got home after buying it indicated about 100 psi on each rotor. After the engine blew, I did find some metal dust in the oil pan. No previous oil changes showed anything like that. I always changed oil on time and used premix (OMP still in place, the premix was a precaution).

Now, some pictures:



The front iron has a compromised coolant seal track. It was cracking when I took it apart, and light pressure broke it off completely. This was a bit weird, since my car didn't consume any coolant. It's also pretty clear from the brown deposits that this engine had tap water in the cooling system for a long time. Step wear looks like the pictures I've seen, and like the spare irons I've been keeping in the shed. Again, this is all new to me.



This is where it starts looking unusual to me. At either side of the housing, it isn't weird to see some chrome flaking. Instead, I have gouges. The picture doesn't convey the depth very well, but you can feel it with your finger and know that material has been gouged out. It's still shiny. I figured that maybe I would be looking at a situation where the rotor had wobbled and dug out these gouges, but;









This is the front rotor after a quick cleaning (you can still see crud in the grooves). The bearing looks alright, and I don't see any evidence of the tips contacting the housing. I know aluminum housings are softer than cast-iron rotors, but I feel like there would be some evidence if the rotor was gouging the housing that badly.

The center iron looks normal (again, usual step wear):



Rear housing:



Some of the brown deposits are oily and wipe away, but this housing has the same gouges as the front. This set me thinking that maybe the e-shaft was bent, but the rear rotor (not pictured, it's still not clean yet) is in comparable shape to the front one. No weird wear or damage. Bearing looks okay.

Rear iron:



The coolant seal is broken in the bottom right hand corner, but otherwise nothing seems too unusual.



And as for the e-shaft, the lobes don't seem to have any unusual damage.

The front and rear stationary gears have some slight wear on the bearings (not pictured).

Finally:





I'm not sure how well this translates in the photo, but there is a raised nub on either end of the apex seal. Presumably, this is the place where the housings were gouged. All of the apex seals look like this. They are the 3 piece style.

So that's that, and I'm not sure what to make of it. I had two places where the coolant seal was compromised, but no coolant consumption. I had two places where it looked like the rotors were gouging the housing, but no evidence of this on the rotors or bearings. The only thing that would make sense to me is that the engine was rebuilt at some point using new seals on housings that were already damaged, and it took awhile for the damage to cause complete loss of compression. That seems unlikely to me since I would expect that scenario to cause gradual loss of compression, not zero. All my seals were present and intact, so I'm not exactly sure what to think.

At the end of the day, all that matters is what is in spec and reusable and what is not. But I'm curious if anyone had any thoughts as to what could have caused this.