Oil Ring in the Sump

[patkeefe]

Three weeks ago, I had the SC at Watkins Glen. First run group, it was a bit lean, so I came in and adjusted the WUR, which got it acceptably rich according to my AFR gauge. It warmed up some more a bit later, so I had to repeat the process, this time I had to lean it a bit. I did also notice I was getting what seemed to be a bit more crankcase pressure at the oil tank. I thought about it, and figured maybe I had it so rich that I may have washed some oil off the cylinder walls or something stupid like that. Anyway, I felt no cause for alarm at this point, figuring one more run and see what's up after that.

Just before lunch, the car was making as much power as I have ever felt in it. I was screaming up the esses on top of 4th gear when the car filled up with oil smoke. I shut it off and blindly coasted to a stop, and of course, put the fire out on the heat exchangers, as I had dumped a bunch of oil. Made a mental note regarding new Nomex suit. They towed it in, and I put it in the trailer, and ignored it for 10 days. I have not run it since, although I did turn the engine over via the starter.

I thought maybe I had a leak in the turbo feed line, but couldn't find evidence of it. So, this week I drained the tank...a half inch bit of oil ring came out. Real good for the oil pump, I thought, as I started doing damage assessment in my head. Another 3/4" bit came out of the sump. Crap!

I'll get the engine out this weekend, and see what's left of any use.

I have some speculative ideas as to what broke, just don't know why at this point. I didn't see any compression rings, or piston bits, just oil ring. I was only running 7 PSI boost at the time. Documented failure analysis to follow, for posterity. I am having trouble correlating broken oil ring with massive loss of oil, however, unless the crankcase pressure blew out the oil seal at the crank (doubtful).

It may be time to just get a real 930 engine for the car, or put cams, pistons and carbs on the 3.0, if there is anything left worth a crap in there. I have grown acustomed to the boost, so I don't think I want to revert back to n/a. We shall see.

[mb911]

you just really need the correct pistons and cylinders then you are fine. 1 thing you could do is run 930 P&C's and send the rods out for modifing for the larger wrist pin or even offset. the whole set up could be done for less then a grand then you can crank up the boost and have a better bottom end then a 930(stock)

[A930Rocket]

Could you have burned a piston and/or cylinder and ring parts fell into the case? While AF ratios were good, did it over boost at all?

[patkeefe]

I suspect piston damage somewhere, and I may have overboosted it. Just losing an oil ring is a somewhat odd failure, and that in itself doesn't explain the severe loss of oil. I believe I still had oil pressure when I shut it off, although I am not 100% sure of that. It was kind of hard to see the gauges at the time, as my main thought was to keep it off the inside wall. I had absolutely zero visibility save for a small bit of the bottom left corner of the windshield.

It looked like the oil dumped from the top front of the engine, which is where my turbo feed line is.

[rsrmike]

You may only be seing the oil rings right now as they are the least robust and most likely to migrate

Certainly sounds like piston failure.

Did you hear any detonation?

What sort of ignition timing are you running w/ SC compression & boost?

Perhaps you have a lot of carbon on the pistons, that will certainly aggravate detonation in an an already hostile combustion chamber. That may have attributed to the sudden failure.

It's hard to get the pistons as hot anywhere else as you do on track and you may have had a "glow plug" effect going on.

That stinks man, I'm sorry

Good luck sorting it out, keep your chin up!

[patkeefe]

Well, detonation seems to be likely culprit. Won't know til I get it apart. I do use old SC compression of 8.5:1, and I have water injection. My actual theory that I have been mulling over is a clogged piston squirter, ensuing higher temp at one piston bottom, and isolated detonation in that cylinder.

[930gt-40r]

Pat, if you are interested I have the stock cylinders that came off of my 3.3 motor- they need to be replated though. I send you the lot of 6 for 50 bucks if you want them. Oh they are flame ringed as well.

[patkeefe]

Well, I got it apart a bit; left side heat exchanger. I saw some shiny debris in the exhaust seat/valve interface on the #2 cylinder. Also, the main oil seal has a crack circumferentially in the rubber...guess that's where all of the oil came out. Maybe I can get it torn down tomorrow.

[patkeefe]

Here is the extent of the damage thus far. Only piston #2 is broken. I have no idea why, unless the land just got weak. I don't really see any signs of detonation. I am open to opinions, of course.

[mb911]

looks like weak piston. They are cast unless you go 930 P&C's or JE's . I would guess just overstressed parts