Liquid oil in the exhaust.... and other oddities
 

Hey y'all;
I need some help, and it seems I've diluted my AOS topic enough that this specific issue hasn't attracted any attention. Either that or nobody has an opinion.... which is hard to imagine, haha.

In my "AOS, what breaks first" thread, I've described the situation surrounding this specific question, but to nutshell: I've got oil in the exhaust. I still seem to have good compression in all cylinders, and no obvious signs of intermix. This could be simple catastrophic AOS failure, but there's still one issue nagging at me, keeping me from diving in:

Note the photos below. Large cam plug on the front of intake cam on the left bank is MISSING. Both small cam plugs on the back of the same bank are canted/ crooked. I can't account for this. It's almost as if they've been pressurized and blown out. I've been trying to imagine ways that crankcase pressure could reach those levels, and none of my imaginings are pleasant. None of these areas show obvious signs of oil dripping from those holes, but there is signs of weeping, and the foam sound insulator opposite the missing plug is saturated.

Can y'all please help me with your experience here?

What could have caused this?

Thanks.

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I can’t speak to the left side but once had a cam plug fall out of the right side of the motor and it pumped quarts of oil out in a matter of seconds. Odd that you can run without them. That being said if they popes out it’s more than likely a pressure problem which points to the AOS. Id replace the AOS and the plugs (MAKE SURE they are well hammered in, not like your photo) and then send it.

Are you sure the engine didn't spin the wrong way as a result of the car spinning and then traveling backwards?

Something caused a lot of pressure to build up.

No, I'm not certain. The car died when I spun. That may be from what you describe. It happened pretty fast, as it was precipitated by the oil left by our friend in the Ford. :: sigh::
Don't get me wrong.... I blame only myself for the spin, but the conditions leading to it have to be acknowledged too, haha.

So, if the motor spun backwards, what's the biggest fear here?




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Bent valves....

Right, but that's assuming cam timing changed, which could've happened forward or backward, yeah? (Or is there another way to bend those valves that I'm not considering? )
But I'm still pushing healthy compression numbers in all cylinders.

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As far as what fails in the AOS, it seems to be the rubber diaphragm that splits.

You may have escaped damage - I'm just postulating what blew out the plugs...

In the end this was an atypical AOS failure. We have all seen smoke, exhaust oil fire not so much.

Rotating the engine in reverse, even by hand, is sufficient to whack the valves; we have had people bring us cars that they had done exactly that while attempting an IMS retrofit, and even though the cams were still in time, they had kinked a couple of valves and every piston had bark marks from contact.

!!!??!!!

I believe you, JFP, because I have no experience otherwise. But I'm struggling to wrap my head around the HOW.

The location of the cam (and therefore the entire valvetrain) is fixed, in relationship to the crank (and therefore the pistons). I'm trying to imagine how direction of rotation can affect this? Teach me.


Hahahaha.... I'm rarely "typical" in anything, Max. Surely you've understood that about me by now, haha. :cheers:

I think it's time to break the borescope out.

slack in chains.

yup...on it tonight.
BUT: a bent valve isn't consistent with good compression numbers. Jus' sayin'.

seriously?
Is this something you've seen? or are you postulating?
Shouldn't the chain tensioners be working regardless of direction of rotation?

The chain tensioners function off oil pressure, when the engine is turning backwards, the oil pump is sucking the oil out of them..………..

it can happen in older engines due to stretched chains. recall that on our cars we get chain slap on start up due to low oil pressure and the tensioners, like lifters, require oil to inflate, so without oil pressure there is some slack in chains.

While the pic attached is of a 5 chain engine and yours is a 3 chain the mechanicals similarities should be evident.

On these engines the chains have a "driven"(under tension) and a slack side that the tensioners control. The vario cams can move ~23 degrees in relation to the crank and you see how short they are. How many degrees backward does the crank move before all the slack is pulled out of the crank to IMS chain and the camshaft drive chains on the slack side? JFP might know but it would be considerable. Obviously enough to interfere with piston travel.


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aaaahhhhhhh..... Bach. ($5 to anyone who recognizes that reference, haha)

Okay. thanks to Radium King, JFP and 911Monty, My eyes have been opened. YEah, I can see it now... makes total sense. that ALSO leads me to understand what MaxD was getting at, about the engine turning backwards....

y'all are a wealth of knowledge here.

now, excuse me while I back-up a little bit, as I take a long look at the way Porsche engineers designed that entire system, and shake my head in wonder. (as in: I wonder why in hell they still had jobs after that mess?) :confused:

Of course, I've seen worse, because I've owned Jaguars, RangeRovers and Maseratis. :rolleyes:

In your previous thread, Post #12, I asked if you got the clutch released before going backwards in your spin when I asked about the scavenge pumps. Have you checked their condition? The sources for pressure in these engines come from compression/combustion, thermal/ water, and mechanical/ oil pump. Since you don't have water in the oil there is really only 2 sources you need to evaluate for pressure in the valve covers. The AOS is a source of vacuum not pressure. It is basically a regulator between the intake vacuum and the crankcase.

Well that's just a mash-up of where it could have come from. ;)