Quick background: With 100k miles on the car, previous owner had motor rebuilt back in 1985. Engine now has about 30K miles and started blowing oil into the intake plenum bigtime and running poorly. I checked the compression and got 73 PSI in cylinder three with 145-150 in the others. Did a valve adjustment (most were slightly tight but not bad) and compression came up to 80 PSI in number three with the others staying about the same.

Dropped the engine today, pulled the head on cylinders 3 and 4 and here's what I found:

Combustion chamber #3 cylinder

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Here's chamber for #4 cylinder for comparison

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Not sure if it's related but exhaust valve spring for cylinder #3 was discolored with what looks like burned oil while the rest looked nice and shiny

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Cylinder 3 piston and bore

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And cylinder 4 piston for comparision

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I'm thinking leaking rings on cylinder 3 is the cause of the oil in the plenum and inside the cylinders as the valves in that cylinder seem to look OK unless I'm mission something. Very interesting in hearing any thoughts as this my first time going inside the engine like this.

Thanks,

John

Bad rings shouldn't blow a lot of oil into the intake plenum. If your valves are too tight maybe. If your blow by is so bad... maybe. That's really bad blow by.

Well John, I would say your correct. Looks like oil everywhere. I looked really close at your #3 ex seat and I can't tell if it is coming lose or it's just some sort of shadow. Look at it with a magnifying glass.

I know nothing about nothing but does it appear piston may be a bit undersized for the cylinder?

seems like your heads were sealing very well to your cylinders.

More than one thing wrong here. Valve guide is likely poo, too. Who did the rebuild? Shop or amateur? Rings need to be checked. You have a lot of crud on all of the cylinders, though. Burning oil sent through the plenum?

The rebuild was done by a supposedly reputable independent Porsche specialty shop in Santa Barbara, CA back in 1985 but I can already tell they didn't use all the new OEM parts supplied by the owner to them for the build. The reason I say that is I've already found mismatched rocker arms in the heads but I have receipts from PO which show a full set of new rockers delivered to the shop. Also other EFI parts on the engine seem to have been simply brushed with silver paint rather than replaced with the new part supplied by the PO. Not very encouraging to say the least.

My current theory is rings in number 3 are shot and they are blowing oil back into the intake plenum which is then redistributing they oil into the other cylinders. Is such a thing possible? Is there a way to determine if the rings or the valve guides are out to lunch?

Well the good news is the engine drop went quickly and easily - no yelling, no screaming, no profanity, and no trips to the emergency room... Damn, what a boring morning

All four intakes were oily and nasty, but I assume that's due to the plenum oil field (I was ready to put up an oil derrick through his throttle body).

I'm no expert on heads and valves, but there was nothing glaring there to explain a 75 pound compression reading. It was interesting that on the bottom of the head (top of the photo) on cylinder four there was a large trace of oil seeping out but no signs of blow by, and compression was in the 150 range on that cylinder before and after John adjusted the valves. There is just a small trace of oil seepage on #3.

There was no scoring or other signs of damage on the #3 cylinder wall. Time to pull the jug and take a look at the piston/rings. Also before we pulled the engine, there were no real signs of oil oil burning out from an exhaust perspective. But she was just a bit off in the performance/smooth running department.

Oh, one other note, before the valve adjustment, we removed and reseated my compression gauge a couple of times to ensure it was seating. Also did that after adjusting valves so I'm confident it wasn't a gauge issue.

Good comment by Jim Kelly - have to take a closer look at that.

I think what John is saying is that the case is over pressurizing due to ring blow by, then oil vapor is forced out through the PCV and collects in the plenum.

Pull the hose from the PVC valve, and post a pic.
It could be a bad or broken ring.

Why would anybody replace the whole set of rocker arms? It's not like they go bad ................

The Cap'n

I pulled the PCV when I first noticed the oil in the plenum and although oil saturated it was intact. The spring loaded flap at the bottom was also intact and seemed to be held flat against the bottom by the internal spring. I didn't want to break it apart until I was able to source a new replacement. Unfortunately I have yet to find a source so I guess the PCV goes on the ever growing NLA parts list for our cars.

Pull the cylinder off and have a towel underneath to catch pieces of the ring.

See if you have a broken ring or broken ring land on that piston.

It's simple enough to use a proper ring compressor to put the cylinder back onto that piston, or pull the piston and do that on the bench, then insert the wrist pin into the piston while it hags out of the bottom of the cylinder...

Keep digging.

Quick check. Turn the head upside down.Secure it. Pour a bit of varsol into the head. See if any of it leaks past the closed valves.
That and look for broken rings.