Tmm20

Long story made painfully short;

86 928s 32v

Cats hollowed out, air pump removed two years ago, no issue listed were present prior to the engine seize and intake rebuild and the car was a daily driver until the engine seize.

Engine seized when cranking last year-ish. Sat all winter and freeze/thaw cycles freed up the block to where I could finally break it loose with a 4ft breaker bar and turn engine over.

Complete intake refresh performed, fuel rails rebuilt, etc. Engine starts and idles flawlessly solid idle and fires first crank every time.

Issue is now that the intake is filled with an excessive amount of oil. I know already that oil in the intake is normal, but this is beyond acceptable. Enough oil pools in the throttle body that you can almost dip your fingers to the first knuckle in the puddle. Lot of oil collects in the intake side runners/plenums as well.

Engine smokes excessively at idle, worse when letting off the gas after coasting.

This is 100% oil smoke, absolutely not coolant.

Ive heard talk about piston rings being trashed by the seize, and/or a bore being trashed by scouring from the seize. Also heard it could be valve guide seals. I do not believe this is the issue due to the fact that the oil would need to come upwards against gravity and air pressure to somehow reach the throttle body and intakes. This goes against everything logical and reasonable to assume it is either of these issues. Also, the engine runs much too smoothly at idle for me to believe a cylinder or more than one cylinder is trashed.


I believe the oil is coming from the filler neck vacuum lines, or the passenger side valve cover vacuum lines. I cannot narrow down which because there is oil absolutely everywhere in there.


Anyone who has anything to add please assist/advise. The next step is either to swap to a Chevy 350 or LS motor, or sell the car. I would be happy to just stop the horrible clouds of oil smoke at idle, I do not care whatsoever if the engine continues to burn the oil.

Could a missing seal on the oil dipstick tube cause these issues by allowing air to be drawn in through the oil pan and pull oil up through the engine? I will be grabbing a fat oring and resealing the dipstick tube prior to anything more indepth.

davek9

What does a compression check tell you, what are the readings?
Then do a Leak down test and see which way the pressure is venting, crank or valves.

Tmm20

Please explain your reasoning why either test would assist with oil in the intake, which is above the valves and cylinder and at positive pressure compared to each? It would be very unlikely in my opinion that rings or valves would somehow put oil into the throttle body and intake.

I am going to rent the compression test tool and perform the compression test but I will not be doing a leakdown test as that is too involved and in my opinion will not in any way explain oil in the intake, which again, is higher and at positive pressure compared to everything below that a leakdown/compression test would be checking.

Edit; I also know for a fact the valves seal great, because oil that eventually drips down or is poured down to the valves does not get through them and instead sits on top and never drains through.

Cosmo Kramer

Excessive pressure in the crankcase due to blowby can cause excessive oil in the intake. If your engine seized I'm sure your rings aren't sealing like they used to. If the car runs good otherwise you could try adding a provent to separate the oil from the crankcase vapors.

Also for the price of an LS swap I would find another decent 85-86 lump if an engine is needed. With Ken's chips they put close to 300 hp to the ground.

Tmm20

Respectfully, I will not be replacing this engine with another 928 block if I bother to swap engines. These engines are too expensive to maintain, too complicated for the limited power they can top out at without massive cost, and performance upgrades as mentioned that actually are actually available are ridiculous price for limited gains. A 350 or Ls swap allows me to buy replacement parts at any part store, in stock without waiting on order, and at massively reduced price and increased reliability.

FredR

There are only two things I can think of that can cause the crank to stop rotating - either a seized main [or possibly a big end] bearing or seized piston rings.

Is the car an automatic or a manual? There is a known issue with some autos wherein the thrust bearing can seize. However when this happens ring damage is not likely, disastrous as this issue is.

If the rings have seized and somehow been freed up do you not think the chances of mechanical damage or more or a racing certainty? As Dave suggests, first step do a proper compression test across all cylinders with the motor warm and the throttle fully opened but make sure the engine cannot run and is cranking on the starter motor- then feed back the findings.

Rgds

Fred R

Tmm20

Manual, no concerns of main damage. It was definitely a seized piston I am positive of that, I heard it make noise when it finally let go. I'm not in any way disputing that rings could be shot but I still need someone to explain the logic how bad rings could get oil in the intake. It just doesn't make logical sense. Blow-by would raise crankcase pressure but that's a long way for it to go to make it back up to the intake all the way through the engine and then burn from there. Every other experience I've had with bad rings burns the oil right in the suspect cylinder and never fills the intake with oil. I simply cannot follow the logic that is supposed to explain that.

davek9

Because without TESTING and measuring you are just guessing and stabbing at an issue looking for an easy way out, and there is not.

As for the leak down, yes it is a bit more involved but it will prove that the compression is "blowing by" the rings creating an excessive amount of crank case pressure and blowing it into the PCV system and thus into the Intake.

Tmm20

I said I'd be doing the compression test, but the leakdown is likely not something I am going to do. I know for a fact the valves are fine, as much as it sounds like I'm full of it by saying that.


Edit; this makes me miss the 944, rod knock and all its problems combined.

I know it is illegal, but I can get inspection stickers "slapped on"; what would I need to do to simply vent pcv vapors and pressure to the atmosphere? Cap the second oil fill neck lower port, and route the valve cover vacuum line to an exit under the car w/ a checkvalve to prevent ingestion of anything?

FredR

The action of compression alone raises the cylinder pressure close to 200 psig- when the mix ignites the pressure goes somewhat higher to generate the motive force. If the rings do not seal correctly whatever combustion pressure is generated will go flying past the piston skirt into the crankcase. All these gases will take the path of least resistance which is through the breather system that recycles via the inlet manifold and a shed load of oil will be taken with it.

A compression test followed by a leak down test will tell you how extensive the damage is likely to be and where it is cylinder wise but by the sound of it, if know the piston is seized then for the time being at least the motor is goosed.

If there is no issue with compression or leak down then you would start looking elsewhere for a problem but at the moment based on what you have told us that [no piston issues] seems highly unlikely.

Tmm20

I'll do a compression test tonight if they have the tool in stock for rental at pep boys. Would you not agree that blow-by strong enough to cause this much oil in the intake would cause issues with idle and running, which I do not see? The car runs absolutely fine - exactly as it did prior to the issues - the only issue apparent is the oil smoke from oil in the intake. Is there anything I could have damaged when I had the valve covers off that I don't know about? (I am assuming the answer is no based on my knowledge)


Edit: also if the rings are simply stuck and not physically broken, would a long drive (100 miles) at highway speeds possibly free them up and resolve the issue, I've been suggested to try this as well. The smoke is not visible at all when driving only at idle.

FredR

With the 8 pot motor 1 buggered cylinder leaves 7 good ones. With 1 cylinder completely down the motor will still idle.

You came to us for advice, you have already had a several good responses and if you carry out the steps advised it should help prevent you from doing anything that is not strictly necessary.

If you have low or no compression on one or more cylinders then no point is testing further. If compression pressure is more or less OK a leak down test will help define the problem better. If the leak down test is OK as well chances are you will not have to remove the motor to solve the problem [whatever it may be].

FredR

if the rings are gummed up the question is why? Overheating can and does cause engine oil to carbonise and thus stop the rings from working. To undo such status I suspect some kind of chemical solvent would be required to soften/loosen the carbon- whether or not the problem can be reversed after such has happened remains to be seen- personally I doubt it but..?

You also said you thought there was piston damage- why? Any idea what happened or went wrong to cause a problem?

Tmm20

I'll do the compression test tonight provided they have the tool. If a cylinder is dead the engine is done for me - I am not doing rings and I am not swapping in another 928 block for reasons quoted in my post above. I realise everyone quotes the standard compression/leakdown but let's be honest with each other - a leakdown test is not going to further assist this diagnosis. Compression test will tell me if the rings are shot. The valves are fine, and valve sealing issues would absolutely without question and beyond debate not cause oil in the intake. It could only be rings doing this, i think we have narrowed that much down, and a leakdown would only tell me the same thing as compression when it comes to rings, can we agree on that much?

I guess I seem flippant or dismissive based on the tone of your response - which is not my intention at all - but I have been working on 944s and 928s going on six years or so now. I know the value of the applicable tests and know the car well. I guess the pcv system really is so poor on the 928 that bad rings would do this, its just not the norm. I've never taken a single car of mine to a shop and my wrenching experience is expansive and I've never seen bad rings blow oil into the intake via pcv.

Again, please don't take me the wrong way. Its hard to get tone and inflection across in text.

Tmm20

The car wouldn't fire in the dead of winter last year and the engine seized because I got pissed off and cranked it for far too long - no excuse, that is 100% on me. It was my daily driver and caused me to almost lose my job, actually, which is why I got pissed off and cranked it until it locked up.

It made a clear and obvious creaking noise from the cylinder area on the rear drivers side of the engine when it broke free. It is definitely firing on all cylinders based on the plugs which were replaced prior to restarting it after the engine was broken free.

There's probably ring damage, but I was hoping for the best because I am not doing the rings, and I am not swapping in another 928 block due to reasons already mentioned in my posts above.