kael

So, spent yet another winter chasing some issues on my '87 Lady, including the old oil gulp problem. Losing a lot at interstate speeds, as in a quart in 120 miles last trip, was 1 quart per 800 or so before. Around town driving, even for lots of miles, no where near as much. Also, #2 spark plug fouled, first black dry followed by black oily.

After all kinds of this and that (idle adjust, intake manifold gasket, vacuum vacuum), this spring She fired nice. First 120 miles or so, oil stayed spot on, no loss. This included at least 20 miles of interstate, maybe more as I forget how many test trips I did.

Last couple of town trips, noted a miss or two now and then. Took road trip last weekend, 64 miles mostly at highway or faster (no, not above 80). A pint of oil was gone. Misses at idle every few seconds, sounded like #2 was junk again. I've replaced and chased what's up with this cylinder for two years.

Checked plugs today, all but #2 are fine, old problem plug is looking oily but not too black yet. Dammit!

Checking mileage and logs, I've got about 200 miles since the garage this year. Ran fine for about the first 100. Seems all was okay until #2 fouled.

So, what are the odds it's the piston rings are shot versus say the distributor or something else? I've replaced tons already; heads removed and machined with new valves, with new valve seals. Tried three different spark plug wires to #2. Replaced EGR valve. I've checked compression and leak down, not too off from #1.

What else would foul a new plug in 100 miles? Wouldn't a leaky piston be faster than that?


Obviously a rebuild is something I want to avoid for another year or two. Stupid wallet.

confab

I got mine and the engine was a "rebuilt" 355, but it sat for a long time.

It never ran right. I did a compression check on it and a couple of cylinders had 75lbs of compression. It's newly "rebuilt" right? So what could be the problem?

I took it apart and it was, indeed, a rebuilt 355.. But the piston rings had stuck. Stuck hard. That was the only problem in those cylinders. Something caused them to carbon up and stick.

Could you have an intermittent problem like that after storage?

Others would know more about this, I am sure.. But if they aren't completely stuck hard in their grooves, could soaking them with something and regular driving help loosen them?

383vett

How many miles on the motor? A leakdown test will tell you where the oil is coming from.

mtwoolford

You're preachin to the choir; I agree 100%

I'd take out all the plugs, set the offending piston at the bottom of its intake stroke and fill the entire cylinder with the penetrating oil of choice. Let sit for as long as possible. place a spark plug in that one cylinder and rotate the engine BY HAND until it compresses the penetrating fluid, and once the initial bit of fluid leaks down past the rings and ring gaps, compress it a little more; repeat.

Eventually the piston will be at TDC on the compression stroke. Remove the spark plug

Repeat the procedure on any other suspect cylinders.

Of course, change the engine oil and filter. Refill with a quality all synthetic oil

This type of problem used to be common on engines back in the "bad ol days" when motor oil was made outta dead dinosaurs instead of in a chemistry lab.

confab

That's a good plan. I'll remember it for future reference.

Although mine were stuck so firmly that it showed up immediately on a compression test, they weren't always firmly stuck. At some point they were beginning to stick and that could describe the "on and off" poor behavior in the OP.

kael

Hmm, I think I missed mentioned She drives. Starts fine, runs fine until the foul, then just burps some (tiny sound), but runs okay. Even at fould, sounds fine when driving, as far as I know. Cranks good.

Currently 61k on the motor, got Her with 52k.

Again, leak down was the same for #2 as #1. Compression as well.


I suppose fuel additives like Sea Foam are naughty for chasing carbon on rings?

383vett

If you have oil in cylinder #2 and the leakdown test is fine, the oil has to be coming from the intake gasket or valve seals because the rings are ok. You said the heads have just been done? If you are sure of the quality of the work, you might want to pull the intake off and hopefully you have a gasket that isn't sealing and pulling oil up from the valley.

confab

There was a guy with a garage up the road.. I walked in and the whole damn place was filled with smoke. I really thought a car was on fire in the back. I could barely see it for the giant cloud.

He came walking up and he didn't look worried. I asked him what he did and he said it was "Engine Bright" (I think?) to "remove the carbon"

I dunno if it works, but it would be a lot of fun for the kids on the 4th of July..

mtwoolford

There was quite a long thread a few years back about a gentleman who had spent $$$ on a high end engine build and the engine used about a quart of oil every 100 miles. He was not happy. The long and the short, after trying every conceivable remedy, he finally removed the intake manifold and found two pinhole casting flaws in the intake runners of the head that allowed oil to be sucked into the engine.

So an intake gasket failing could be a possible culprit.

kael

I've replaced the intake gasket twice.
One year ago.
Couple months back.

#2 had this problem through all three gaskets (hence why I went after in the first place).

I removed and put the heads on myself, including new valve seals. Had a machinist check and address the heads. He said they looked great, replaced three valves.

Guess I'm stuck with piston rings as the cause. Just don't understand how it would take 100 miles of runtime to start leaking. For the 100, I would check oil every morning if I drove the day before, stayed right on the mark for the 100.

kael

Ah ha. Something changed.

Dropped in a new plug and drove around town for 17 miles. Metro driving sure stacks up quicker than my old tiny town.

Anyway, pulled plug this morning, already getting some of black on the arm and electrode is dark brownish. And last bit, lost a few ounces of oil. So, it's not the same as last month, zero oil loss for a while. Something went bad.

ctmccloskey

This is probably a wild shot in the dark but I have seen cars loose their oil because their PCV Valve was stuck. Remove it and verify operation or just replace it.

Could one of the valves oil seals (Umbrella Seals) in the re-worked heads stop working? If they were not put on properly it could cause issues like what you are experiencing. This should be able to be checked after removing valve cover.

When you get pressure inside the motor it can either burn or expel the oil. Frequently an oil seal will give up and start blowing oil out. Then the engine locks up.

I hope that you can find this cause of the excess oil in those particular cylinders.

ctmccloskey

After re-reading your entire series of posts and it struck me again.

You loose more oil driving at higher speeds, that is a huge hint...It has to be blowing the oil out and for some reason your #2 is the place it chooses. The only way for it to get in the cylinder is around the rings which checked out okay when you did the leak down test or through the valve train. Unless the head is cracked it must be from above the cylinder head. I have both types of seals on my heads, they were cut for the newer style Umbrella seals used lately in addition to the old style seal.

What brand and weight oil do you use? Does the car smoke after starting up, how about when you let off the gas at speed?

Look for where the car is supposed to release the buildup of pressure from inside the block. I mean take it off and verify that it is indeed an open path for the PCV to dump pressure. This is why I suggested checking the PCV valve. Some Engineer came up with the brilliant idea of having the excess air volume leaking past the piston rings be burned off so it would reduce the pollution the car makes. I have seen cars pressurize their engines before but it didn't take long before some seal or whatever lets go.

The faster you drive the worse it pumps out. I am beginning to think that you must have a oil seal issue with your cylinder head. Your leak down test should have shown this by blowing air out of the Umbrella seals. You might upgrade to the later style oil seals if you have not done so already.

The problem might be made worse by a really loose valve guide as it might push the seal up and away so the oil could get in. Loose valve guides are a common issue on light private aircraft with piston engines. A loose valve guide could help explain what you have going on. It certainly can help you use up a lot of oil quickly.

Something is blocked or plugged and after losing that much oil in such a short distance you must be really pouring it out someplace. No drips anywhere? Excess oil consumption is a killer for your Catalytic Converter, don't let it destroy the converter.

Good Luck and please check out that breather line when you have some time! I hope that we can be of help to you, this is a challenging topic.

383vett

ctmccloskey

You are right, I must have been thinking of something else. I apologize. My bad...

How can you test the valve seals on an individual cylinder when it is assembled?

I am not sure about this problem but it is a good one, one question I have is what difference does engine heat play? If the engines was cold and the pistons have not completely expanded out whether the oil consumption is going crazy then or afterwards when the engine is up to normal operating temperatures.

It has to be something dealing with Number 2's sealing of the cylinder. I am still waiting to see if the PCV was closed or stuck. With internal pressure you get problems.

Isn't that why a lot of serious racers use a vacuum pump to help piston rings sealing better?

Thank you 383vette for catching my error, I hope it didn't make it worse for anybody. I use leak down testing on several of my cars and on aircraft, I forgot that this particulars cars Leak downs showed "similar information" to other cylinders. I would love to see the numbers for all the cylinders for comparison sake.

Is there a reason that the cylinder that burns the most oil just happens to be cylinder #2? The leading cylinder on the right side of the engine. Are there any flaws in the original head gaskets? If the gasket was the source of the problem it would be obvious on a proper Leak Down test. What else could go through that volume of oil so quickly?

The only way anything would leak out would be if it had a really bad valve guide that allowed movement and air to leak back around the intake valve. Could a valve stem being worn down a bit or out of spec's do this?

Any ideas out there guys? This a challenging issue!

Good luck and lets help this Gentleman get his Beautiful Corvette back on the road again!
Chris

Corvettes were made to be Driven!

kael

Restate a few bits:
No drips.
No smoke noted at start.
Runs well. I've only driven one C4 though.


Machinist reviewed the heads, 3 valves replaced, rest good. Pretty sure I asked about valve guides, I'd already read those might be the problem. This was January, 2017.
Running Mobil 1, 10-30W.

Winter 2017/2018
Removed/installed intake manifold, gasket leaking.
Replaced injectors.
Replaced PCV valve and hose, I'll re-check it.
Replaced EGR valve. Heard this might be a problem at speed. Plan to run test chart on it soon.

Sorry if I seem short or angry, this sure does bother me. Rebuild means I'm screwed for at least a year or two. Maybe three. Gah!

Last, pics from 2017 when I pulled the heads. Ugh.


#2 valves

#2 piston
Ugh, does this say scewed? I forgot and likely blocked this pic.

Right after removing head.

Prep for head install. I cleaned some more getting rid of the black crap.

confab

You could run the leak down test.. I was under the impression that bad guides or seals resulted in a blue smoke condition at startup?

Ruling out the intake gasket, and given that it is only the one cylinder.. It about HAS to be rings or guides/seals.. Right?

mtwoolford

I assume that really oil caked valve faces are from your # 2 cylinder, but looking at the piston crowns, it looks like all the cylinders, to a greater (mostly greater) or lesser degree suffer excessive oil contamination...and from the cylinder walls, it looks like the engines hasn't any excessive wear.

But with oil consumption like you're having the cylinder walls should be well lubricated !

What I can almost guarantee id that the compression rings are carboned up and not sealing.

I know I'm gonna get flamed for saying this, but you could pull each piston, remove the rings, install a new set of rings; get a glaze breaker, deglaze the cylinder wall, put in a new set of rod bearings and call it good.

Now of course that begs the question, where did the oil come from initially. Well it had to come from some where that all the cylinders were contaminated equally. So, either all the valve stem, valve guides, valve seals are bad;

or there's some path between the crankcase , and the oil in the crankcase, into the intake side of the engine.

if it was a bad intake gasket, or a flaw in the head, I would suspect that the oil / carbon would be more ore less localized around the closest intake runner...not the case.

So the oil has to be coming in somewhere it can be equally distributed.

That could be a pvc issue; which you've probably investigated pretty thoroughly; or

a flaw in the intake manifold itself...this could be a casting flaw; or

when the intake manifolds are machined, in several places, the are drilled all the way through and the portion which is now open to the crankcase is sealed with a plug; I would suspect that maybe one of those plugs on the bottom of the intake has come loose or needs to be resealed...ala JB Weld.

Good luck, but I bet that once you find the source of the oil contamination, you'll probably be able to free up the rings with penetrating oil without doing any further disassembly, and get many more miles of service out of that engine.