zuendler

Got a question, but a story behind it:

Have a new zz502 in my C3 since 5000 miles now, and it burns 3qts of oil on 1000 miles.
To ensure its not going trough the PCV I put a restrictor in the hose, that limits the diameter to 1mm.
But oil consumption did not change.
I switched from 10w40 to 20w50 without improvement.

I found many threads about 502īs burning oil in the internet, the related it to the low tension rings.

So I had a look inside the cylinders, but didnīt see anything unusual.
Despite a lot of oil-cole on the pistons.

So I removed the carburetors to have a look on the intake valves.
The valves have a lot of oil-cole on them! They look like exhaust valves.
I found also oily surface in the intake manifold.
I donīt know if this is quite normal or not.
Is a bit oil there normal or not?

While the normal zz502 has no breather on the driver side and just a PCV on passenger side, I have put the base L71 system on it.
With the thick hose on the driver side valve cover:



There were some drops of oil on the flame arrestor in the air cleaner housing, but the hose it self was completly dry inside.

I have disassembled the hose from the air cleaner now to see what happens. If the oil doesnīt come from here or from the PCV it must come from the valve shafts.
Experiences?

zuendler

Here is an intake valve with the black $hit on it



thats not how an intake valve should look like hm?

and the manifold:

jackwabbit703

I don't think burning 3QTs of oil is never good at 1K miles.

Too much oil pressure or too much oil?

BAD *** MOTOR BTW!!

CheezMoe

Hello zuendler, It sounds like the intake manifold gasket may not be sealed properly and sucking oil from the lifter valley into the intake runners. This would also cause a vacuum leak. Was it running good otherwise? I imagine burning that much oil it would be hard to really tell. I suggest to clean it up real good and replace the manifold gasket, and be sure it does not slip down when you set the manifold. Glueing the gasket to the head might be required here. Good luck!

CaseyJones

I agree with this one. Unless you are running a cam with a BUNCH of overlap AND the rings are really loose the intake valve and the intake itself should be pretty clean. If the rings are so low tension that you burn that much oil you would also have a high crankcase internal pressure pushing significant oil residue out through the PCV system.

Super6

Are the rocker studs/bolts on the intake valves sealed at the threads?

zuendler

Ok, current setup: PCV blocked, hose of driver side valve cover disconneted from the air cleaner and let it just open.

- now I have a nice smell in the car
- intake is oilfree inside
- oil consumption dropped to 1qt / 1000mls

So I guess it was not the intake to head gasket.

zwede

Two things you should check next:

1) Does the valve cover where the PCV valve goes have oil baffles? And also what kind of baffles are they?

2) What PCV valve are you running? They are not all the same. You could try a PCV valve that flows less, such as one from a 4 cyl Chevy S10.

zuendler

I have the old original GM chrome covers and they have a sheet inside under the PCV.
Previously I used the PCV that came with the zz502. Later I had a 1mm restrictor in the hose - without any positive result.

Disconnecting the hose to the air cleaner made the big difference now.

zwede

The restrictor will not work. You need full vacuum at the valve so it closes. If you put a restrictor in the line the PCV will be wide open and though it is counter-intuitive, it will flow more during conditions where flow should be low (such as cruise and decel).

I've heard the PCV should be in the driver's side valve cover and vent on the pass side due to the rotation of the crank. I noticed yours is the other way around. Don't know how much of a difference that makes.

maverickmk

I would think if you're "burning" 3 quarts of oil every 1,000 miles you would have blue smoke just rolling out the exhaust. Are you sure there isn't a leak somewhere? That is a tremendous amount of oil to be burning.

gdh

I had this situation not long ago, was going through 1 quart every 400 miles. My engine was built initially to run 1/4s so with the ring tolerances and types I was told that I would have more blowby than a regular build. I had oil all over the top of the engine, pooling on the intake after cruises but no one every said that I appeared to be burning much oil when they were behind me on a cruise.
I cleaned the engine as best I could a few months ago, tightened down every bolt on the I take, valve covers, heads and headers. In over 1000 miles I have lost maybe 1/4 cup of oil. This engine now has 30k miles on it since the rebuild.
I don't know much about these ZZ502's but I still think that you have a vacuum leak as others have said. With those rings and their inherent blowby you will have an oil coating in your carb as the vent tube goes from your valve cover through the base of your air cleaner to be sucked through the carb and burnt off.

Super6

The big hose going to the air cleaner is used as a source of dry filtered air that will be drawn into the driver's valve cover and through the crankcase/valley side of the engine and then sucked through the PCV valve and then into the intake manifold either through a connection on the intake directly or on the base of one of the carbs. The big rubber hose (and the carb) should not really have any oil in it since the flow is from the air filter into the driver-side valve cover.

zuendler

Ok, last night I took the intake off.
And found no leaks. All valves are looking terrible like in the picture above (how to clean them if I dont want to remove the heads?).
Found some more oil in the lower plane of the intake.

So I think the oil must come through the big hose, because I had disconnected the PCV.
The big hose was mounted to the aircleaner with a pipe in which I had drilled many holes.
So it should not be possible that vacuum is sucking at the hose, but gases coming out of the hose would be sucked into the carb. (Had oil smell during driving anyway)
I found some oil drops in the air cleaner next to the big hose. Im now sure it came this way.

The best results I had was when I had disconnected the PCV and sealed the big hose with a rag. Then I was at 1qt / 1000 miles.

So I guess the engine is producing much blow by. Whats your opinion? And what can I do?

Super6

If you disconnected the PCV then there was no vacuum applied to the crankcase and other internal areas of the engine, so when you would rev up the engine the pressure in the inside would build up due to a combination of blow-by and the agitation effect of the crank and rod motion. With no other way out, the oil mist and gases are going up the big hose and into the engine compartment or into the air filter if the hose is hooked to the air cleaner base connection. This is the same thing that happens if you have open breathers on your valve covers and you put some rpm into the engine.

What I'm getting at is that I don't think you can say that the oil was always going up the big breather hose into the engine. When the PCV was hooked up, probably not or to a much lesser extent.



The picture above is of my 468 with a Moroso Air-Oil Mist Separator installed between the PCV and my intake. I thought I was taking care of the oil-in-the-intake problem with this arrangement. Right until I put the car on the chassis dyno and saw a ton of blue smoke out of the side-pipes on my brand new engine every time the operator let off the gas after a run. The problem was that the intake valve rocker stud mounting holes on the number 1, 4, 5 and 8 cylinders go into the intake runners and they were not sealed, even though the engine builder did put some sealant on the stud threads. I have the exact same GMPP oval port 110cc heads that you have on your 502. And I just went out and looked at them as they are disassembled right now.

My mechanic friend with the same heads was aware of this problem and sealed the threads on his heads and thought that the problem was solved, until he also had his car on a chassis dyno and saw the same thing I did, but to a lesser extent. He went back and used Teflon tape and permatex sealer on the stud threads and on a subsequent dyno run, he could see that he had solved the problem. I have the videos. The point here is that even knowing that these intake studs needed to be sealed, it took my friend 2 shots at it.

Whether this is your whole problem I don't know. But I think it's worth taking a look at.

zuendler

Thank you, this is a valuable information. I will have a look for that.
Did you have a look on the intake valves, to see if the ones with the leaking stud holes are looking worse than the others?
Because my 8 valves are all looking similar bad. I would think only the one where the leak is should look bad.
My mechanic thinks the intake gasket was leaking at one point, caused by backfire. Well, Iīm not sure, for me the gasket looked alright. But he has a lot more experience with this stuff.

Last night I put the intake back on the engine, now waiting for other parts to arrive.

Super6

If you have an oil leak in one runner, will the resulting oil just go to just the corresponding intake valve? That's an interesting question. And hard to answer, at least for me. Even on a large cam, the intake is closed more than it is open and the flow is in pulses, not always flowing into the runner.

I'm on shaky ground with these next few sentences in connection to an oil leak. It is a fact that a dual plane manifold will have better vacuum than a single plane at idle. It has to do with the intake charge being diluted by exhaust gases. Think about a single plane manifold with a common plenum. While one cylinder may be on the intake stroke and it's exhaust valve is closed, adjacent valves can be in an overlap phase where both valves are open and with the result that some of this diluted mixture ends up in the first cylinder, so the engine doesn't run as well. A lot of this problem is solved by using a dual plane manifold, where there are essentially 2 intake plenums and any one cylinder is exposed to the exhaust dilution coming from only 3 other cylinders at overlap, instead of 7. If what was happening in one intake runner didn't affect the others, you wouldn't see this difference in idle vacuum between a single plane and a dual plane. That tends to say that oil coming into the manifold in one runner may end up in other places in the intake.

How are your valve guides? The GMPP heads on your engine are made by Edelbrock. I have a set of Edelbrock heads that only had about 1500 miles on them and I could wobble the exhaust valves. I took a video and there's no doubt that there is more clearance than there should be. The intakes were not as bad. I just had bronze liners installed.

You mentioned low tension piston rings. Would a cylinder leak-down test show a problem there? Aren't you supposed to do the test and then squirt some oil in the low cylinders to help seal the rings and if the low readings get better, it not the valves, but the rings? I haven't seen this test done, so I'm not sure. When you're reading about 502s using oil, what's the solution? Changing the rings?

I'm going to try the 4 cylinder S10 PCV in mine and like I said, I have a separator in the PCV system. You might try those 2 things to start. And a leak-down test.

zwede

Interesting info about the rocker studs. Thanks. I also have those same Edelbrock heads. I have oil on #3 and #5. I used sealer on the studs, but maybe not enough. I'll go ahead and re-seal those studs and see what happens. Probably do all of them just in case oil travels between cylinders.

zuendler

Tonight I pulled all stud rods of the intake valves. And ALL of them end in an intake runner!
The rods were glued with a grey substance, but I think somehow it was not really proof.
Because I found oil in the upper half of all threads and there is a step at the end of the thread: on many of them there were pure oil drops:



So I think its possible that the oil came through the threads of the rods, although they were glued into the heads.

No I sealed them with teflon tape and thread sealer, hoping it will suffer...
(Maybe glueing them with loctite would have been better?)

Super6

Mr. Z,

I'm glad you found what may be the problem, but I have to say I'm surprised that all of the intake bosses were through-drilled. On my set only the 1st and 3rd on the driver's head and the 2nd and fourth on the passenger side (same holes from left to right) were drilled into the passage. I'm glad you were diligent and found that all of yours were drilled. I would have felt bad about that later. Don't know why they are different. I had mine since about 2004, apparently they changed in the meantime. I certainly hope that solves the problem.

I sealed mine, but I'm still going with my oil separator and the 4 cylinder S10 PCV valve.