this is weird...oil burning

[goertz]

ok, I've only had the '69 for a week or two now, but a few things have come up that baffle me. Here's the history, #'s matching engine was rebuilt about 1000 miles ago, and stroked to 383. On the 4th of July, we went to watch some fireworks. when we were leaving we were stuck in traffic. at this time, i notice when the other car's headlights hit the car, I could see oil smoke coming from the left side pipe. You can't see it in the daylight, but when headlights hit it, it's REALLY NOTICEABLE, and just seems to do it at idle. If you crack the throttle and clear it out, it stops for a minute or two, then comes back after it idles for a little bit. I was thinking a bad valve seal. But when you start the car, there is NO noticeable smoke on start up, which is typical with bad valve seals. There was a bad lifter in the engine, so I needed to replace that and figured I'd do valve seals at the same time. I did a cooling system pressure test, and a compression test before anything was taken apart, just to be sure. Those tests turned out fine. cooling system holds 15 psi for a half hour or more, all cyls read 180-185 on the compression gage. When I pulled out the #6 plug, it was wet with oil. when you crank it over, you get some oil spraying out of the #6 plug hole. So I pull the intake to do the lifters, and inside the ports of the head and intake on #6 is a brown slime that goes all the way up into the intake manifold. It's obviously the oil that the engine is burning, but where could it be coming from? I wouldn't think valve seals would cause a mess like that to travel UP the intake. Intake gaskets looked ok, not coming in from underneith or anything that I can see. All other ports look dry and fine. Only #6 looks like this. any thoughts?

 

[akfox1]

Look inside the #6 intake port on the head. See if someone got too aggressive with a grinding tool while porting/ polishing the inlet on #6. It wouldn't show up on a compression test either.

Maybe a crack in that area, or a tap sent too deep from previous machining. Just some ideas.

 

[goertz]

Look inside the #6 intake port on the head. See if someone got too aggressive with a grinding tool while porting/ polishing the inlet on #6. It wouldn't show up on a compression test either.

Maybe a crack in that area, or a tap sent too deep from previous machining. Just some ideas.

I thought the same thing. I felt around in there and didn't really feel anything. I think tonight I'll clean it up a little more, and get a good look in there and feel around a little more.

 

[goertz]

OK, I cleaned it all up inside the port, shined a bright ass light in there, felt around and nothing. no cracks, no over zealous porting, no bolt holes exposed etc. the ports are mildly ported only where the intake meets the head for whatever reason. looks like it was just enough to round out casting flash. I tried to wiggle the valve around and it doesn't move. the spring is still on because the heads are still on the motor, but no play at all. tomorrow i'm going to air up the cyl, and pull the valve spring and check the stem seals. I've seen motors with leaky stem seals before, but nothing that ever made the ports on the head and intake manifold look like this.

 

[black_81_vette]

Ok I have a question for you.Where does the vaccume line originate from for the PCV Valve? If it is on the port for that particular cylender that may be your problem. I have seen faulty PCV Valves suck oil right out of the engine. Also I dont know what valve covers you are running but some do not have the oil air seperator in them. I would check that too while your in there. Its also quite possible you had a intake gasket leak even though it diddnt look like it from the gasket try using a thin coat of Gaskesinch on them when you reinstall the intake.

 

[74bigblock]

What kind of carb? Sounds more like a rich idle condition on that side of motor. If it only does it at idle at temp... me thinks there isn't anything wrong with your motor. I would think any valve train issues would get worse as RPM increases. Your issue goes away as soon as you touch the gas.

 

[akfox1]

Where does the vaccume line originate from for the PCV Valve? If it is on the port for that particular cylender that may be your problem. I have seen faulty PCV Valves suck oil right out of the engine. Also I dont know what valve covers you are running but some do not have the oil air seperator in them.

I like this explanation too. I thought about this last night, but I didn't look up which cylinder is #6?

 

[goertz]

yeah, but only the #6 cyl port is caked with muck. It's an engine issue for sure. the other 7 plugs all look excellent. I'm running a carter carb on an edelbrock manifold. the #6 cyl is sucking major oil from somewhere, and it's not likely the rings, because compression is excellent.

 

[goertz]

thought of it too, no dice. the pcv goes right into the carb. I would think if this were happening, all the cyls would be uniformly crappy. it has the tall valve covers on it, with the oil shield on the breather and pcv holes. I'm hoping it was coming in through the intake gasket, but I would really like to find the "smoking gun" before I button it back up.

 

[jdp6000]

How about through one of the bolts? Did you put thread lock on them?

Jim

 

[WayneLBurnham]

How about a previous leak on the intake gasket - on that port

only, causing it to pull oil out of the valley into #6? The center ones are always the worst for leaks, and, if it's underneath and there is otherwise a good seal on intake and the valve covers are tight and hold vacuum and such, it often isn't that easy to find. At least it's not TOO hard to test,a s you only have to put the intake back on and fire it back up after the sealant dries....

Now you did say there is oil ON the outside of the header too, huh? THAT could be a totally different thing - a leak from the bottom outter corner of the v-cover on that side, the rear of the intake or even the oil sender (although that's odd for it to be on that side.)

I had a substantial leak that was my own idiotic fault - from the TC!

 

[goertz]

the oil on the outside of the header was from doing a compression test with all the plugs out. #6 puked all the oil out when it was cranking. I don't think there has been a previous intake gasket on this since the motor was built, and the oil that it's burning through there is fresh. I'm hoping the new gasket and valve seals stops it. we'll see soon enough.

 

[black_81_vette]

Ok since the PCV is not the issue I have something else to look at.I had a 66 corvair once, now that I thought about it did the same exact thing your corvette now does.I had perfect compression in all of the cylenders wich too had me baffled.Like you I had a spark plug that was wet with oil. The only real main difference between the problem you have and the one I had would be the oil in the intake.My trouble ended up being a broken expander ring on the oil ring assembly. It could be a bad oil ring or improperly installed oil ring assembly, but the oil in the intake sure suggests a leak into the engine where it could pull over oil into the port.I would make sure the angle of the intake matches the heads,there is a possibility the intake was milled or vice versa causing a slight missalighnment the gasket couldent take up.its worth a shot, and while your in there it wouldnt be a bad ideal to maybe pull that piston out and check it out just for peace of mind.The worse thing could be a cracked pistion skirt ect.It would be better to find out what it is and fix it than not being able to sleep worring about it.

 

[goertz]

it could be the heads were milled, and it's just a little bit off from the manifold. i'm going to reinstall it all, put a very thin film of sealer around the ports, and tighten her down. the intake bolts were't loose when I took them off, but it seemed like they could be a little tighter. If that doesn't do it, i'll look to the valve seals. I just can't see it coming up from the bottom end like a bad ring. being how far it is into the intake, I'm leaning toward gasket not sealing. Although typically, you would see some stains on the intake, the head, or gasket where it came through. we shall see this weekend what happens.

 

[mrvette]

The man with the suggestion of angle milled heads is right on, I had similar but worse issues with this 355 engine some years ago...had the intake milled to knock off 20 mills from the top edges on both sides....that fixed it....but I had a uniform oil burning pattern, all cylinders had oily intake passages....

GENE