I just purchased a 1966 L-79 which was restored and rebuilt in 2002. The engine has had only a few thousand miles since the rebuild. During the trip home, about 700 miles, the car used 2 quarts of oil and began to run a little rough near the end of the trip. When I got home, I removed the air cleaner cover and found oil under the lid, on the bottom half of the cleaner, on the air filter mesh, and under the filter element. The oil appears to have come from the flame arrestor since it was quite wet with oil. Is this situation normal for a PCV configuration like this, or is something wrong? Is this possibly the cause of the rougher idle and running? Any ideas where to start?
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Re: L79 Oil in Air Cleaner
A quart of oil every 350 miles and oil in the air cleaner is certainly not normal.
Start by verifying the configuration of the PCV system with the CSM or AIM.
I don't think one in a hundred "engine builders" understand PCV systems, so they often get ignored or bubbaed up.
Duke -
Re: L79 Oil in Air Cleaner
I checked the PCV valve it is: "TYPE C.V.-726 C" it is clean and rattles as it should. It screws into the side of the chrome oil fill tube. Oil fill cap is a repro. chrome non-vented cap. I am not sure what else to check in the system, for that matter, I don't exactly understand the system entirely.Comment
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Re: L79 Oil in Air Cleaner
"I don't exactly understand the system entirely."
Most guys don't. The PCV system should have a fresh air inlet. On my '63 it is a hose from the downstream side of the air filter to a nipple on the oil fill tube.
This filtered fresh air is drawn into the crankcase by manifold vacuum where it is mixed with blowby and drawn out the back of the block through a tube that leads to the PCV valve on the back of the AFB which is exposed to manifold vacuum. The valve meters flow based on manifold vacuum. High vacuum causes the valve to restrict flow, so it doesn't suck the crankcase dry.
I believe the flow on your system is reversed - air is drawn from the air cleaner to the entry at the back of the block next to the distributor and out the oil fill tube to the valve, which should connect to a vacuum port somewhere on the carb or manifold.
I don't have a '66 AIM or CSM, which is what you need to understand the specific configuration of your system. Owners who don't have such basic service documentation should just lock their card in a garage and never touch them.
Clean the valve in mineral spirits, dry it, and then use a small screwdriver to press on the valve to be sure the spring is still functioning. You can also use oral vacuum to verify that the valve restricts flow as vacuum increases.
Blow through all the hoses and tubes to be sure they are not clogged or otherwise restricted.
Given the oil consumption and oil in the air cleaner, the engine may have a signficant ring sealing problem. A compression or leak down test is in order.
AFAIK the VV726C is a functionally correct valve for your engine.
DukeComment
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Re: L79 Oil in Air Cleaner
Thanks,
Only owned the car since Friday - '66 CSM was ordered upon return home - So I will have more resources next week. I will check out the PCV operation tomorrow. As far a ring sealing problem - I did notice very slight oil sheen image on rear bumpers after driving 700 miles. It was very minor - no where equalling a drop for both bumpers. I don't see any blue smoke, and I have owned a few 1960's oil burners in the past. Keep you posted.
AlComment
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Re: L79 Oil in Air Cleaner
Al, you might pick up a PCV tester. This one cost me one dollar. Pat
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Pic
Just to put what Duke described into a visual perspective, here is a pic. You can see the oil fill tube with PCV on the left and the crankcase vent on the right.Comment
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Another Pic
Here is the PCV and the hose connection on the carb.Comment
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Re: L79 Oil in Air Cleaner
Unfortunately when someone says an engine was recently rebuilt, it can mean anything (not to knock farmers but when they say it I usually run and hide). I would make sure the PCV valve is functioning as intended and make sure you have a closed system that isn't blocked somewhere (as already suggested). The system is pretty basic...filtered air that has come through the air cleaner gets drawn down into the engine under negative pressure (that one picture in this thread shows a big hose running from the under side of the air-cleaner to the valve cover). Once inside the crank-case, this air combines with all the nasty gasses and gets sucked out through the PCV and into the base of the carburator and burned in the engine. It increases engine life and reduces emissions. Those gases are very acidic and kill the engine over time. Before the PCV system came along, engines just used a simple down-draft tube. The oil cap used a wire mesh filter thingy and as you drove down the rode it sort of naturally sucked out the underside of the engine. The down draft tube usually ran out the back of the engine and slanted towards the rear of the car. When I was a kid I would always look at that down draft tube from the underside of the care and wonder what the hell is that thing for?? If the PCV system checks out OK, I would do a compression check and maybe check the valve adjustment. You might let the seller know what is going on and ask him if he has a suggestion?? Good luck, TerryComment
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Re: L79 Oil in Air Cleaner
Well, I removed the PCV valve. Spring appeared operational. I cleaned it in mineral spriits, dried it out. Oral vacuum did open the valve. Confirmed that it sealed properly in other direction. Checked the hose - it was clear, pinch clamp at carb/manifold side was not real tight, so I moved it closer. Reinstalled PCV with a little teflon tape for a better seal. Wiped up all the oil in the air cleaner area. Will test drive this afternoon. Also monitoring oil consumption.
Thanks for all the advise, will keep you posted.
ALComment
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Re: L79 Oil in Air Cleaner
Just went for a 15 minute test drive. Checked to see that system was working by looking for air going into the flame arrestor tube. At idle, it was pulling a tissue to the screen. Went for a ride - engine runs a bit rough when accelerating from idle speed. Smooths out with more gas. After return, lots of oil and foam under the air cleaner lid. Pulled off the air cleaner unit and stuck my finger into the flame arrestor tube. Dry. No oil. If the PCV valve/system is working, how is the oil getting into the air cleaner?Comment
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Re: L79 Oil in Air Cleaner
Al,
Just an amateur but I would suggest that you have an oil ring problem.Comment
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Re: L79 Oil in Air Cleaner
Hi Al, Hope I don't give you bad news but I had that same problem with a 1978 Pontiac 301 cu.in. motor in a Grand Prix. I had purchased the low mileage car from my freind, and when I went to do a tune up on it I found the same problem you have. The breathing of the motor is going in a reverse direction which usually means "RING PROBLEM" lower engine "HEADACHE". As soon as I had this problem with my car, consider it gone. Hopefully you can get some answers from the seller, because that's a nice year vette and I'd hate to have to pull the motor and endure the costs. Maybe the seller will help you out. Best to ya. Ken.Comment
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Re: L79 Oil in Air Cleaner
Leave the lid off the air cleaner and rev the engine. You should see where it is coming from. Block the wheels and all that stuff. I bet you will see it spitting out the flame arrestor. TerryComment
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Re: L79 Oil in Air Cleaner
I warmed up the engine, took off the air cleaner lid and brought the RPM to 3500 several times and 2500, etc. I did not see anything comming from the flame arrestor screen. At idle, the PCV valve was chattering. I removed the hose from the carb side of the valve and confirmed that there was strong engine vacuum. A few seconds after I did this I saw a mist coming from the flame arrestor. Possibly oil mist. The flow was definitely reversed with the PCV hose disconnected and the engine at idle. There is no elbow into the base of the carb - it is a straight fitting. I stuck a wire in about 6 inches and it came back with a few spots of oil on it. There is vacuum at the top of the oil fill tube with the non-vented cap off. The vacuum get a bit stronger at higher RPM. Is it possible that the direction is reversed only under load (actual driving)? Seller said they did a compression test and all cyls checked out.Comment
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