C2 Crankcase ventilation

[John Luca]

Here's my problem:

I have a 1965 327 cu. in. 350 HP Corvette. It has a "closed positive" crankcase ventilation system with a metered orifice connection at the Holley 4150 carburetor which goes through a rubber hose to the oil fill tube.
There is no PCV value tn this system and the oil fill tube is closed off with no ventilation. There is also another larger tube (approx. 1") that goes from the rear of the engine block (near the oil pressure line) to the base of the air cleaner which is at
tached to the spark arrestor.

My problem is that the engine is pushing oil up through the spark arrestor into the carburetor and the air cleaner. The car runs excellent, but something is definitely wrong. As an experiment, I wanted to see if the oil was being sucked up, or pushed up through the tube, so I temporiarily closed off the tube at the spark arrestor. Well, it didn't like that at all...there was oil all over the rear of the engine. I checked the metered orifice and it is clean and open.

The only thing I can think of is that there is something missing on the engine side of the tube that is supposed to prevent oil from coming up through the tube. Any help would be greatly appreciated.

John

[Wally Knight]

Re: C2 Crankcase ventilation

I would have thought a 65 small block would have a road draft tube and not a connection to the air cleaner? Anyway, there is a canister in the lifter galley that is supposed to prevent a major amount of oil from escaping the inside of the engine. If it is clogged or not there at all you will have oil control problems.

I don't know if these are available in the aftermarket world but I think you can clean them and put it back. It's a pain in the butt to do, intake nees to come off, so much fun leaning over the fenders!

[Wally Knight]

Re: C2 Crankcase ventilation

I would have thought a 65 small block would have a road draft tube and not a connection to the air cleaner? Anyway, there is a canister in the lifter galley that is supposed to prevent a major amount of oil from escaping the inside of the engine. If it is clogged or not there at all you will have oil control problems.

I don't know if these are available in the aftermarket world but I think you can clean them and put it back. It's a pain in the butt to do, intake nees to come off, so much fun leaning over the fenders!

[Bill Clupper]

Re: C2 Crankcase ventilation

There is an oil seperator in the valley of the engine below the intake manifold to keep oil from backing up into the tube to the air cleaner, but I'm mistified by your description of the oil fill tube as a "closed tube". The oil fill tube should have a fitting for the rubber hose to connect to that comes from the metered orafice on the carb. The proper flow is theat the large hose from the air cleaner flows air into the crankcase that provides makeup air for the vapors that are pulled off via the constant vacuum source at the carb. If this is hooked up and you are still pumping large quantities of vapor out of the large tube, a look at the overall condition of the engine might be in order via a leakdown test. I was working on my '65 300hp yesterday, and there was virtually nothing coming up the hose at idle or if you "Blip" the throttle.

[Bill Clupper]

Re: C2 Crankcase ventilation

There is an oil seperator in the valley of the engine below the intake manifold to keep oil from backing up into the tube to the air cleaner, but I'm mistified by your description of the oil fill tube as a "closed tube". The oil fill tube should have a fitting for the rubber hose to connect to that comes from the metered orafice on the carb. The proper flow is theat the large hose from the air cleaner flows air into the crankcase that provides makeup air for the vapors that are pulled off via the constant vacuum source at the carb. If this is hooked up and you are still pumping large quantities of vapor out of the large tube, a look at the overall condition of the engine might be in order via a leakdown test. I was working on my '65 300hp yesterday, and there was virtually nothing coming up the hose at idle or if you "Blip" the throttle.

[John H.]

Re: C2 Crankcase ventilation

You might also make sure that the rubber hose from the oil fill tube to the orifice fitting on the carb is clear and is passing vapors; they deteriorate just like brake flex hoses (swell internally and restrict/block airflow). Also make sure the opening is clear where the hose nipple is attached to the oil fill tube. If all the hoses/fittings/orifices are clear, you may simply have more crankcase pressure than the system can deal with due to excessive blow-by and it's backing up through the (intake) tube/hose to the air cleaner, as the other end of the system is only a .090" orifice in the fitting at the carb air horn.

[John H.]

Re: C2 Crankcase ventilation

You might also make sure that the rubber hose from the oil fill tube to the orifice fitting on the carb is clear and is passing vapors; they deteriorate just like brake flex hoses (swell internally and restrict/block airflow). Also make sure the opening is clear where the hose nipple is attached to the oil fill tube. If all the hoses/fittings/orifices are clear, you may simply have more crankcase pressure than the system can deal with due to excessive blow-by and it's backing up through the (intake) tube/hose to the air cleaner, as the other end of the system is only a .090" orifice in the fitting at the carb air horn.