The Stovebolt Site Forums The Shop Area Engine Shop 1965 283 Positive Crankcase Ventilation Questions

I have a 1965 C10 with a 283 that I am rebuilding. The engine had one hose from the oil filler neck to the base of the carburator and a second hose from the valve cover to the air cleaner. It also had the original draft tube hole plugged with a rubber grommet. During the process of removing the engine and rebuilding it I found that the bolt that held the draft tube was broken off and I was able to remove the broken bolt so a draft tube could be reinstalled. I want to install the original Chevrolet script valve covers so I need to re-route the hoses used for the positive crankcase ventilation. I did a little research and found that you can install one hose from the oil filler neck to the air cleaner and the second hose from the draft tube to the carburator. Does the PCV Valve need to be installed on the hose from the oil filler neck to the air cleaner or the hose from the draft tube to the carburator or does it matter? Also, is the PCV Valve directional?

Hy bargy1, the pcv valve requires engine vacuum to work so it will have to be plumbed to the carb vacuum source, or manifold vacuum. There was a cone shaped adapter for the road draft tube port on the first pcv equipped 283s, it has a hose fitting on it. The pcv's for those early engines had a 1/4" N.P.T. on one end which screwed into an elbow or a T if the vehicle had power brakes, and yes the valve is directional, hope that helps.

The PCV valve is a one way valve. It allows the carb to suck the fumes out of the crank case keeping the bottom end clean. It blocks any backfire from the carb from igniting the fumes in your crank case, and blowing the pan off.

Larry

Shop Shark, was the elbow with the PCV general screwed directly into the base of the carburator? If so, I might alraedy have the piece. Thanks, Bargy1

yes bargy, the pcv goes in the line from the rear base of the carb to the road draft opening [a fitting replacing the tube] and that sucks the fumes from the crankcase, but there should be a regular vented cap on the oil filler so there's someplace for air into the block - skip the tube from the oil fill to the air cleaner, you do not want to be creating a vacuum in the lifter gallery and oil pan picture of the pcv part - don't know how that original setup will get by inspectors in Calif .... the tube from the valve cover would have been the one into the air cleaner

Bill

Thanks for the info Bill. Sounds like i need to get a breather type oil filler cap and a oil filler neck without the hose barb. The picture really helped.

If you end up using the original road draft tube opening as your pcv valve fitting, make sure you have the oil vapor separator/canister installed in the lifter valley under the manifold. High vacuum without it will suck out oil. Google early SBC PCV images for the various open/closed PCV hose routings from back in the good old days.

SimS

Thanks guys for all the information. I know now what to do!