Posted by Clint Dixon on Thursday, October 23, 2003 at 8:02PM :
In Reply to: PCV valve posted by Tim Holloway on Thursday, October 23, 2003 at 7:48AM :
Most of the 2WD drive vehicles used a "filtered" oil filler tube cap and a road draft tube which attached to the side of the block below the exhaust manifold and next to #6 cylinder. This tube was positioned to point down towards the ground. The idea was that, as the vehicle traveled down the road, air passing by the open end of the draft tube would create a vacuum and suck the crankcase moisture and gasses out through the draft tube and into the atmosphere. The crankcase was repentished with fresh air being sucked in through the oil filler tube cap.
Because the Power-Wagon was intended for use, not only as a truck, but also as a tractor and a portable power plant, one could not always depend upon enough forward speed to create the needed vacuum at the road draft tube. A closed crankcase ventilation system was used instead. This consists of 3 major components: (1) a tube connecting the top of the carbureter to the oil filler tube. An unfiltered oil filler tube cap was used, and the fresh air being sucked into the crankcase was now being filtered by the carburetor's oil bath air cleaner. (2) a tube connecting the open boss on the side of the block, normally used for attachment of the road draft tube, to the intake manifold. Through this, crankcase gasses and moisture are sucked into the manifold and burned in the cylinders. (3) a Donaldson Valve or "PCV valve" mounted inline within the tube between the block and manifold. This valve lets the flow in this tube move in one direction only, towards the manifold.
I am not sure just what all benefits the Donaldson Valve provides, besides the obvious that a backfire can not enter into the crankcase from the intake manifold.
Hope this helps explain things a little.
Clint
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