installing a pcv in my flathead.

[grey beard]

Ken Bartz,

You have the righr general idea there, with a few exceptions. Engine vacuum pulls a constant negative pressure on the crankcase via the PCV valve, keeping all contaminants, combustion byproducts and mostly condensation out of the crankcase where they would otherwise prodce sludge.

Where the oil fill tube comes in is that with the pcv system pulling a vacuum on the crankcase all the time, there must be a source for clean air to enter to replace what is being pulled out. The stock oil fill cap with a small filter in it could be used, but is not a truly reliable air filter for a pcv system It worked okay for the road draft tube, because not much air passed that way, and a quick wash out with parts cleaner each oil change kept it clean. With a pcv system, a constant stream of air is moving through the crankcase, creating a need for a constant source of clean, filtered air. My oil fill tube has a spingloaded flap on top and a hose fitting on the side. From this fitting a hose pulls clean air out of the air filter body on the engine intake to supply fresh crankcase air. All newer engines have used this type crankcase ventillation system since the early sixties, so this is nothing very new - just a whale of a lot better than a road draft tube. JMHO:)

(See pics of my B1B PCV system in a sister thread above this one.)

[Shifticus]

The pcv setup in the '54 I recently posted. The hose routes to a fitting threaded into the intake manifold. Does it work? I'm not sure..

[De Soto Frank]

I'd like to suggest the following:

1) "Smoke billowing out the oil filler / breather pipe before you rebuilt the engine" - this was due to worn rings and blow-by.

2) "Fan creating air-flow" - Well, maybe; I can't say that I've laid under my De Soto next to where the "road draft tube" would end, to see if there's any breeze down there from the cooling fan at idle... I guess the air getting pulled through the radiator has to go somewhere... and I guess that would be down under the floorboards, providing all splash-aprons are installed.

The old open breather system worked best out on the open road, at speeds above 30 MPH.

My '41 De Soto came from the factory with a PCV system. Instead of the "road draft tube" (breather pipe) under the exhaust manifold, there is a pot-metal cap & valve bolted to the port in the block, which has a 5/16" steel line running up behind the end of the manifold, to a double-wide 5/16" female inverse flare to single male 1/8" NPT block, which threads into the intake manifold. The other 5/16" female IVF is for the vacuum wiper connection. On the oil breather/filler pipe behind the generator is the regular breather cap with the metal filter mesh.

Inside that pot-metal cap is a sort of floating weight valve gizmo that is supposed to repsond to intake vacuum. I believe the principle is the same as modern (post 1963) PCV valves: when intake vacuum is low (hard pulls), the weight drops, opening the valve and drawing-off blow-by. When the vacuum comes back up, the weight is sucked-up and mostly closes-off the valve, now creating a gentle "bleed" to scavenge vapors off the crankcase, w/o causing such a vacuum leak as to destroy smooth idling and fuel economy.

I think we would still see crankase vapor from our modern cars, except they run any fresh-air vent into the air-cleaner system, so that nothing but tail-pipe emissions can escape to the atmosphere. I've pulled the oil filler cap on some of my modern iron while running, and seen a steady stream of "smoke" exit the valve cover...

One other fellow locally has a '41 De Soto, and his car originally had the factory PCV system. He said "it was a gas-waster" and he removed it and put on the regular road draft tube.

I am suspicious that the valve on mine is not particularly effective, and I have been thinking about removing the weight from inside the original valve body, and making up a new metal line, fabricated so as to "hide" a modern (readily available) PCV valve bewteen the engine and the firewall.

I have also considered temporarily disconnecting and plugging the PCV port at that junction block on the intake, and seeing if the wiper performance improves any...

In any case, whether the vehicle has PCV or not, short-trip driving, the kind where the engine is always running rich and never gets the oil heated-up to 180 deg F or better for at least 10 minutes, is bad for the engine; this is what causes condensation in the crankcase, crancase dilution, and acid-build-up in the oil. It also shortens the lifespan of the exhaust system, due to internal moisture not getting burned-out.

PCV was one of the first emissions-control systems to be applied to American cars - to cut-down on the amount of un-burned hydrocarbons being pumped into the atmosphere as crankcase vapor from blow-by.

De Soto Frank