Thread: pcv???

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what is a pcv like what does it do? where exactly does it fit? and how many per installation? these are really dumb questions but this is the only way i know how to learn...

thanx and appreciate your time

positive crankcase ventilation, usually found on one of the valve covers,will have a 3/8 hose running to a manifold vacume source, main pupose is the feds say we can't vent crankcase fumes to the atmosphere, but the upside is it pulls a slight vacume on the crankcase and keeps crankcase preasure from blowing oil out of seals and gaskets.... one is used but you have to have a breather somewhere with a filter as it has to pull clean air in (usually on the opposite valve cover)......Hope this helps.....

Old Ways,
Mr Worrell explained it pretty, well You should have a breather on one valve cover and the PCV Valve on the other which is usually routed to the base of the Carb. The way it is designed , if all works right , is it draws ambient air in the breather , down thru the valve cover into the crankcase and then the oil vapors are drawn up the opposite valve cover thru the PCV Valve and then burned in the engine and as he stated it was a pollution thing, the PCV Valve is actually a check valve, and since it has oil vapors being pulled thru it they do need periodic maintainance ( cleaning in solvent ) or even replacement. one thing you should not do ,is not have a way for the engine to vent , ie, no breathers as the faster the engine runs the more crankcase pressure it develops due to the crank sloping in the oil at higher RPM's, if this does happen it'll develop enough pressure that somethings got to give and it's usually the weakest gasket or gasket's. It'll blow them out and the oil will follow. usually lot's of it too ! Hope this helps.

Positive Crankcase Ventilation.

piston rings even when brand new have a certian amount of blowby. Which pressurizes the cank case. Without a venting system this pressure will deplete total HP output and cause oil leaks.

So hooked to your carb or intake on the vacuum side is generally a 3/8 rubber hose attached to the PVC valve on one of the valve covers. The pvc unit it's self is a simple one ball valve. When the steel ball feels carb vacuum it opens and allows manifold vacuum to vent the crank case.

Motors actually see a hp increase up to about 20 inches of vacuum. High crankcase vacuum levels are only attained by aftermarket vacuum pump motors or dry sump systems

If you don't mind cluttering up your engine bay a bit you might think of adding a PCV catch can.

Abe