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wtf...oil blows out breather a14


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If it's blowing out of the breather, chances are, the PCV isn't even hooked up.


Oil can "blow out of the breather" if the rings are not working properly and the crankcase is being pressurized by compression. It can also happen at high RPMs in any motor.


On some engines, I use a cheater PCV system. A PCV is essentially a vacuum leak, so I don't always like to run them, but I will plumb the valve cover and block breathers together in a tee and then run that to the air cleaner. The small amount of vacuum created in the air cleaner is usually enough to pull a vacuum in the cranckase and eliminates the blowing breather scenario, and the bonus is that I don't have to tune the carb around a vacuum leak (PCV).

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The PVD is a metered orifice in the intake. This 'leak' is countered by the carb or included in the design. Most N Am engines from '62 have a PCV system.


The PCV is under varying vacuum depending on engine load. It will draw fumes most on deceleration and next most at idle. As engine load increases, the manifold vacuum decreases, and at WOT it is extremely low.  Unfortunately blow-by past the rings increases with engine load so the PCV is quickly overpowered. Excess blow-by is directed out the valve cover to the air horn on the carb where suction draws it in.


Now, oil spewing out of the valve cover hose indicates a sudden increase in blow-by, enough to push oil fog droplets through the valve cover baffles and out. 


Blow-by is usually from combustion pressure not contained by worn out rings. It can also be from a hole in the piston and/or damaged ring lands.   

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