BNS engine crankcase pressure - what shoul it be?

[ven0m]

When the engine idles and you remove the oil filler cap. What pressure should be at the opening? Positive (blow out), negative (suction) or neutral?

[ven0m]

Anybody?

[GaretS4]

That is an interesting question. I think that it should be positive. Some gasses escape past the valve guides and create a positive pressure in the top of the engine. The crank case and oil sump are the areas of the engine were positive pressure is the largest due to exposure to the combustion gasses escaping past the rings (referred to as blow-by) as well as volatile gases from hot oil within the sump and rest of the engine. Therefore the need for a crankcase ventilation system, otherwise the excess pressure will blow out crankcase seals, among others. I'm not sure if the top and bottom air spaces of the 4.2 V8 is are connected, but I think that they should be or else excess pressure in the valve cover area could blow out the valve cover seals.
Garet

[Quattrors4]

negative ,-1.5hg so vacuum