PCV and breather

[MilkyNoSugar]

I am not convinced the PCV valve and oil filler/breather are connected correctly on my big block engine. The car has non-standard valve covers with the filler cap and PCV valve on opposite sides where the originals would be as far as I can tell.

On the driver-side valve cover, the oil filler cap is a vented cap. I do not believe this is standard as it touches the air intake pipe and the air filter has to be removed to refill the oil. I think that should actually be a cap with a pipe attached and the pipe running to the air filter base plate where the PCV valve is currently connected.

I have a PCV valve on the passenger side valve cover. The pipe from that goes into the back of the air filter housing. I think the PCV pipe should be connected to the carb base plate or intake manifold - on the limits of my understanding but potentially an issue with the vacuum or pressure not being there to control the PCV if it is vented to fresh air effectively via the air filter. I believe the original PCV location would have been on the driver side, and would have connected to the pipe near the alternator where the two jubilee clips are.

Thoughts on that please from anyone who actually understands this?

 

[Oneball]

Yep you’re correct the PCV valve should go to manifold vacuum.

It didn’t matter too much if the other rocker uses a vented and filtered cap or has a tube going to the air cleaner either way it can get filtered air.

 

[MilkyNoSugar]

I have not actually looked at the viability of this, but wonder if it makes sense to swap the cover around to get the PCV port closer to where it needs to tap into the hose, and get the breather closer to the port on the back of the air filter?

 

[Roscobbc]

My earlier ('68) big block has a 'open' air filter and the PCV valve was fitted either within the drivers side cap or 'in-line' in the rubber hose connected to the cap which is then connected to the inlet manifold base behind the carb (or a multi barb full manifold vacuum point) - the passenger side filler cap is connected to a barb underside the air filter base plate. The logic being that the PCV valve aided by a light vacuum will open and allow crankcase fumes to be sucked into the inlet manifold and burnt. This will create negative pressure within the crankcase which in turn is equalised by the passenger side vent tube drawing 'clean' air (via the air filter) into the crankcase to balance internal air pressure. It is important the connections are on the correct sides as the engine rotation also has an effect of how they operate.
In the situation where the engine develops abnormal and excessive internal crankcase pressure (say from broken piston rings) the vent pipe willalso funnel the excess fumes into the air filter to be burnt by the engine and try minimise emissions. If the PCV valve rattles when you shake it, generally its working ok. Replacements are specific for various engines.

 

[MilkyNoSugar]

My earlier ('68) big block has a 'open' air filter and the PCV valve was fitted either within the drivers side cap or 'in-line' in the rubber hose connected to the cap which is then connected to the inlet manifold base behind the carb (or a multi barb full manifold vacuum point) - the passenger side filler cap is connected to a barb underside the air filter base plate. The logic being that the PCV valve aided by a light vacuum will open and allow crankcase fumes to be sucked into the inlet manifold and burnt. This will create negative pressure within the crankcase which in turn is equalised by the passenger side vent tube drawing 'clean' air (via the air filter) into the crankcase to balance internal air pressure. It is important the connections are on the correct sides as the engine rotation also has an effect of how they operate.
In the situation where the engine develops abnormal and excessive internal crankcase pressure (say from broken piston rings) the vent pipe willalso funnel the excess fumes into the air filter to be burnt by the engine and try minimise emissions. If the PCV valve rattles when you shake it, generally its working ok. Replacements are specific for various engines.

Thanks for replying. So if the PCV and breather need to be on the correct side to match engine rotation, are the ones on my car on the wrong sides then - it seems they are??

 

[MilkyNoSugar]

Yep you’re correct the PCV valve should go to manifold vacuum.

It didn’t matter too much if the other rocker uses a vented and filtered cap or has a tube going to the air cleaner either way it can get filtered air.

thanks for replying

 

[Oneball]

Thanks for replying. So if the PCV and breather need to be on the correct side to match engine rotation, are the ones on my car on the wrong sides then - it seems they are??

Doesn’t matter which side they’re on. Engine rotation isn’t relevant. Put them on which ever side works best for pipe routing and access.

 

[Roscobbc]

Doesn’t matter which side they’re on. Engine rotation isn’t relevant. Put them on which ever side works best for pipe routing and access.

Correct 'sided' placement of respective 'caps' is simply good OEM practice Tim. Admittedly more relevant certainly on higher powered engines perhaps without oil pan 'trap baffles' where oil levels, oil droplets and oil mist within the engine will be biased to the passenger side of the engine block due to clockwise direction and resultant 'windage' caused by the rotating assembly, especially at higher RPM's . This can be particulary noticeable on 'stroker' engines that may experience higher crankcase pressures (due to rotating assembly's increased mass) possibly blowing out 'loose' dipsticks and oil mist out of poorly fitted passenger side vent/filler caps at higher RPM's.