I have a very very basic operating principles question for you regarding the FD620D crankcase ventilation system.
In post-1960’s conventional naturally aspirated auto engines with a PCV system, fresh air (usually filtered) is allowed to enter the crankcase (via valve cover breather caps or some other means). This air and crankcase vapors are then expelled via the PCV control valve plumbing back into the intake system to (hopefully) be combusted. If you consider the crankcase as a lung, there is an “inhale” flowpath and an “exhale” flowpath. Like attached:
For the FD620D, considering just the crankcase, I feel I fully understand the “exhale” operation and flowpath – (a) crankcase vapors exit via the reed valve in the “breather chamber”, (b) the metal baffling in the chamber hopefully does a basic air-oil separation job and liquid drains back into the crank via the drain hole in the chamber, (c) remaining vapor exits the breather chamber via a hose to some point upstream of the throttle body. And at idle there should be some vacuum on the crankcase as measured with some form of manometer.
But it appears to me there is no “inhale” flowpath for this engine. There’s no breather cap on one of the valve covers, the oil fill cap on the other valve cover is sealed to a degree. Where else can fresh air be introduced to the crankcase?
So – am I correct in thinking that in the FD620D, fresh air does NOT enter the crankcase? Or am I missing something……
In post-1960’s conventional naturally aspirated auto engines with a PCV system, fresh air (usually filtered) is allowed to enter the crankcase (via valve cover breather caps or some other means). This air and crankcase vapors are then expelled via the PCV control valve plumbing back into the intake system to (hopefully) be combusted. If you consider the crankcase as a lung, there is an “inhale” flowpath and an “exhale” flowpath. Like attached:
For the FD620D, considering just the crankcase, I feel I fully understand the “exhale” operation and flowpath – (a) crankcase vapors exit via the reed valve in the “breather chamber”, (b) the metal baffling in the chamber hopefully does a basic air-oil separation job and liquid drains back into the crank via the drain hole in the chamber, (c) remaining vapor exits the breather chamber via a hose to some point upstream of the throttle body. And at idle there should be some vacuum on the crankcase as measured with some form of manometer.
But it appears to me there is no “inhale” flowpath for this engine. There’s no breather cap on one of the valve covers, the oil fill cap on the other valve cover is sealed to a degree. Where else can fresh air be introduced to the crankcase?
So – am I correct in thinking that in the FD620D, fresh air does NOT enter the crankcase? Or am I missing something……