Most automotive engines have pistons going up while others go down. The net
volume of the crankcase does not change, and compression does not occur into
the crankcase. Most enclosed crankcase systems (PCV) allow air in from
somewhere (usually a tube to the air-cleaner) and draw air out via the PCV
valve.
That is not true for some (very few) engines, usually these are motorcycle
engine, and the crankcase ventilation system is therefore different on these
engines.
----- Original Message -----
From: "Kent Christensen" <lkchris@uswest.net>
To: "'Buick-Rover-V8 mailing list'" <buick-rover-v8@autox.team.net>
Sent: Tuesday, October 30, 2001 10:21 PM
Subject: re: PCV Thread
> re; Enclosed crankcases have always needed ventillation due to
> vaporized oil, combustion gasses leaking past piston rings (blowby),
> etc. It all has to go somewhere.
>
> Actually they need ventilation because of the air pushed by downward
> moving pistons--wouldn't want compression in this direction and in
> this area. No need to create vacuum to draw out fumes--they'll be
> pushed out, won't they? In fact, it would seem the system would need
> to be able to breathe both directions, i.e., in and out. Perhaps
> there is always a piston going up for each piston going down in our
> favorite V8, but not on every engine, for example my BMW boxer twin
> motorcycle. I always thought the prettiest looking crankcase
> ventilation was on Indy Offenhausers.
>
> Kent Christensen
> Albuquerque
> '89 Range Rover
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