Basics:
- an engine crankcase will always be somewhat pressurized due to blow-by (all
engines have some blow-by)
- earlier engines--like our BN2 and my dad's '46 Chevy two-ton--have a tube
from the crankcase open towards the ground
to vent the pressure (aka a 'road draft' system)
- a PCV system uses manifold vacuum--not pressure--to basically suck pressure
and fumes from the crankcase into the
intake manifold so that it can be (re-)burned in the engine
- since a PCV valve is basically a vacuum leak, the valve has to mostly seal at
idle so as not to produce a lean-running
condition (plus, it has to seal in the event of a manifold backfire so as not
to ignite the fumes in the crankcase)
A true PCV system will have a source for clean fresh air so the gases can
circulate, usually a tube from inside the air
cleaner and sometimes from a separate air cleaner. The debate here centers on
whether or not a fresh air source is
required. It's definitely a good idea, but there's enough sources of air--like
leaks at the rear scroll seal or valve
covers--to provide an air source (albeit unfiltered).
I'm sure you've tried to seal your leaks, with the usual lack of success. A
PCV valve will more than likely help
(although you'll want to determine if you have excessive pressure and what's
causing it). I once tried an aftermarket
air cleaner that didn't have a decent adapter to vent the rocker and crankcase;
I ruined a valve cover trying to seal up
the leaks.
Bob
On 2/4/2012 9:50 AM, Price Lindsay wrote:
> Sorry to jump in here but I'm somewhat of a novice and am a little confused.
> There is talk of pressure going one way or the other after installing a PCV
> valve. I've been fighting a slight leak at the real of my valve cover for a
> while now along with the usual drips here and there. Here's my question:
>
> If I put a PCV valve in as suggested, ie from the "tee" on the valve cover to
> the plug in the manifold, would the pressure exacerbate the leak(s) or
> eliminate/reduce it/them?
>
> Thanks for you help.
>
> Price Lindsay
> 67 BJ8
>
>
>
>
--
*******************************************************************
Bob Spidell San Jose, CA bspidell@comcast.net
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