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Re: [T3] Oil forced out of breather


On 5 May 2004 at 18:54, Dave Hall wrote:

> > > If reduced crankcase pressure prevents oil being expelled from the breather,
> > > increasing the pressure to atmospheric would encourage an airflow through to
> the
> > > breather and air cleaner, which might lead to it picking up oil on its way
> > > through the narrower breather channels.  Also, the cool air would expand a
> bit
> > > too when warmed by the engine.
> >
> > Not sure what you're suggesting here, but in 72-3 there is no flow from the
> > breather to the air cleaner.
> >
> 
> That's a reference to the fault condition when the RC gasket is displaced at the
> top and isn't sealing, so is letting in air at atmospheric pressure.  This I
> presume is the way oil can be blown from the breather instead of draining back
> to the sump - too much air flow through the breather prevents normal oil
> separation from the mist to happen quickly enough..

The problem I have with this is that it assumes that we can have suction at the 
VC gasket (otherwise air wouldn't get sucked in) at the same time that we have 
pressure at the breather (where oil mist is getting blown out.) Since we're 
just talking about the pressure in two different parts of the same chamber, I 
think this would be hard to defend.  

It's clear that the pressure in there will be pulsating, but I'd still expect 
the average pressures at those 2 points to be the same. The only way I can see 
that we could get there to be a net flow of air into the rocker boxes would be 
to come up with some kind of check valve that allows air to only pass inwards 
past the VC gasket.   

-- 
*******************************
Jim Adney, jadney@vwtype3.org
Madison, Wisconsin, USA
*******************************

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