Dave
If this has been happening since the first day the engine was de-smogged,
then the setup is wrong.
If it just started happening, something changed.
The PCV system is designed to apply a slight vacuum to the crankcase and
serves two functions:
1. To remove exhaust gasses that slip past the rings and valve stems into
the crankcase and
2. To prevent major oil leaks in the engine by preventing pressure from
building up inside the crankcase.
A PCV valve is mostly a check valve, to prevent backfire flames from
igniting gasses inside the crankcase.
A hose from the timing cover through the PCV valve and connected to the
intake manifold pulls FAR too much volume of air, and winds up pulling oil
out of the crankcase. Having a vented cap INCREASES the ease at which that
volume of air can be pulled.
The system I have been able to get to work is this:
Sealed cap
No vent in the valve cover at all. (This makes it so the only air that can
be pulled out of the crankcase is pulled IN through the scroll seal at the
back of the engine, and any blow by that makes its way past the rings).
Hose from can on front of timing cover
Insert a plug into the hose at the top end, and drill a 1/8" hole in the
plug. This gives you an orofice to restrict the volume of air that is
pulled out of the crankcase.
Hose connects to the british diaphram style PCV valve, mounted to the intake
manifold.
If the car still belches oil out the rear main seal or dip stick tube under
heavy load, increase the hole size in your orofice to 3/16 and try again.
If the car still belches oil out the rear main seal or dip stick tube under
heavy load, increase the hole size in your orofice to 1/4" and try again.
If the car still belches oil out the rear main seal or dip stick tube, you
probably have bad rings or a broken ring causing excessive blow-by and
excessive crankcase pressure.
If you are running 20/50 engine oil and you experience oil fogging that
begins about 2 minutes after you start driving but clears up after the
engine has risen to opperating tempurature, try running 10/40, or even 5/30
oil. I had an issue where the thick oil wouldn't drain out of the head fast
enough, and would then be pulled in via the valve guides and burned. The
thinner oil drains from the head faster and won't fill up the valve cover
like the thicker oil can.
David Riker
----- Original Message -----
From: "David Ambrose" <stargazer1@cox.net>
To: <Spridgets@autox.team.net>
Sent: Monday, January 17, 2011 12:00 PM
Subject: [Spridgets] Sucking oil through PCV valve
> We have a desmogged '70 Midget. It has the earlier carbs without the
> vacuum intakes for crankcase ventilation and has been fitted with a PCV
> valve. It's taken to pulling oil into the carbs via the PCV valve. The
> valve itself seems OK, but I can't think of any other reason for the
> problem. We've already been through the sealed vs. vented oil filler cap,
> and have a vented cap on the car.
>
> Any ideas appreciated. I don't particularly want to order another PCV
> valve for no good reason.
>
> Thanks,
> Dave Ambrose
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