Re: [AMC-list] oil coming out of dipstick

["Chris Peters" <cpeters1@xxxxxxxxxx>]

Marty,

Based on your comment below about running a hose from the oil filler cap to
a T-fitting I think you misunderstand how a PCV system works.  The purpose
is to remove gaseous fumes from the crankcase caused by blowby past the
rings.  These fumes are potentially explosive since they are basically
unburnt air fuel mixture.  The hose between the carb and the PCV valve is
used to suck these fumes from the crankcase due to the normal engine vacuum
under the carb.  You will note the carb fitting is below the throttle
butterflies, causing vacuum on that port at all time, other than WOT maybe.


Now, the second part of the system is the oil cap on the oil filler tube
(AMC's) which should have a hose on it leading to the aircleaner.  This
provides fresh air into the crankcase.  Fumes are removed via the PCV and
air replaced via the oil cap breather.  Routing the oil cap breather to the
PCV hose would do nothing good, and in fact would likely defeat the system
all together as it would not allow any fresh air to enter the crankcase to
replace the fumes being sucked out, and thus no fumes being sucked out.

Also, I finally just happen to learn today the real purpose the PCV valve.
Imagine you had no PCV valve, and you had a backfire.  It would be possible
then for that backfire to travel through the hose from the carb base to the
crankcase and ignite the fumes in the crankcase.  The PCV valve prevents
this backflow due to backfire.  

So assuming you have a good PCV valve, engine is running at idle with good
vacuum, you should have a slight vacuum on the oil filler tube, assuming you
have an otherwise sealed up crankcase (ie no breathers in the valve covers).
I suppose on a fresh engine, you might still have more blowby (rings not
sealed yet) or at WOT you would have more blowby than the PCV system can
handle (since at WOT you have little vacuum) and that blowby would cause
crankcase pressure which would have to exit the crankcase some place, likely
your oil cap, or valve cover breathers, or in your case, oil dipstick tube.

Chris Peters
70 Javelin SST
www.thepetersgarage.com

-----Original Message-----


Message: 4
Date: Tue, 9 Jun 2009 19:08:55 -0700 (PDT)
From: Marty Bricker <mbrickerusn@xxxxxxxxx>
Subject: [AMC-list] oil coming out of dipstick
To: amc-list@xxxxxxxxxxxx
Message-ID: <314749.71029.qm@xxxxxxxxxxxxxxxxxxxxxxxxxxx>
Content-Type: text/plain; charset=us-ascii


I have a problem with oil coming out of my dipstick. 

<snip>

I thought of reinstalling the original fill cap (or a breather with a nipple
on it) and running a hose back to a T fitting on the line from the carb to
the PCV valve.
Any other suggestions?  Thanks.  
Marty   



      


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