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Re: PCV - to vent or not to vent!

To: "Chris Kotting" <ckotting@iwaynet.net>, "Larry & Sandi Miller" <millerls@ado13.com>
Subject: Re: PCV - to vent or not to vent!
Date: Mon, 24 Jan 2000 09:47:58 -0500charset="iso-8859-1"
Cc: <spridgets@autox.team.net>
hmmm.... I think a bit of clarification is in order here.

     Yes...as Chris reiterated, the whole point is to keep a slight
vacuum on the crankcase (lower end) . This helps to keep the oil
inside the crank and not leaking out through the rear crank journal
AS WELL AS to recirrculate blow-by gases to be burned in the intake.

     Depending on model year, some breather systems use a carbon
canister that also vents the gas tank and the valve cover 
(via a restrictive orifice). 
    
      The timing chain cover breather (lower end) either went through
a PCV valve directly into the top of the intake manifold, or was
routed via a Y pipe directly into the side of the carbs.

      This carb side port is 'ported vacuum' that is to say it's on the 
'atmospheric' side of the throttle plate. The high vacuum is only 
applied if and when the throttle is opened. Even then, the port 
(usually plumbed with something like a 1/4"  diameter hose) 
still only breathes through a small diameter restrictor hole into 
the carb  throat.

      Early models without the carbon canister, or vent pipe on the 
rocker cover, used the PCV valve to the manifold  with 'vented' cap.
Remember, you're pulling only a slight vacuum, you don't want full
manifold vacuum in the crank. The idea was to also pull
piston ring blow-by gases back into the intake to reduce acidic
build up in the oiling systems.

Later models using the Y pipe to the carbs, the carbon canister,
and having the breather pipe on the rocker cover used a non-vented cap.

Paul Tegler  wizardz@toad.net        http://www.teglerizer.com 
OBie - '73 BGT - daily driver  
http://www.teglerizer.com/mgstuff/ob_description.htm
Punkin' - '78 Spitfire - corner ripping screamer 
http://www.teglerizer.com/triumphstuff/spit78.htm
Lil' Greenee - '73 RWA Midget - lady killer  
http://www.teglerizer.com/midgetstuff/index.html





Paul Tegler  wizardz@toad.net        http://www.teglerizer.com 
OBie - '73 BGT - daily driver  
http://www.teglerizer.com/mgstuff/ob_description.htm
Punkin' - '78 Spitfire - corner ripping screamer 
http://www.teglerizer.com/triumphstuff/spit78.htm
Lil' Greenee - '73 RWA Midget - lady killer  
http://www.teglerizer.com/midgetstuff/index.html

-----Original Message-----
From Chris Kotting <ckotting at iwaynet.net>
To: Larry & Sandi Miller <millerls@ado13.com>
Cc: spridgets@autox.team.net <spridgets@autox.team.net>
Date: Monday, January 24, 2000 8:09 AM
Subject: Re: PCV


NON-vented.  Regardless of how you plumb it, a vented cap will render
the PCV ineffective.  (The function of a PCV system is to keep the
crankcase at slightly less than atmospheric pressure, a vented cap keeps
the crankcase at atmospheric pressure.)

Chris Kotting
ckotting@iwaynet.net

Larry & Sandi Miller wrote:
> 
> I'm installing a PCV on the 1275 this week.
> 
> Should I use a vented or non-vented cap?
> 
> Larry Miller


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