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Dual PCVs On Chev 350?



 
 
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  #1  
Old June 1st 05, 02:53 PM
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Default Dual PCVs On Chev 350?

I have a pair of nice cast aluminum valve covers for the '74 Chev
truck 350 in my street rod. Both have identical PCV holes so the valve
can be placed on either side depending on application. On mine, the
driver side has a rubber grommet for the valve and the passenger side
has a rubber plug. Both parts are too deteriorated to use. Problem
is, my local Chevy dealer can order the grommet but they have no
listing for the plug. I've looked for an after-market plug but I
haven't found one that fits. I really want to use the covers so I'm
thinking of putting a grommet and valve in each side and connecting
them to the intake with a "T" fitting. Is there any reason I
should NOT do this?

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  #2  
Old June 1st 05, 03:26 PM
Anumber1
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Default


> wrote in message
oups.com...
>I have a pair of nice cast aluminum valve covers for the '74 Chev
> truck 350 in my street rod. Both have identical PCV holes so the valve
> can be placed on either side depending on application. On mine, the
> driver side has a rubber grommet for the valve and the passenger side
> has a rubber plug. Both parts are too deteriorated to use. Problem
> is, my local Chevy dealer can order the grommet but they have no
> listing for the plug. I've looked for an after-market plug but I
> haven't found one that fits. I really want to use the covers so I'm
> thinking of putting a grommet and valve in each side and connecting
> them to the intake with a "T" fitting. Is there any reason I
> should NOT do this?
>

Yes,
A PCV system has to draw fresh air into the crankcase somehow.
The traditional arraignment is to use a PCV valve on one side and a Breather
/ intake filter on the other to provide the clean air supply. Two vacuum
sources leave no way to introduce the fresh air.

--
Alan Gallacher
Born to Tinker!


  #5  
Old June 2nd 05, 02:40 PM
Hairy
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Default


> wrote in message
oups.com...
> I have a pair of nice cast aluminum valve covers for the '74 Chev
> truck 350 in my street rod. Both have identical PCV holes so the valve
> can be placed on either side depending on application. On mine, the
> driver side has a rubber grommet for the valve and the passenger side
> has a rubber plug. Both parts are too deteriorated to use. Problem
> is, my local Chevy dealer can order the grommet but they have no
> listing for the plug. I've looked for an after-market plug but I
> haven't found one that fits. I really want to use the covers so I'm
> thinking of putting a grommet and valve in each side and connecting
> them to the intake with a "T" fitting. Is there any reason I
> should NOT do this?
>


Anumber1 has it right. The original air cleaner had a hose going from the
valve cover to the air cleaner providing filtered air to the crankcase. If
you are using an aftermarket air cleaner with no provision for crankcase
ventilation, go to Summit or similar and get a grommet and filter that will
plug into it. Do not just plug the hole.
H


  #6  
Old June 2nd 05, 02:46 PM
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Default

What you folks say makes sense but here's the part I don't understand
(sorry - didn't give complete info in my first post):

Aside from the PCV holes, the only other hole is the oil fill in the
passenger side. The cap, which sure looks like OEM, is the screw-in,
NON-breather type - in fact, it has the rubber gasket to seal it to the
cover. The covers and cap were on the car when I got it - took them
off to clean them up and found the rubber parts are toast. Anyway, it
seems to run OK.

Although...it sometimes dies on cold start and it idles a little high -
maybe to compensate for lean mixture? And, I've had trouble with oil
leaks - maybe vacuum breaking the gasket seal?

I was looking for a plug in the auto parts stores but I just remembered
the local hardware store has some polyethelene button plugs that might
work. Sounds like I also may be looking for a breather cap for the oil
fill.


wrote:
> I have a pair of nice cast aluminum valve covers for the '74 Chev
> truck 350 in my street rod. Both have identical PCV holes so the valve
> can be placed on either side depending on application. On mine, the
> driver side has a rubber grommet for the valve and the passenger side
> has a rubber plug. Both parts are too deteriorated to use. Problem
> is, my local Chevy dealer can order the grommet but they have no
> listing for the plug. I've looked for an after-market plug but I
> haven't found one that fits. I really want to use the covers so I'm
> thinking of putting a grommet and valve in each side and connecting
> them to the intake with a "T" fitting. Is there any reason I
> should NOT do this?


  #7  
Old June 2nd 05, 04:00 PM
Mike Romain
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Default

You don't have the correct air filter on it right?

Therefore you have no PCV intake into the engine. This can cause oil
leaks. Sometimes the system builds up more pressure than the PCV can
suck off and normally this pressure is just vented back into the air
filter. Now, it vents out an oil seal...

The PCV system needs to be balanced with an air intake matching or
better said tuned to the PCV suction.

Very likely you can get a filler cap with the vent in it for a 350.

If you have a bad air filter, you also will have issues with the carb
freezing up because you also no longer have the heat pipe to the
intake. This can happen in high humidity at above freezing or even turn
it into one solid block of ice on the highway. It's 'not' fun realizing
the gas pedal is stuck at 55 mph in a snowstorm.....

You also can't pass emissions in most places with a defective PCV and no
hot air intake to the carb.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's

wrote:
>
> What you folks say makes sense but here's the part I don't understand
> (sorry - didn't give complete info in my first post):
>
> Aside from the PCV holes, the only other hole is the oil fill in the
> passenger side. The cap, which sure looks like OEM, is the screw-in,
> NON-breather type - in fact, it has the rubber gasket to seal it to the
> cover. The covers and cap were on the car when I got it - took them
> off to clean them up and found the rubber parts are toast. Anyway, it
> seems to run OK.
>
> Although...it sometimes dies on cold start and it idles a little high -
> maybe to compensate for lean mixture? And, I've had trouble with oil
> leaks - maybe vacuum breaking the gasket seal?
>
> I was looking for a plug in the auto parts stores but I just remembered
> the local hardware store has some polyethelene button plugs that might
> work. Sounds like I also may be looking for a breather cap for the oil
> fill.
>
>
wrote:
> > I have a pair of nice cast aluminum valve covers for the '74 Chev
> > truck 350 in my street rod. Both have identical PCV holes so the valve
> > can be placed on either side depending on application. On mine, the
> > driver side has a rubber grommet for the valve and the passenger side
> > has a rubber plug. Both parts are too deteriorated to use. Problem
> > is, my local Chevy dealer can order the grommet but they have no
> > listing for the plug. I've looked for an after-market plug but I
> > haven't found one that fits. I really want to use the covers so I'm
> > thinking of putting a grommet and valve in each side and connecting
> > them to the intake with a "T" fitting. Is there any reason I
> > should NOT do this?

  #9  
Old June 2nd 05, 05:52 PM
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Default

OK, the pieces are falling into place thanks to you folks' help. Again
I apologize for giving less than complete info - should've realized all
this stuff is interrelated. If I've got the numbers decoded correctly,
the engine is a '74 Chev truck 350. It's in a '38 Plymouth coupe that
probably weighs under 3K lbs. Supposedly the engine has about 50K
miles. It doesn't burn oil, maintains a consistent 190 temp and, aside
from the aforementioned starting/idle problems (which don't seem that
serious), runs good. It's stock except for Mallory ignition,
Edelbrock manifold, Holley 570 cfm 4-bbl, and dual exhaust on OEM
ram-horn manifolds. It's hooked to a 350 auto with shift kit and a
Nova rear - haven't checked the ratio but I expect it's in the 3.00 -
3.50 range. The air cleaner is after-market - basically a 9-inch round
filter sandwiched between top and bottom plates. Carb freezing
shouldn't be problem as I don't drive the car in cold weather and
certainly not in snowstorms. For better or worse, we don't have
emissions testing around here.

Apparently the PCV grommet and the oil cap are OEM. From the
construction and fit of the plug, I assumed it is as well. But it
doesn't have a part number like the PCV grommet and the Chevy parts guy
couldn't find a listing for it. So now I'm thinking somebody blocked
the breather hole with an after-market plug when the OEM
manifold/carb/air cleaner were replaced. At this point the simplest
solution appears to be replacing the PCV grommet and oil cap with OEM
and replacing the plug with an after-market grommet and push-in
breather - all those parts should be available.

Thanks again for everyone's help in working this out.

 




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