At 01:54 AM 3/12/00 -0500, Stephan wrote:
>Ok, I'm a little confused about the PCV function vs just a plain tube to the
>air cleaner or carb. What is the difference in function? Which should go
>where or would it be best to have 2 PCVs? I've removed most of the smog
>crap off the motor but want to maintain a closed system. thanks in advance
>to anyone that can clear this up.
Stephan,
This sounds like a good discussion item for the Novice Corner. Since
I don't have everything back on the engine (all the vac. hoses and such)
I'm not too sure what you are asking.
But I think you are refering to the hose that comes off the pass. side
valve cover. Now that you mention it, it is an interesting question.
I don't know that I can answer it. Maybe one of the other more learned
members can give a better explanation.
Basically the PCV - Positive Crankcase Ventalation - did away with the
open breather tube from the crank case to the atmosphere. In the past,
the fumes - oil, gas, etc - that were generated by some of the fuel
burning on the power stroke, slipped past (blow by) the rings and went
into the sump (oil pan). There was simply a hole drilled in the block
and a tube attached that would let this excess pressure vent to the
atmosphere.
As engines wore, the amount of blow by collected in the crankcase increased.
Thus causing some polution. In the mid 70s the EPA started to require
manufactures to reduce the total pollution of the car. This was on of the
first places the manufactures started. They simply sealed up the hole
in the block. This would now allow the pressure to build. Since there
are oil drain back holes in the head to allow the oil that is lubricating
the valve assemblies, and holes for the push rods, the pressure is NOT
restricted to only the pan. As the pressure increases, it will expand
from the pan into the valve cover area looking for a way to escape.
So a hole was placed in the valve covers to relieve this pressure.
However, the idea was to NOT vent this to the atmosphere. So the routed
it back to the intake of the carburator. Thus allowing these excess vapors
to be burned.
I don't know when the actual PVC valve was added, and I'm not quite sure
of its operation. Basically all it the PCV valve is, is a BB that is
allowed to float in a verticle tube. When there is no pressure, the
gases are kept in the engine. As a function of either, or both, increased
crankcase pressure and vaccumn, the BB is allowed to lift off its seat
and the gases are allowed into the carb. Same as above.
As to your questions:
"What is the difference in function? Which should go where or
would it be best to have 2 PCVs?"
I don't know. However, my mind, one tube should be more than enough to
handle the excess vapors unless you have a very worn eng. and a very high
compression ratio. But here is where I'll defer to the more learned
members of our group. Anybody?
John
John T. Blair WA4OHZ email: jblair@exis.net
Va. Beach, Va Phone: (757) 495-8229
48 TR1800 48 #4 Midget 65 Morgan 4/4 Series V
75 Bricklin SV1 77 Spitfire 71 Saab Sonett III
Morgan: www.team.net/www/morgan
Bricklin: www.bricklin.org
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