PCV Valve question

[mdmcs1]

i took the stuff out of my flame arrestor but kept the hose hooked up from it to the air cleaner. works perfect and i dont have to worry about the flame arrestor being plugged up anymore

[Jay Tabor]

on a pcv system that is plumbed correctly and working correctly
the pcv valve and hose should/will have manifold vacuum in it 15"hg [+-]
[lots o' suction] [if engine is running , and not at WOT]this sucks all the crankcase fumes/blowby from inside the engine. the resulting low pressure/vacuum inside the engine/crankcase is alleviated by the filtered fresh air source plumbed from aircleaner to usually a valve cover/or oil fill pipe.
blowby is down low in crankcase therfore the suction is applied low[ valley cover/sometimes valve cover] the fresh air comes in at top of engine to help all the blowby/fumes get directed to the suction side and thereby helps evacuate all those 'fumes'. keeping the innards clean, less sludge, less smog in the air, all sorts of good thingd.
now does the flame arrestor stop errant flames from being sucked into the fresh air source side of pcv system? [down hose from aircleaner to valve cover in case of backfire in carb?]? it might, specially in those 'ahem' rolling wrecks that have weak spark, massive blowby and gasoline leaking carbs and fuel pumps which we read about every so often!
in a good, non defective running engine it aint necessary, why would there be any gasoline fumes inside the block??
the steel wool inside the arrestor stops and breaks up a flame front from getting thru to the cylinder head, its better purpose- is it stops and holds all the oil vapor from blowing up thru hose to airfilter getting it all oily, course if you use a oil bath air filter or a Kand N or Amsoil reusable air filter which need an occasional oiling it dont matter.

[GreatScout]

Ahhh, now you see? I got the answer I needed to know. One from a live experienced driver (incorrect application of the PCV) and one from a well trained 'hands on' tech from trh ol' school!

Dennis & John, Thanks for the responses. My own light bulb just got a bit brighter

[mdmcs1]

i have put over 12,000 miles on my scout since i took the stuff out of the arrestor, have not had even the slightest residue of oil in my air cleaner yet. has worked perfect so far.
besides, if the pcv valve is working right, and air is being drawn from the air cleaner through the breather hose, the oil shouldnt be trying to get up to the air cleaner in the first place. right?

[Jay Tabor]

except for WOT application/excessive blowby
the WOT theory is- low man vac. and high cyl pressure, creates some pressure in crankcase, resulting in a little vapor going up vent hose to aircleaner.
in the old days driving long roads it was easy to spot dips/rises in the road, looking at the oil/grease track down center of lane, if one noticed the track dissappear for a ways then get much darker, that was an indication of a dip/rise in road-the vehicle approaching a dip would let off the gas pedal = high man. vac.= low blowby= no oil in road dripped out of road draft tube.
now then- as the vehicle passed thru the ditch, dip and acclerated up and out, the heavy accelration would create a lot of crankcase pressure = resulting in lots of blowby= oil streak on road surface. this is very important for motorcycle riders= a clue as to road surface, especially when going way fast!
and now you know------- the rest of the story!

[Bharris]

The PCV valve in my 1975 345 is a screw in type as well as the breather. I understand the function of each, any idea what the part numbers might be for either of them. Any useful information would be much appreciated.
Thanks,
Blain

[Ike T]

Originally Posted by Bharris

The PCV valve in my 1975 345 is a screw in type as well as the breather. I understand the function of each, any idea what the part numbers might be for either of them. Any useful information would be much appreciated.
Thanks,
Blain

For the Flame Arrestor, try 400858C1.

Tim

[Bharris]

Ok next PCV question. I did not replace my pcv because I could hardly get any air through in backward, and it rattled like all was loose inside. Question - I can get a very little amount of air through, should it be none?

[Doc Stewart]

The PCV is a valve: If you suck on the carb side, it should allow air through. If you suck on the crancase side, it should not. A good cleaning with carb solvent fixes most of them. What goes bad is the rubber grommet: smear some silicone goo around the body of the valve and push it back into the grommet. You will hate me when you pull it out next time but it will work.

[Bharris]

It is the thread in type valve. If I pull it out I can get a small amount of air through from the crankcase side. Is it an all or none proposition?