PCV and valve cover vent

[Breitenbucher]

I have a couple of questions for the experts of these stovebolt 235 engines related to Deves’ PCV conversion and vacuum. This 1957 truck engine has no oil splash guard. There is a single bolt hole for it with a screw plugging the hole but no baffle was in the engine. Far as I know the engine has never been apart before. First question, can I install the PCV mod without the baffle or do I need to find or make one to install? The other issue with this engine is someone drilled a hole in the top of the valve cover and brazed a short tube onto it where a 3/8” hose was run to a similar tube brazed on top of the air cleaner cover. There was a sealed oil fill cap on top of the valve cover. Seams like this would counter the PCV, applying vacuum to both ends. I like the idea of the valve cover sucking filtered air from inside the air filter since this engine will be operated in a dusty environment but not if it will interfere with the PCV operation.
thanks in advance for any help.

[Deve]

I can't answer the question about how the home-made PCV valve cover mod affects things. I CAN answer the question about the baffle. All 235 engines of that era came with the internal baffle. It was a good idea to keep oil from splashing into the road draft tube which was bad enough already in its ability to leak oil on your garage floor. My PCV mod takes all of this into consideration. Due to physics, it doesnt matter the location of the valve. Move the valve further up the line, same vacuum will pull oil up the line. You could put it at the intake manifold and barring leaks in the tubing or hose, the very same 'pull' will be in effect. To ensure oil doesnt get into the intake and cause the engine to have a smoking problem, I even made sure to use 3/8" tube so shear volume would make it impossible to pull up that much oil. THEN, I use a V-237 valve. This valve only pulls .95 psi out of the engine. Less than 1 psi is so small a number that the only thing that is going up that tube is crankcase gasses. Me being the perfectionist I am, I would find a baffle and put it in just because. If you don't, it wont cause oil to suck into the intake.

All that being said, if you can figure out how to mount the PCV Valve to the valve cover and figure out how to make a hole in the air cleaner to make a more modern solution, that is just fine. My system works the same in the end, but I would not mix the two. I hope others reply because I know how it sounds from me having self interest in mind. Not the case, but I understand.

[Pre68Dave]

All the baffles I have seen are held on by two screws. See picture

[Deve]

Yeah, that's my experience too Dave. Simple sheet metal screws. Hope life is treating you well!

[Pre68Dave]

Picture of baffle.
All is well here Deve!

[Breitenbucher]

Yes I did find both mount holes for the baffle, one had a slotted screw in it and the other had a strange looking plug in it that looks like a big thumbtack with an 1/8” shank stuck in there that I had to punch out from the inside. Is anyone selling these baffle plates? Back to the PCV issue. I definitely want to put the PCV in the draft tube hole since this engine is going into a forklift that has no ‘road speed’ to cause any draw. Also will work in a dusty environment so I don’t want any air coming into the engine that doesn’t have a good air filter. Deves’ PCV mode calls for an oil fill cap that is vented and, I think, has some kind of a small air filter in it. I would rather use the brazed on tube on my valve cover to hose over to the tractor style air cleaner I’m going to use, question is there going to be too much vacuum inside the air cleaner that will diminish the vacuum on the intake manifold going to the new PCV mod. I’m still sketchy on the airflow through the engine. Reading some of Deves’ articles on the earlier engines they actually had vent holes in the top of the valve cover and I think he mentions air flowing downward from valve cover, through the engine and crankcase and out the draft tube or new PCV mod. How does air from within the valve cover get to the crankcase? I understand some blow by would cause positive pressure within the crankcase that would be great to route back into the intake manifold through the PCV but is the PCV continuously pulling air from within the valve cover, through the engine and crankcase, seams like the air would have to go through the oil passages.
thanks for any advice.
Paul

[Deve]

Dave? Seems if he just put the PCV inline with the valve cover port to the air cleaner he could put a freeze plug in the road draft tube and be done with it? You could maybe explain clearer about how air circulates through the engine?

[Pre68Dave]

It is true, one would plug the road draft tube hole completely and do it all from the valve cover.
in that case a PCV valve would be installed in the rear of the valve cover, but a baffle would be needed inside the cover to prevent splash from the rockers being sucked up the PCV valve.
I think I would be easier to find the correct baffle.
maybe put an add in the parts want section on the Stovebolt forum.

[Deve]

My take on air circulation is pretty basic. Until 1962 the crankcase gasses were evacuated by using a road draft tube with the end of the tube shaped in such a way as to invoke the venturi principle. At 30 mph, the air stream sucked the gasses out. Before a 30mph wind, not much happening. This caused more crud to accumulate in the engine. After 1962 (with the exception of the 58-62 261 on some larger trucks) Chevy decided to suck the gasses out via the valve cover (to air cleaner) system. So, air DOES circulate from bottom to top OR top to bottom depending on how you look at it. If you have a 216/235/261 it's just easier to put the valve in the road draft tube hole. A person could make a baffle with rudimentary tools if nothing else. Either way, it solves the ventilation issue quite nicely.

[Breitenbucher]

Well, I’m still baffled (pardon the pun) on how air passes from within the valve cover cavity to the crank case but assuming it does then it makes sense to have an intake on one or the other to allow air in as the PCV sucks it out and into the intake manifold. The draft tube doesn’t work for me since my engine will operate fairly stationary in a forklift so I like Deve’s PCV mod. Since the engine will also be working in a dusty environment I don’t like the small filter on the oil filler plug. Since my valve cover already has a short tube brazed onto it I would like to run a hose from it to the air cleaner for the intake vent but I’m concerned it may have too much vacuum and defeat the draft tube PCV mod. Any suggestions is very much appreciated.
thanks,
Paul

[Deve]

I can't imagine that working very smoothly since you are using the carb throat and the intake manifold but only one is metered (the valve). Those Stant 10064 oil filler filter caps are cheap (around $5) and the filtering is decent. That said, maybe you could modify an actual air filter. If it were me, I would use a lawn mower one like what I use on my 261 for the original air cleaner. http://devestechnet.com/Images/Proje...yfilter1lg.jpg
A person could get whatever air cleaner and just adapt it to the oil filler hole. I can see that using the PCV style cap, cutting off the top and it could be very close to the proper diameter. On something that is sitting stationary, it would make sense.

[Breitenbucher]

Ok, got it. That gives me the idea to just run my valve cover ‘brazed on tube’ over to a second (separate) air filter.
Thanks Deve.