HI Group, I have seen many PVC valve arrangements. On the 235 inline 6. On the valve cover to air filter or old vacuum line where wipers went and crank case to filter and or old vacuum line where wipers went. Which one is the best for the engine. Sucking from crank case or top of valve cover and where is the best place to have it go, air filter or old vac line of wipers? Hope to get the best one for the engine
Poly Vinyl Chloride? (Just messing with you brother. ) I have seen many PCV arrangements on these trucks as well. Some of them are a bad idea in my opinion. If I were to rig mine with a PCV, I would rig it as similar as possible to a more modern inline six. I believe that it is important to have the vacuum applied to the top of the valve cover to remove the water vapor which is known to rise to that location. The vented valve covers on the '54 and earlier engines serve a dual purpose. 1) While underway on the open road, fumes are sucked out via the downdraft tube. This air is replaced through the vents in the valve cover. 2) While at low speeds or idle, fumes (water vapor mostly) rise to the top of the engine and are allowed to escape via the vents. Folks have written about filling the vent holes and adding a vented cap which has filter material in it. When they removed the valve cover after driving for a significant amount of time, they discovered creamy goop on the underside of the valve cover. This would be indicative of the accumulation of water vapor which had no way to get out. Carl
1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission
Ok I have a 1956 235 with a downdraft tube and a screw in breather cap that is in the center of the valve cover. So if I had a breather cap with a 3/8 spigot on it , Should I run it to the wiper motor vac port. I will also be running power brakes. Can I also run that to the same vac port.. This vac port is the same one the wipers used to run off of. Please let me know if this will work as I mentioned, thanks
Why not go with the factory arrangement? (RPO 217) See sect 0, sheet 4 of the factory assembly manual. It works for me.
What year/years is that Manual?
There is a Manual that covers 1953 trucks and a Manual that covers 1956 (trucks)? There are several Manuals that cover car years during which a 235 was available.
Are the PVC systems the same for those two "generations" and various years of 235s?
trihawker - which generation (car or truck) 235 do you want to "match". Most likely the 47-55st Chevrolet Truck Assembly Manual.
Although, I am sure that I have seen (and, people have written about) different PVC "factory-plumbing" on engines from those years. Recent posts have discussed placing the PCV in several locations on a variety of 216/235/261 engines.
Sorry, trihawker, about confusing the answers to your "straight forward" question. "On the valve cover to air filter or old vacuum line where wipers went and crank case to filter and or old vacuum line where wipers went. Which one is the best for the engine."
Watching this post , I just installed a 1959 261 in my truck which came with what I believe a factory pcv. mounted on the top of the crankcase ventilator tube . I pointed the pcv down and run the hose under the motor and up the other side to the intake manifold . I have another valve cover with a fitting on the carb. side towards the front and another fitting towards the back on the dist side but chose to run it under the engine just to keep the top free of clutter . That was the idea I had , just not sure if it was a good one ???
I have been wondering why couldn't you use the same setup they used starting in the late 60's ? Just a PCV on one end of the valve cover, and a breather on the other end. That seems so simple.
Last edited by 4100 Fire Truck; 03/05/202011:10 PM.
Poly Vinyl Chloride? (Just messing with you brother. ) I have seen many PCV arrangements on these trucks as well. Some of them are a bad idea in my opinion. If I were to rig mine with a PCV, I would rig it as similar as possible to a more modern inline six. I believe that it is important to have the vacuum applied to the top of the valve cover to remove the water vapor which is known to rise to that location. The vented valve covers on the '54 and earlier engines serve a dual purpose. 1) While underway on the open road, fumes are sucked out via the downdraft tube. This air is replaced through the vents in the valve cover. 2) While at low speeds or idle, fumes (water vapor mostly) rise to the top of the engine and are allowed to escape via the vents. Folks have written about filling the vent holes and adding a vented cap which has filter material in it. When they removed the valve cover after driving for a significant amount of time, they discovered creamy goop on the underside of the valve cover. This would be indicative of the accumulation of water vapor which had no way to get out. Carl
I'm somewhere in the middle of adding a PCV valve to my 1955 235. The more I read on the subject the more questions I have. If you adapt the road draft tube to accept a PCV valve and plumb it over to the intake manifold, does the additional air from the crankcase cause a lean mixture condition? In my case, I have an unvented valve cover with a filtered oil fill cap. Perhaps it's such a small amount of air that it doesn't have a noticeable affect on the engine's efficiency.
To remove moisture from the valve cover area, an open hose from the valve cover to the air cleaner coupled with the addition of a PCV valve should accomplish that, right? That probably works well with an oil bath air cleaner, but what about a paper element air filter?
Does it matter where the PCV valve is located, crankcase or valve cover? It seems that we addressing two main issues: crankcase gases and moisture. Of course, both are harmful to the service life of our stovebolts.
I'm sure there are reasonable answers to my questions and hopefully all of you can straighten me out on this. Otherwise, the time-tested road draft tube may just continue to reside on the 235............ I don't notice much coming out of the draft tube, but after the truck has been driven and parked for a while, there's an oily sheen on the garage floor, not a puddle just a sheen.
Last edited by HandyAndy; 03/05/202011:39 PM. Reason: Engine Positive Ventilation Instruction image added.
The GM engineers who developed the PCV system for commercial vehicles had some very good reasons to design I the way they did. It works. Any attempt to outsmart the guys who got paid handsomely to develop that system by "smarter" hottrodders and hobbyists probably isn't going be very successful. It's easy to duplicate the factory setup, and the way the line from the road draft tube is routed isn't very important- - - -over the valve cover, in front of or behind it, and even under the oil pan shouldn't make much of a difference. The under the pan approach doesn't make sense to me, but that's just my opinion. Opinions are like "noses"- - - -everybody's got one, and some of them are pretty "smelly"! Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
That is the air INLET port. The PCV valve on that system pulls the air from the hole in the block where the road draft tube would normally go, from a standpipe that goes up to about the level of the cylinder head to avoid pulling liquid oil into the PCV valve. If you're going to suck air and crankcase vapors OUT of the engine, you've got to put air IN there first. Those systems used a sealed oil fill cap and drew air from the "clean" side of the air filter.
Why does a home HVAC system have a "return air" duct? Would it work if there was no way to get air into the system so it could be heated/cooled? The PCV system works the same way. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
Is there a line from the valve cover into the air cleaner in/on the 1960 261 in the photo attached below? If that is not a PCV set-up, what do you think might be the purpose of that line?
"Attached below"? Where? Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
On some USA truck 261s I have seen illustrations of the PCV tube/line being routed from the valve cover into the carburetor air cleaner.
That is the fresh air inlet to the crankcase making it a closed system. If it didn't have that it would need a breather type oil fill cap, making it an open PCV system.
BC 1960 Chevy C10 driver 261 T5 4.10 dana 44 power loc 1949 GMC 250 project in waiting 1960 C60 pasture art Retired GM dealer tech. 1980 - 2022
Ditto- - - -that line provides the air that the PCV sucks out of the crankcase- - - -PLUS all that nasty water vapor that makes the milky sludge in the valve cover. Look at the line ahead of the carburetor in that same picture that crosses the valve cover and attaches to the intake manifold. The PCV valve is on the other end of that line, attached to the standpipe from the road draft tube hole in the block.
PCV:
POSITIVE CRANKCASE VENTILATION
Air goes in, air and blow-by, plus any other vapors in the system come out. Why is this process so difficult to understand? Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
I also edited- - - -the PCV is on the other side of the engine. Can someone please post a picture of the passenger's side of the PCV equipped engine? I don't know where to go looking for one. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
Do you see a metal line "ahead of the carburetor" in the photo you posted that crosses the valve cover? That is the line that draws air through the PCV valve (which is threaded into the standpipe) and pulls it into the intake so the crankcase vapors can be burned. All PCV systems work the same way. There MUST be a flow of air through the engine. The rubber line sources that air from the "clean" side of the air filter. That line puts air INTO the engine- - - - -vapors DO NOT come out of it. Somewhere, from one of the shop manuals that people like to post pictures of, there is a complete diagram of the OEM ventilation system that shows the entire airflow of the PCV system. I simply do not know where to find that illustration.
We're like a bunch of blind men describing an elephant by touching it. One grabs the tail and says "Its like a rope" Another grabs the trunk and says "It's like a snake" Another touches the side and says "It's like a wall"- - - - -etc. Nobody sees the whole picture!
Dad's picture shows the PCV valve- - - -it's between the elbow going into the standpipe and the metal line crossing the valve cover. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
Thanks for your patience/persistence, DADS 50 & Jerry
This blind man now sees the light (the tubing routes).
I now see that the metal line that goes low behind the carburetor base is connected to that black hose (that goes to a fitting near the top of a sealed tube (instead of a road draft tube)
All of this now makes sense to this thick old head.
DADS50 - I have taken the liberty of attaching and renaming your linked-to photos (in case those links ever go bad/dead).
One image (the right-most image) has been named as a vacuum line into a vacuum distributor (on a large truck). I had a multi-vacuum-line distributor on my 54/55 GMC COE. The distributor fed the following: - vacuum-assist brakes - vacuum wipers - vacuum for GMC-only complex "switch" for 2-speed rear-end hi/lo selector
)