I've read and read all the old posts and mostly everyone has there own way of running the pcv. These are the parts I have 78 sbc 350 block Offenhauser intake with 65-67 oil fill tube (sealed cap) with threaded bung for PCV Finned valve covers with moon breathers Here's the question, after I put the pcv in the fill tube and run my hose back to the vacuum port on the carb, do I close off both Moon breathers or leave one open ?
i've never heard of closing off any of the breathers. i'm running a pcv valve in one valve cover, an open breather in the other valve cover, and my motor has the old road draft tube. works great.
I was thinking that but was also wondering if the fresh air was coming in through the carb. So both breathers open or just one ? Now if I put a vented cap on the oil fill tube the pcv wouldn't really work right ?
What's the deference in open or closed PCV ? http://www.partsamerica.com/ProductList.aspx?PartType=5&PTSet=A
Closed uses air pulled into the engine from inside the air cleaner ie filtered air. Open pulls air into the engine through a breather cap on the valve cover or filler tube ,kinda filtered depending on the cap.
leave both open the pcv is only pulling air depending on vacuum min at idle max at normal speed and none at wide open throttle. so it is only going to pull the amount of air the pcv allows one or both breathers wont effect it just make shore you have some form of filter in the breathes cuz a pcv pulls alot of air through the crank case and it will get dirt in there easy. since the whole point of it is to run the water vapor and gas vapors in your crankcase through the engine to keep the oil from getting diluted and so the fumes aret directly vented. since people care about the environment these days sorry i wrote so much don't even know if it will help but its all my experience with them. in my opinion after this road tubes are much better.
So with my moon covers and closed fill tube cap I need to buy the open pcv type ? I want to get this bought today to put the whole pcv and smoking vapor out the moon breathers behind me..lol
It will work, the Moon breathers should have a mesh filter of sorts, and by now has a bit of oil on them so that they'll do a fairly respectable job of catching the dirt, like oiling a K&N filter. I'd leave them both open. Something to remember, cars these days operate in a much cleaner invironment than in the old days.
I don't know what PCV you're getting, but make sure you install it in the right spot. I also have the fill tube with the port on it (sealed cap). I installed it on the fill tube, ran the hose to the base of the carb, and it was installed backwards and made a mess. Got a threaded hose nipple, put it in the fill tube and threaded the PCV into the carb base with a 45-degree fitting, and everything worked perfect. With you system, air will be drawn through the base of the carb, up to the top of the oil fill tube, down the oil fill tube into the lifter valley. It's still pulling, and will then pull air from under your valve covers--which will pull air in through your moon breathers. -Brad
Your system is an open system. Your breathers need some kind of filtration for the incoming air. I'd use both breathers as air intakes. Not all hot rod style breathers had filters. Some of the older ones had a series of baffles that kept the oil in. They were made to relieve racing pressure and not meant to be a filtered intake for a PCV system. Under extreme loads a PCV valve may not be able to evacuate all of the blow by. In that situation the fumes will back up and come out of the breathers into the atmosphere. They later changed to a "closed" system putting the filter element inside the air filter housing. With this set up, any back up into the air filter housing would be sucked back down the carb and not released to the atmosphere. It's just a way to keep the overflow under heavy loads out of the atmosphere. For hot rods one system is not better than the other. Both the open and closed systems work well on a hot rod. If you build 100,000 units a year the closed system will reduce emissions for a half dozen hot rods it's no big deal. Both styles do what we want done and that is to remove blow by, moisture and acids from our engines. I used Skotch-brite cut into strips and stacked inside these Offy breathers as a filter element for the incoming air. Mine is a little different than yours in the direction that the air flows inside the engine but the idea is still the same.
There have been other post about sucking oil into the PCV. Some have tried steel wool and other ways to try and stop the oil flow. I found baffeled grommets for the PCV at Speedway Motors. It says that these will stop the oil from getting into the PCV.
My filler cap is sealed, but there is a hose connection on the filler cap tower. I run a hose from there to my breather, where I modified it to accept a "stock" foam filter. It's nice because it's hidden and you can only see the black hose. The other side looks like a breather cap, but it's an integrated PCV and the line runs to the base of my carb. It works great. After a couple thousand miles, I only have a couple of little dots of oil on the foam element, so everything seems to be doing its job. In my case, valve cover baffles were critical, too. I was slinging a lot of oil on the last set of valve covers I had that didn't have good baffles in them. For yours, I think keeping both breathers on is fine. It's all about crossflow for a good PCV system to draw out the vapors....clean air in and vapors out.
Well after an afternoon of parts store chasing no one had a screw in pcv that ran the direction I needed. I bought the one NAPA (2-9255) carries that screws in to the carb spacer or intake below carb. I had to screw in an elbow in the oil fill tube and run a line from one to the other. It's not as clean as I wanted but with the front carb so close to the oil fill tube there was no way around the 90 degree elbow. While checking my cap to see if it was sealing properly I couldn't get it to seal, kept feeling air. I made a gasket out of an old inertube from a bike but still felt the air. It turns out the new oil fill tube where the neck was attached to the tube was not sealed, just some kind of compressed spot joints keeping the two halves together. I took some silicone and smeared it into the groove and all is good. I didn't test it out yet, it's to cold for the little guy and mama is at work.
So an update, it runs like shit now ! The pcv is acting like a big vacumm leak or something, stalls while sitting at the light in gear and then if you don't feather the throttle on take off it'll die too. The nipple on the pcv took 1/2 inch line, think if I tried reducing the inside of the hose with something might work ?
TTT for the morning crew, I have the pcv hooked into the carb spacer. Would restricting the air flow work and what could I use to do it ? Should I just try and put something inside the rubber line like a washer or maybe an adapter for either end to act as a restricter.
Yep,experiment with different size orifices,(is that a word?), inline. You can experiment with a piece of wooden dowel That has the same O.D. as the I.D. of the PCV hose. Center drill that with the different sizes you wish to try. For a permanent install,you can find a rubber grommet of the appropriate size and RTV it in place inside a CLEAN pcv hose. You'll get it. Stay at it.
Did you readjust your carb idle mixture? You are adding a controlled vacuum leak that introduces air into the intake that was not present when you made the original carb adjustments. You should have to back out the idle mixture screws a skosh and possibly adjust the idle adjustment screw to bring the mixture back to the desired air/fuel ratio. Mine needed the carb adjustment and all was fine after that. Actually PCV valves are made internally to pass less air at high vacuum levels (idling) than at lower vacuum levels (under a load). You can't tell that from looking at them.
I took it for a short ride yesterday before going to a cruise night and noticed the problems then. I did readjust the mixture screws and the idle is about a grand to keep it running, at the light it will drag itself down to the point of stalling if I don't throw it into neutral. I did notice I wasn't getting much out of the left mixture screw on the rear carb, never done that before either. I was about ready to scrap the whole thing by the time I made it back home lastnight.
after rereading this, it would only draw air by sucking on the threaded end and not by the nipple end. It would flow each way without a lot of preasure applied though, if I flipped it around what would be the signs of it not working ?
They are designed to flow one way. Installing it backwards will result in no flow. They are designed to close tightly if the flow is reversed which can only happen during a backfire. During a backfire they stop the burning gases from going down into the crankcase and causing an explosion. If you blow the wrong way on a PCV valve it will close off completely.
When I looked inside the pcv before installing it the nipple end of the guts inside the pcv had a flatter bigger disc looking thing than the threaded end which was smaller and looked to be stepped down. It's got to be hooked up in the right flow, just maybe that line is to big, but it makes sense that it would be closed off under idle vacuum which is greater than driving, man I'm confusing myself now...lol
The only way I can tell is to actually suck on it and blow into it. If sucking draws air and blowing shuts off the flow, then your mouth is on the manifold end. The other end needs to be connected to the crankcase some how. Where it is threaded don't mean a thing. Some screw into the oil filler tube on mid-60s Corvettes. Threads are toward the crankcase. I just got one that screws into the vacuum port on the base of a Rochester 2bbl...threads are toward the vacuum source. Both are threaded with hose nipples but have opposite flow directions.
that's the one I bought 63-7 corvette but it flows the other way..lol http://www.napaonline.com/MasterPag...on=Positive+Crankcase+Ventilation+(PCV)+Valve
Is it a flapper or a spring? If flapper, make sure it's mounted so gravity isn't keeping the flapper open.
It's a flapper, I tried restricting it and it sure doesn't change much, I slipped a washer inside the tube and pushed it up against the pcv and it flowed the same. I also put a piece of fuel line inside the pcv nipple then the bigger tube on the outside and it still flowed right on through. I'm about ready to just switch back to the no pcv way of things at least the car ran then. I'm going to try and screw it into the oil fill tube tommorow, I know the vacuum will close it off but I'm trying anything at this point. Now with both valve cover breathers open nothing drastic should happen right ?
The pcv wins today, I had the last straw with it. I tried screwing it in the back of the carb base hoping it was more restricted vacuum than the spacer hole was. Problem with that idea was it ran right into the vacuum nipple coming out of the front of the rear carb, so off to get a street elbow. It took awhile to get it to line up so I could screw the pcv into it without hitting the carb and still being horizontal. I pulled the oil fill tube, spun it around 180 to line up with the new pcv location, threaded in a nipple to take the tube and right after that the cuss words were flying. As soon as I started slipping the hose on with a little spit on the thing for it to slide easier, the threaded bung fell right off. Nice nos e-bay purchase.....yeah right http://cgi.ebay.com/ebaymotors/1966...62QQcategoryZ34202QQihZ020QQitemZ300225043791
That sucks. I bought a new fill tube from YearOne when I worked there. They've got the one with the threaded bung on it (They actually have three different ones). Any Chevy muscle car parts source should have these. Also, I found it was worth the month popping for the "correct" fill cap. The generic cap was a Mr. Gasket, and I couldn't believe YO had it in their catalog. It was a POS--didn't even seal. For a few bucks more I got the resto-correct one, and it seals nice and tight. -Brad
Well a little over a year later I tried my luck at the pcv once again. I welded that threaded bung back onto the oil fill tube, put the elbow back on the rear of the front carb and screwed that same pcv back into it. I put a nipple back onto the bung at the oil fill tube and ran a hose from one to the other. I took it for a bonzai run and it seems to be running fine, came back and readjusted the mixture screws on the front carb but the rear needed nothing and backed the idle back down. I'll take it on a longer trip tomorrow to test it further but it seems to be just fine. The previous problems could have been caused by an internal vaccume leak in the valley. I found out the hard way the heads were cut 30 thou on the bottom but not matched on the intake side. I was leaking around the bottom of the ports but of course it didn't show on a leak check from the top side. I had the intake cut last year and haven't had a problem since. So after a year I went back and fixed the pcv, it was always in the back of my mind and the front when the vapors would appear, now hopefully all behind me.
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