aero3113 Posted March 4, 2011 Report Posted March 4, 2011 All of my fittings are air tight for my PCV system except where the oil fill cap and tube fit together. I can seal it with a strip of tacky window sealer around it but was just curious what others have done. Quote
randroid Posted March 4, 2011 Report Posted March 4, 2011 aero, I haven't gotten around to installing a PCV setup on my '48 yet but the ones I've seen have a hose running from the cap to the air cleaner. Somebody will surely add the details for you. -Randy Quote
aero3113 Posted March 4, 2011 Author Report Posted March 4, 2011 (edited) Yes,I have a line from the cap to the aircleaner but where the cap and oil fill tube meet it is not air tight. Edited March 4, 2011 by aero3113 Quote
JBNeal Posted March 4, 2011 Report Posted March 4, 2011 I've been mulling this aspect of the PCV system for awhile, and I kinda figured that this doesn't necessarily have to be airtight per se. Power Wagons that came with the PCV system had a solid oil fill cap with a gasket. I reckon if your fill tube opening is round (except for the original cap index), and your cap fits tight with metal-to-metal contact on the fill tube, then any air entry is highly restricted, kinda like trying to breathe through one of those coffee stirrer/straws. In time, I reckon a little oil film will appear in this area, and this film might cake up with dirt, effectively sealing off the cap. Another idea is to use a layer of super-thick axle grease on the cap ID. I've used the thick axle grease trick on lawn tractor rims to seal off leaky tire beads, maybe this could work on the oil filler cap. Quote
aero3113 Posted March 4, 2011 Author Report Posted March 4, 2011 Could you find or fashion a sheet metal cap, drill a hole for a barbed fitting, attatch the fitting, then use rtv to seal the cap? Or just cut a circle of sheetmetal to cap the tube, fit the fitting and weld it to the top of the tube. That would be the best way,but then I wouldn't be able to get the cap off to put oil in. Quote
Alshere59 Posted March 4, 2011 Report Posted March 4, 2011 (edited) There are two types of PCV system open and closed. A threaded or sealed cap would be closed naturally. The schematic referenced for our engines are open. A nipple is attached to a fill tube for the hose going to the air filter. The cap would be the factory one. I purchased a cap from NAPA that is close to the same style and has a fitting for the hose to the air filter built in. I will see if I have a part number if you want. If you want a closed system, seal the filter at the base of the cap. I had to swap fill tubes from another engine that was round. I think it was this one. http://www.napaonline.com/Search/Detail.aspx?R=BK_7031669_0299311797 Edited March 4, 2011 by Alshere59 Quote
Powerhouse Posted March 4, 2011 Report Posted March 4, 2011 When I had th pcv hooked up on my old engine I used an oil cap from NAPA that had a short tube on top of it to attach a hose to. The one I got was for a mopar..and even had made in U.S.A. stamped on the top. I have seen these type of caps available at many parts stores...in the performance section...usually chromed. They even come with a couple rubber grometts to seal of the are in between the filler tube and the oil cap. Quote
aero3113 Posted March 4, 2011 Author Report Posted March 4, 2011 I did seal my cap with epoxy a while back that is not the issue,its just air getting in between the cap and tube. Won't that create a vacume leak? Quote
Powerhouse Posted March 4, 2011 Report Posted March 4, 2011 Yes, it would be a leak...but it wouldn't really matter much if ti's a small leak. The seal is broken inside the air cleaner anyway, which makes me wonder why a path is needed from the oil cap to the air cleaner anyway...wouldn't it just filter through the caps filter material anyway. Quote
blucarsdn Posted March 4, 2011 Report Posted March 4, 2011 Some background on Positive Crankcase Ventilator's: Prior to the mandatory application of PCV's in 1963, crankcase ventilation mostly relied on gravity ventilation via a "road draft tube" and a cap on the oil fill tube. The PVC eliminated the draft tube, in it's place a closed circuit drew air via vacuum through the oil fill cap, the crankcase, and them into the intake portion of the carb system. This system eliminated the engine blow by into the environment and thereby eliminating approximately 95% of the pollutants. I have converted the majority of the antique vehicles I have owned for the past forty years to closed crankcases utilizing PCV. The short list would be '57-60 Ford Y blocks, early CSB's and OHV 6 cyln's. I have never done a Mopar flathead, however the application would be the same. Since all flathead six's all have side covers for the valve lifters, and a road draft tube that allows blow-by to exits the block, the addition of a PCV would require the removal of the draft tube and the use of a fitting in it's place to attach a hose leading to a vacuum port with a PCV valve in the hose... NOTE!! A BAFFLE WOULD HAVE TO BE FABRICATED ON THE INNER SIDE OF THE SIDE PLATE TO STOP OIL FROM BEING DRAWN INTO THE INTAKE HOSE. A breathable filler cap would be used on the oil fill tube. In many cases the carb would need to be leaned out because of the added oil vapor... The blow-by vapor will also act as an upper cylinder lube. I keep my eyes pealed for '63-65 CSB's and '64 Ford Y blocks so I can harvest the fitting's that were used to replace the road draft tubes on those early engine. When selecting a PCV valve, select one that closely matches the CID of the engine you are working on. The size of the valve is important because it must snap closed on acceleration in order to provide vacuum for the distributor advance. Quote
TodFitch Posted March 4, 2011 Report Posted March 4, 2011 Yes, it would be a leak...but it wouldn't really matter much if ti's a small leak. The seal is broken inside the air cleaner anyway, which makes me wonder why a path is needed from the oil cap to the air cleaner anyway...wouldn't it just filter through the caps filter material anyway. I think it was supposed to work both ways: Under "normal" conditions (engine in good shape) air is always drawn into the pan through the cap and thus through the carburetor air filter. For that you could get rid of the hose and just use the filter media in the oil filler cap. And that is what the early PCV systems did. However if the engine is worn and you are under full throttle, then may be more blow by than the PCV valve will allow back into the manifold. So the excess blow by comes up the filler tube, through the hose and sucked through the carburetor to be burned. Quote
Alshere59 Posted March 4, 2011 Report Posted March 4, 2011 (edited) I did seal my cap with epoxy a while back that is not the issue,its just air getting in between the cap and tube. Won't that create a vacuum leak? Yes a PCV valve is supposed to be a controlled vacuum leak. Not between the cap and tube though. The cap I gave earlier will seal between the tube and cap as it has an O ring. The one I got has no vent to the outside just some filter material for the tube. My tube was round so it sealed well. This gives a whole lot more info. on operation if needed. Edited March 5, 2011 by Alshere59 Clarity Quote
Guest bewillie Posted March 5, 2011 Report Posted March 5, 2011 Why do you have to change air intake? Just install PVC to vacuum and ride. Quote
thrashingcows Posted March 5, 2011 Report Posted March 5, 2011 (edited) I was researching this one night a while back, and came across a thread, and post, where someone used a long filler tube from a 90's Magnum V6/V8. It then had the twist on cap for an relatively air tight seal. Here's the thread...I had it saved in my subscriptions.... http://www430.pair.com/p15d24/mopar_forum/showthread.php?t=21120 Post #48...and others...show what was done. Edited March 5, 2011 by thrashingcows Quote
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