Getting a new 235 togather for my 37 and its going to get a PCV system,the present 235 has the original 37 valve cover and road draft tube which I would like to retain but does not have to function. Thinking about cutting the road draft tube in half so I can block it off and weld a bung in to accept the PCV real close to the block so it will not be so noticable,now the 37 valve cover might have to go since it has no oil fill cap and will need to breath so I think I do have a later 216 valve cover that has one and if not will get one. Those 216 valve covers have vents so I will have to find a way to close them but do not want to alter the looks of the valve cover from the outside so I need to know if this plan is doable and if anyone has done it I would like to know how you done it,I do have the present 235 looking like a 216 as much as I could even with a 216 side cover modified to fit and the new 235 will be painted the original color this time.
On the 216 / old style 235 valve cover, you can braze the vent slits closed if you are going to paint the valve cover. Or, JB Weld as Fox suggested. As you probably know, you can use a later style oil fill cap that contains filter material on valve cover, as your PCV system inlet. Should work fine.
I have seen factory PCV setups with the vacuum to the valve cover. Where is the engine air intake? Others pull air into the valve cover with the vacuum line being connected where the original draft tube is. Is there any advantage as far as which way the air is pulled through the engine?
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Panic, a little more plumbing, but sure, that's even better, if the air cleaner has a port (or port added) for a vent line to the crankcase. There are closed oil filler caps that have a side port for such a line, in mid-60's Chevy's, as I recall. Wouldn't be hard to add a fitting for that to the valve cover as another option, which is what the factory RPO did.
J, shouldn't be any practical difference if the vacuum is at the valve cover, and air inlet elsewhere, or as is typically done on the 216/235/261, vacuum at the original draft tube location and fresh air inlet at the valve cover. The optional factory system had vacuum at a modified draft tube top piece, provided fresh air from the clean side of the air cleaner to a new fitting installed on the side of the valve cover, and used a closed oil fill cap. I like this a bit better than putting a PCV valve directly where the draft tube fit, since it provides additional baffling. See the image:
I prefer to have negative pressure in the engine. So I've made a dipstick which seals with 2 o-rings (fits in the stock dipstick tube) and I use an oil filler cap with a center hole into which a fitting with a reduced hole goes. When I have it choked to the point of what I think is the right engine negative pressure (positive pressure encourages oil leaks) then it goes to a hose which in turn is filtered. On the valve cover, I have made wide spreader bars which keep that sucker pressed down tight out of aluminum...as I recall it was 3/16" thick. You can see them here. https://beta.photobucket.com/u/JonGoodman/p/9ce484b5-5a62-475f-886a-8b51a08ceca0
There are 2 of these on each side of the valve cover reaching end to end and meeting in the center.
With a 216, having vent slots in the valve covers, I would not bother with rigging a PCV setup. Your engine will be just fine without it as long as you change your oil every 3,000 miles and seldom drive on dirt roads, or across hay fields all day long. Someone posted a few years ago that they closed the vents, added a PCV setup to draw air from the modified down draft tube, to the intake manifold, only to find out that white creamy deposits formed on the underside of the valve cover. This creamy deposit is caused from steam which normally wafts out of the valve cover vents, but is now collecting on the underside of the valve cover since it cannot get out any more. A better PCV setup (if one 'must' have one) in my opinion would be to pull air through a positive crankcase valve installed in the top of valve cover, going to the intake manifold windshield wiper port. Then you will need to provide a fresh air source from the center of the air cleaner, going to the modified down draft tube. To recap: Crankcase fumes are sucked out of the top of the valve cover, into the intake manifold. (This solves the accumulation of white creamy deposits on the inside of the valve cover from steam due to closed vents.) Clean air is drawn from the center of the air cleaner, down through the bottom of the block via the modified downdraft tube. Carl