Hey gang. I have searched and read many PCV related threads. I have an understanding of how open and Closed PCV system are designed and intended to work. Now my actual setup and issues. 1979 350 block 4 bolt mains, no rear vent and baffle. Script solid valve covers. Offy 3x2 tripower intake. 69 camel hump heads. Comp cams 12-238-2 cam Oil fill tube with, side vent tube. The engine starts and idles well runs strong. Currently I have PCV valve fitted to base of center carb with hose going to side tube on filler neck, and breather on filler. When this intake was on a 283 with vent on rear of block, the hose from PCV on carb went to rear of block and it worked well. Issue: I am pushing oil out of the brand new rear main seal, and after revving engine it is sucking vapor/oil into carb and burning it (white smoke) intermittently. This engine was in a truck, but it had a 2 barrel intake, and a solid cap in the fill tube. I didn't take good notice of how the PCV was setup before pulling it, because I knew the 3X2 intake was going on it. It did run and didn't smoke. I will try a solid cap, but then there will be no way to get fresh air into the crankcase, and with no breather, I expect the over pressure in crank will be worse (blowing oil out rear main already). I guess drawing vacuum from bottom of oil fill tube with breather on top of tube, air is taking shortest route, as I was worried, but then how is the crank over pressure with an open system and how is oil getting burned in carb, if not going through PCV valve and hose. I was going to drill a hole in rear of the intake and put a grommet and PCV or nipple at the back of the engine. But wanted some thoughts before ruining a nice classic Offy 3x2 intake. Things to try: Solid cap (no fresh air intake?) Move PCV to back of intake.(Drill Offy intake!!!) Thanks guys, if anyone has similar setup, (late block, script solid covers, Offy 3x2 intake) and is not having issues would love to hear about your setup. Nitro
In addition to the rear baffle and hole, the other difference between early and late blocks is that the front of the block, where the fill tube enters the manifold, has a long tube down to the timing cover area, on the early blocks. This tube is missing in the later blocks. So, there is no oil separator for the vent tube, which is probably why it's sucking oil. One real solution would be to get some of the 1970s Vette valve covers, which have the baffles and holes for the PCV valve and oil fill, and are finned aluminum, so they look nice. They don't really match the intake etc you have, but something's gotta give. The other real solution is to get an early block, and then you can use the early parts and the crankcase ventilation system will work well. But, I expect someone has come up with some crutch solution that will let you make it work...just letting you know what you're up against, and how to really solve the problem.
I experienced your same issue on a brand new sbc, with oil seeping out of the front and rear of the pan, because I did not have my pcv system hooked up at first. Once I did, no oil issues at all. New style valve covers is one solution. On my older corvette, wanting to keep the stock appearance as much as possible, I did drill a hole in the back of the valve cover, with a line running up to and under the air cleaner for my fresh air side. I used a filler tube with a pcv fitting built in, as used on many 60''s Camaros and Corvettes, and it worked well. Here is a picture, just an idea.
One thing to consider about adding holes, is that Chevy went to a lot of trouble to make good baffles for the PCV and breather holes, both on the early style engine, and the later one with the holes in the valve covers. The factory baffles are very effective. If you don't have them, you might still have oil sucking issues.
As @squirrel said, it's hard to have proper ventilation with solid valve covers. I replaced my solid Cal Custom covers with later Cal Custom covers with proper baffles. I sealed the air intake on the early style breather caps with JB Weld. Ventilation intake is under air cleaner. It's not traditional, but it does work with later block.
I am curious about this thread because I have a similar situation. Late model block , one piece rear main, early intake with breather and no pcv that seems to leak some at the rear main although I think it has gotten better since the engine has broken in. I think those one piece rear seals need vacuum to keep them sealed. Thinking of using these valve covers that someone has put a PCV grommet in but no baffle underneath. Also I’m not sure if these valve covers will clear roller comp cam rockers. Sent from my iPhone using H.A.M.B.
@Kevin Ardinger, some baffle will be necessary to limit oil spray from being sucked through PCV. Oil fill breather may work, but I think a grommet and baffle on other cover plumbed to air cleaner, would ventilate the crankcase more thoroughly. Something like this might work as a baffle, but surely could be a clearance problem with pushrods/rockers. https://www.speedwaymotors.com/PCV-Grommet-with-Baffle-for-Breather-Caps,7332.html
I like the stock valve covers. The big block Chevy has nice big covers with a decent P.V.C. system.. The 427 came with factory painted covers. It gave the engine an all business look which I like..
Came off passenger side breather with an inline PCV to the base of center carb. Used a breather screen as a template and cut a plate from sheet metal to plug the top of the breather and epoxied any voids around the edges to seal it off. Tapped the breather high.....just below the metal block off plate. Stuffed the breather full with a stainless pot scrubber for the filter/baffle. The driver's side breather is unaltered, so tapped passenger side breather is pulling across the engine, grabbing the crankcase pressure.
On my car, I'm running a 350 with tri - power along with the old style filler tube with a breather. I have an electric fuel pump and I have a dummy high performance mechanical fuel pump that is rebuildable mounted on the engine. The dummy pump is gutted out and I have a home made baffle located between the doghouse plate and the block; no fuel pump pushrod. The outlet on this pump has a fuel line with an inline PCV valve. The end of this hose is connected to manifold vacuum. The line that formerly went to the tank is plugged. Upon casual inspection, it just looks like any other SBC with a mechanical fuel pump.
I drilled a hole for a 1/2" aluminum nipple over a web in my C3B. Made a "V' shaped baffle that got smaller in the rear (so oil could run off if needed), welded it to the web and welded the nipple in from the top. The nipple runs to an inline pcv and then the carb. I can use a copper Chore Boy scrubbing pad in the first section of hose as a filter if needed. Then I have the oil filler, a vented cap on a '78 350 with Corvette solid covers.....works good so far. I have a friend that's trying a hollow intake bolt (one bolt hole goes through on SBC motors ?)to the carb on a tri power setup. I'll ask him how it's going.
UPDATE, Put the non vented cap on. Now vac is pulling out of crank, seals not leaking any oil. No fresh air intake yet. Plan to drill valve cover and pull air through air filter. Waiting on parts local auto parts didn't have what I needed. Nitro
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