I did a search on here and found a old thread on a factory pcv valve......after reading it's to my understanding they were usually installed on large trucks and fleet vehicles. I am considering making my own PCV system for my 235......If I make a hole on the back of the valve cover for a grommet and a PCV valve. I know something will need to be done with the road draft tube. Im guessing that I'll need to leave it open to let air in there but must install some kind of filter or breather to keep the road dirt and dust out that the PCV valve might pull into the crankcase. I was thinking of a oil fill tube for an Oldsmobile engine..... if the tube is the same size ?? and installing a breather on it in place of the road draft tube. I also am considering an alternative of instaling something we use in racing engines they call an EVAC system.....It's basically a piece of 3/4 pipe welded inline with the exhaust at a 30 degree angle running downstream of the exhaust pipe to form a venturi effect... it has a screw on check valve that were on 70's ford emission systems which will connect to a valve cover breather or road draft tube via a piece of 3/4 heater hose Not sure if its good idea for an old 235 though because if it has too much blowby it'll be a smoker because all that vapor will be sucked right into the exhaust system......but I know for a fact that if there is sufficent vaccum in the crankcase it helps with ring sealing,bad valve guides/seals , and small oil leaks.......Im just lookin for a way to keep from getting oil spots in the driveway. I cant help it but im always thinking of ways to improve something. Any suggestions,feedback, or been there done that info will be appreciated. Thanks again, Leon
Good deal Thanks Ken, Im still wonderin if I should run a breather with this setup to keep fresh air flowin thru the motor??.......I know on some older 216 and 235's the valve cover has slots punched into the back them but that would allow for dirt to get pulled in........my valve cover doesnt have those slots but I can get a breather/oil fill cap combo. Thanks for the quick response, Leon
I believe that if your 235 was originally a truck engine then it came with a breather/fill cap on the rocker cover. IIRC car engines came with just a cap (no breather) that was in the center of the rocker cover (front to back). Truck engines had the breather/cap towards the front of the rocker cover. Somebody please correct me if I have my head up my a** and am wrong, but that's what I remember. Andy
Valve cover I think you are thinkin correctly..........you'd figure the trucks want to have the oil fill as close to the front as possible so one can reach it without a ladder....
PCV System (Leon , Andy Ken) Good thread ! . O.K. , the rocker box on 216 and early 235's had four slots punched in them , easy to miss until you know what to look for , it'd be nice if someone posted a pic (hint) . slotted rockerboxes ALL had non vented oil filler caps as that would have been redundant . As Andy pointed out , the differance between Passenger and Truck rockerboxes was the location of the oil filler cap hole . When you add a PCV valve , it's bad to place it right there in the block as it _will_ suck out a fairly good bit of oil . The Original PCV vlave was fitted to a special road draft tube that was sort of inverted , it went _up_ rather than down so the errant oil droplets would have a harder time reaching the valve and getting sucked in . Later on , GM figured out that placing the PCV valve up by the vacuum source (intake manifold) sharply reduced oil scavenging and the resultant smoking . If you install a PCV valve or Leon's clever venturi pipe , you'll need to install a vented oil filler cap , yes AC and others still make them , they even make nifty ones with a 3/4" hose nipple in case you want to either plumb it to the air cleaner for fresh air intake -OR- you want to simply add the PCV valve to the intake manifold's fitting and plumb from there to the oil filler cap ~ this isn't recommended if you drive anywhere dusty as the road draft tube will be the fresh air intake and it'll suck dust into the crankcase... There's also an oil filler cap that has a PCV valve grommet in it . I hope this helped ? .
PCV issues! I tried the PCV route on my 235 with the valve in the top of the discretely plugged road draft tube. Ran a 3/8 hard line around the back of the valve cover to the vacuum port on the intake. Soon discovered that the port would need to be drilled and tapped for a much larger fitting. The stock port just didn't have the volume of vacuum to work effectively. With a new rebuild and zero gap rings blowby has become a none issue. The road draft tube functions as advertised and I get no fumes into the cab. Dave
Blowby Hello, Dave what you are saying is that the 235 before you put zero gap rings had more blowby than the pcv could handle ?? Thanks, Leon
Here you go Nate. https://talk.classicparts.com/photos/showphoto.php?photo=499 Shows two of the four slots.
BlowBy & Manifold Aperture Leon ; Remember " some intake manifolds have small vacuum ports , you'll need one with the BIG threaded hole as the ID of the PCV hose needs to be 1/2" minimum . These old engine tend to have a lot of blowby anyways , Total Seal piston rings are great but so are standard rings when properly bedded in ! few are. -Nate
Rockerbox Vent Holes THANX Bill ! . For those who don't recognize it , that's the first year Corvette , the one with a 235 engine , dual outlet exhaust manifold , mitiple carbys and 261 camshaft , all factory fittment . Pop one of these in your truck and you'll be off to the races . -Nate
Blowby! Negative on the blowby during my initial trial of a pcv setup. The 56 engine was fine.....my rationale for trying a pcv system was to satisfy my curiousity. Using a well vented oil filler cap and hard 3/8"ID from the PVC valve in the draft tube top, tied into the existing 1/8NPT vacuum port on the stock intake just didn't give me enough volume of vacuum. I didn't bother to drill out the smaller fitting and tap it for a larger one. On my freshly rebuilt 1960 engine I haven't bothered with a PVC system because I haven't noticed any indication of a need for it. To me, no system is better than a system that isn't properly engineered and in itself creates or contributes to excessive crankcase pressures. If someone who has the need and comes up with a better setup, I'd be interested in taking a second look, just to satisfy my curiosity. Dave
