The Stovebolt Site Forums The Shop Area Engine Shop PCV for a 1959 235 using an Offy Valve cover

I bought an Offenhauser Valve cover for my 1959 Chevy 235. My question is how to route the PCV lines. The current setup has two lines coming out of the valve cover. One is for the air cleaner, and one is for the intake manifold. The Offy valve cover has only one opening to draw from. Can the flow be split to both locations coming from the oil cap with a breather tube?

I don’t splitting the one connection at the valve cover would allow the PCV to work properly.

You need two openings. One for the PCV to “suck” with the power of manifold vacuum. Another for some means of providing filtered makeup air. Lots of ways you could skin that cat.

I’d probably use the existing valve cover hole to make your PCV connection to manifold vac. Find another place to provide the makeup air.

If you do a web search for “valve cover bulkhead” you will see a number of options for creating such an opening. That could be drilling a different spot in the same valve cover, or perhaps in the push rod side cover……and connect your air filter nipple to that.

Here’s one option I have looked at:

https://www.jbugs.com/product/9164.html

I took a different approach. PCV is located in the front mounted oil fill position. Attached a round, motorcycle-style filtered breather to the outlet of the draft tube. Crankcase vapors pulled from the top, clean air delivered back to rhe crankcase via breather.

Is your oil fill cap vented? Thats what I did to my 59 235.

rangerd, 1st off Welcome to Stovebolt! Guessing you aren't interested in adding extra holes to your Offy valve cover just in the interest of adding a port for a PCV valve??? If so, you may want to locate (or fabricate) and install a PCV setup that uses the draft tube and intake manifold ports on your 235 as you can see was available as an RPO option in the extract below from the 1955-59 Truck Factory Assembly Manual.

This is what Gdads factory recommendation would look like, they did the engineering for us so why reinvent the wheel

The oil filler neck with outlet is available, ordered an early corvette v8 filler neck and cap, or make one out of the stock draft tube

https://www.stovebolt.com/ubbthread...0s-engine-with-non-pcv-valve-covers.html
Is a previous discussion in this with more info and pics

Hanks c ... it's so helpful to have a real image to go along with the drawing. Thanks. Hope the OP also finds it useful.

Modified road draft tube to accept rubber grommet & PCV valve.Steel line to intake manifold. Breather hose from valve cover to air cleaner. Closed PCV system.

BC59, how does your engine get fresh airflow into the crankcase? The system you describe in your photos doesn't look like it would accomplish that. Wouldn't the hose from the air cleaner to the valve cover draw air out of the engine? It seems like the carburetor, which is drawing air into the engine would just suck air out of the valve cover.

The vacuum produced at the PCV is far more powerful that the air pressure on the "clean" side of the air filter. There's no vacuum way up there, at least unless the filter element is so clogged that it causes the carburetor to flood. Modifying the road draft tube like the one in the picture without puttong the PCV up close to the height of the valve cover like the factory setup does might make the engine an oil-burner, however. There's usually a good reason the factory does something, not just spending money on a different dsesign for no reason.
Jerry

O.E. design of 261 had screw in PCV valve at same location with pipe going over the top of valve cover to intake manifold.
Filtered air enters via stock tube on 261 valve cover with hose to clean side of air filter.
No issues with oil being drawn into intake.
Note: vented cap can be seen in 1st pic (open system), second pic has sealed cap, fresh filter air via tube on valve cover (closed PCV system).

Oil fill cap on the valve cover with a PCV port built right in the cap?

I don’t have one in front of me, but I believe the factory 261 setup does put the PCV a fair bit higher on the engine than the retrofit draft tube does.

From 60 shop manual
Note pipe coming over the valve cover that connects to the intake manifold, no valve. The other end goes into PCV valve.
Note fresh air hose from air filter housing to connector on side of valve cover.

The factory setup has an extended draft tube that puts the PCV at least 6 inches above the top of the road draft tube. That's to minimize the tendency to pull liquid oil out of the crankcase, instead of just vapors. There's one really stupid design out there that involves putting a freeze plug into the road draft hole with a rubber grommet in it for the PCV. That's a guaranteed oil burner situation.
Jerry

Here is the factory setup that replaces the road draft tube.

Good pics. Doesn’t look to me like it would be hard to fabricobble the PCV setup from a draft tube. Lop off the piece that turns and goes down. Braze some sort of threaded fitting in there. Add a piece of bent pipe to the bottom.


Phak1 - is the hard line 3/8? Looking at pics of the correct part #….seems like the original style PCV valve is pipe thread on one end and female flare on the other.

I used 3/8” CuNi for the tubing. I had to get creative making the connection from the OEM PCV valve to the tubing and likely you will too.

Here is the post on the installation.

Good info, Phak1.

Looks to me like you can source a tube nut for 3/8 tubing that has 11/16-18 thread. Would that have simplified the connection? Or is there more to it than that?

This is the stock set up on Doughboy. It’s got an updraft carb.

13/16” inverted flare is for 7/16” tubing which is the stock size. I couldn’t find 7/16” tubing so, I opted to use 3/8” which is readily available. At the time, I couldn't find a 13/16” inverted male flare to 3/8” tube fitting, thus the reason for fabricating one.

If you have a source, please post it so others can benefit from it.

I just cut off the downdraft tube and inserted a common grommet (bought it at Auto Zone or O'Reilly's). At the top of the copper tube I inserted into that I used a 1/2 to 3/4" plumbing adapter and into that inserted the PCV valve. Then I bought a generic non-vented oil filler cap with a grommet and used a 1/2" copper plumbing outlet into which I inserted rubber hose which goes to a nipple under the air cleaner (for the clean air source).

Nice closed system Jon!

I was going by this post in your earlier thread:
“Phak1: I received my NOS PVC valve (AC-469) today. The threads on the inlet side are 1/4” male NPT and the outlet is 11/16”-18 female inverted flare. Thus the reason for this post.”

I pictured buying a few adaptors and installing CuNi tubing to make the connection. Well that seems to be much easier said than done, as “No1300” found out, and I am finding out…...“
–––––––-

I CAN locate an INV flare tube nut which has 11/16 thread and fits 3/8 OD tube. Are you saying you need a fitting that is 13/16 thread and fits 3/8 tube?

Thanks BC! I think it cost me about $15 total. I use an air filter I got from an old slant 6...

Jon G, Is that slant six air cleaner sitting on a carter YF? No adapters needed?

Yes, it sits right on top of the YF3211. I made a gasket for it, but the slant six it came from had a one-bbl and it was the same size. Still plenty of FRAM filters available for it and a few years ago Amazon had them on sale at $5 each shipped so I bought about 6 of them.

i would like to have a factory PCV valve as supplied on 261s. I believe this discussion has come up before but I don't remember the outcome. I suspect the part number on the valve I have has been superseded but I haven't found on by the original part number of by application does anyone have a source?

Mine draws too much air and I can't get the idle speed down below about 1,000 RPM so I went back to the road draft tube. Does either raising or lowering the spring tension change the amount of air at idle? My old one appears to have the correct spring tension according to the manual. It's probably worn so it leaks and I done 't know what a new one looks like.

I believe the OEM valve can be disassembled for cleaning. You might want to try lapping the plunger where it seats against the body of the valve to make sure it can seal well when idle vacuum is applied. Chances are there's a constant leak that shouldn't be there, which is causing the idle speed problems. A weaker spring might help- - - -nothing says you can't do some tinkering to try to improve things. Also, check the throttke plate in the carburetor. Some of them have an air bleed hole in the flap valve that can be plugged with a pop rivet if the idle speed is too fast.
Jerry

For what it may be worth, I've found the Standard Parts PCV valve V237 to work well on the 235...especially one with good vacuum and compression. I tried several types in the process. Whether the valve in the 261 was different I can't say.

Jon: I found this picture of a V237 on ebay.

I assume a hose slips over the metal end. Is the metal end connected to the intake manifold or crankcase?

Why are there two plastic ports?

Big metal end goes into the grommet in your valve cover, or breather, however you’re setup. Plastic barbs are hose hookups to manifold vacuum. I don’t know why there are two of them on that particular valve. I run one like that in a non vented valve cover breather. Might has only one barb.

I think I’m running a Fram FV191.

One port on the PCV valve is connection for an evap system / charcoal canister (if applicable--which I doubt anyone here would have). Please leave it plugged. In my case I cut off my road draft tube about 2 inches from the junction, inserted a very common grommet there, inserted a piece of 1/2 inch copper tubing soldered to an L fitting, ran that up to the level of the valve cover, soldered a 1/2 to 3/4 inch copper tubing adapter and my PCV gets two o-rings and fits nicely into that. You probably can see the black 0-ring in the image below. I used some common metal I had to make a piece connecting the tube back to a valve cover screw for stability. The tube from the PCV valve goes to the intake manifold and then I used a non-vented filler cap with a grommet for the other tube and ran it to the clean side of the air filter (underneath...I put a nipple under there for it). Please see images below and let me know if you need more. The PCV valve I use will pull between 1 and 2 in of vacuum and that's about perfect for evacuating the crankcase and keeping a bit of negative vacuum in there. More than that won't be all that good.

Jon, that's a very well-engineered installation. It puts the PCV valve high enough above the crankcase that there's no danger of pulling liquid oil into the intake, only vapors. That extra nipple on the PCV could be used to operate a vacuum gauge on the dash, since it's getting full manifold vacuum. It's a real education, watching how small an increase in throttle position it takes to open up the power valve in a carburetor- - - - -"Goodbye, gas mieage!"- - - - -especially with an OD transmission onboard!
Jerry

I just Amazoned the V237 PCV valve for under $3. My system evacuates at the top center of the valve cover and gets replacement air at the top of the oil filler which has had its draft tube cut off and plugged. Sort of backwards to the air flow on Jon's. I'll let you know how it works.

Thanks Jerry...I've actually always thought the PCV setup caused it to run a bit more lean than rich. One of the PCV valves I tried (particularly at idle as you would expect) caused it to run notably too lean.

I was referrinjg to lugging the engine- - - -even a little bit- - - -which causes the manifold vacuum to drop precipitously- - - - -causing the power valve to open and run full rich. People get so hung up on OD transmissions and low RPM at cruuise speed that they totally ignore the advantages of letting the engine rev and keeping the manifold vacuum high- - - -the way the engineers designed it to do. The timid souls with lace on their drawers are so afraid of a little fan noise that they're willing to sacrifice 3-4 miles per gallon so they don't have to listen to it.
Jerry

One of the reasons I let a vacuum gauge guide me while driving.

Well said Jerry!
It's just fuelish to be cruzin along with low manifold vacuum.

One theory about low RPM and attendant low manifold vacuum is that pumping losses due to carburetor butterfly valve restriction are minimized. That could be negated by richer mixture at low vacuum. But the mixture can be adjusted to compensate.

Most old gas truck engines that I drove when under load ran at about 0" vacuum nearly all the time. The GMC 270 and the 302 didn't even have vacuum advance on the dizzy. That said they also got terrible gas mileage but we're talking a 270 pulling 26,000 lb loaded dump truck and the 302 was a hay shaker. They weren't fast either. An exception I can think of was a '52 Ford F8 tractor with a 332 Lincoln V8. It was set up to run about 2400. pulling a load of hay at 46,000, not exactly a Hot Rod Lincoln but it did have a 4-barrel carb and dual exhausts. It got slightly better mileage than the 302GMC and was slightly faster. On the Ford, the boss wanted us to hold 4"Hg. That was hard to do; one eye on the vacuum gauge and one on the tach, third eye on the road. We also had an I-H truck and trailer rig powered by a 1090 Hall-Scott I-6. It pulled 72,000 and had 2 updraft carburetors, dual ignition, and overhead camshafts. It had lots of power and got about 2 MPG pulling hay over the mountains. It was also set up to pull about 1800-2100RPM. I don't remember if it had a vacuum gauge but the carbs set up quite a howl at 2100 RPM full throttle. It was enough faster than the other trucks that we could unload the same day and make a trip a day.

Engineers also factored in specific fuel consumption to their designs. Specific fuel consumption is pounds-of-fuel-per-horsepower-per-hour. That minimum occurs just below peak torque. So the least fuel consumption would occur at 0" vacuum at about 1800 RPM on these engines rated at peak torque at 2,000 RPM. So the carburetor would be set up for maximum torque at 0" Hg. A

Camshaft design also plays into this equation. Most 235 cams provide peak torque @ 2000 RPM, 261 cams @2200. Fuel consumption on my 3800 with 235 dropped a lot when I went to a cam with peak torque at ~2600 RPM. That is because for highway usage I was running 2800-3000 RPM, WAY above peak torque and at least 1,000 RPM above minimum specific fuel consumption. I made no other changes and went from about 9MPG to about 13MPG. Then came ethanol laced gas and I was back to about 10MPG.

When I put in the 261 the compression bumped up from 8:1 to 9:1 and the displacement up by 11% to 261 and I re-geared it from 5.13:1 down to 4.57:!. Same cam. It now cruises comfortably at 62 to 65 MPH as compared to 58MPH and the mileage is about 10MPG up hill and down dale, even into the wind. But with a tail wind it'll jump to 12. It now gets about 12 empty, i.e. no camper. I think mileage would be better with a 4.88 gear rather than 4.57:1. That would put RPM at 2800 rather than 2600. I notice that the fire tends to go out below 2500.