The Stovebolt Site Forums The Shop Area Engine Shop PCV valve

We have a '54 235 with solid lifters and a '61 235 with hydrolic lifters. The '61 has the whole in the manifold for the PCV valve conversion, the '54 does not. We know the basics of the installation but do not know which valve to use.
NAPA has a valve listed for a '62 chevy engine which we think will work. However, we do not know which valve to use with the '54 engine. Anyone have experience with this situation? Is there anything in print? Any help is greatly appreciated.

The same PCV valve (GM # 1544935) was used from 1949 through at least 1960 on non Dubl-Duti (non Forward Control, step van) trucks - on all size 6-cylinder engines. If you have an original PCV set-up, it would seem to be a good bet that the 1962 235/261 valve should work OK on the 54 engine.

I have seen only a few GM Chevrolet truck PCV systems up to 1960. I do not recall a connection to a manifold (" . . the whole in the manifold for the PCV valve conversion . . "). There was PCV plumbing connected to the air cleaner, and to the valve cover, and to the road-draft-tube replacement PCV tube.

Your 1961 235 might be a truck engine that was converted to using hydraulic lifters; or, is you engine an automobile engine? Did automobile 235 engines have a PCV option in 1961 (that option is not shown in the 1960 car Shop Manual)?

Do you have a photo that you could post of the PCV parts?

What is the NAPA part number for that PCV valve?

Hi, Thanks for getting back. Your working with an apprentice. The 1 ton panel has the '61 engine with hydraulic valves and the hole in the intake manifold. "Engine vacuum draws harmful vapors through crankcase ventilation into the intake manifold." (April 2011, Vintage Truck Magazine, Crankcase Ventilation by Bob Adler) Everything you have stated about the PCV plumbing is what his article says and shows. Then the PCV valve is on the replacement PCV tube with a tube that crosses back over the valve cover to the intake manifold.

The engine and 3 speed transmission with overdrive came in the truck when I brought it and I do not know the history. However, it looks as if an engine blew or a blade from the fan punched a hole in the right side of the engine compartment. We're (the mechanic and I) are guessing the engine and tranny were taken from a '61 automobile and put in the truck.

According to the article "Chevrolet started offering PCV valves in 1948 on its forward-control parcel delivery vans. In 1950, it offered a retrofit kit for all 1949 Chevrolets." It also states, "The draft tube's last gasp on Chevys was 1962."

It also states "Some sources say GM invented the PCV valve for use in Army tanks during World War II." So they could ford deep water.

The NAPA parts number for the '62 valve is 2-9215. I also need to look for the replacement PCV tube to replace the road draft tube.

The '54 engine is in our '54 3100 and appears to be the original block. It doesn't have the hole in the intake manifold.

I didn't realize the Bob Adler includes his phone number and e-mail address in the article until I referred back to it today. I will try contacting him for more info.

Unfortunately I am not computer smart and do not know how to do photos.

Bettyann

The PCV valve grew from necessity. An military application was probably the main cause. When the civvy 216 and later truck 235 low pressur engines were used in military/battlefield conditions the practice of using draft tubes and vents cut as intake on the valve cover just behind the acorn nut holding the valve cover became a problem...... first dust in North Africa than water seapage during beach landings. Well beach landings could be dealt with using temporary putty to seal the engine covers, battery caps and battery poles,etc..... but usually the putty was to be removed ASAP upon landing. I think the North African campaing may have been the major contributor.

Early attempt by GM Canada for CMP military application was to stop punching the vent slits in the valve cover and installing a fancy miniature oil bath cleaner on the valve cover... this dealt with the air intake to the crankcase then they removed the draftube and retained just the vertical part of the draft tube with the top part sealed crimped in place instead of the oil filler cap that the civvy model had.

Then came the PCV metal two piece that could be serviced by unscrewing the top/bottom part and cleaning up the inside plunger and spring. This PCV setup was hard plumbed from the side of the new sealed draft tube to over the front of the valve cover to the intake manidold just under the carburator. Thew actual PCV valve was located vertically jusy below the carb entering at 90 degrees into the square penum chamber.

Now for finding these PCV valves.... identical model, all steel, were used on WW II Jeeps..... and most Jeep parts supplier shops will have them in stock..NOS...for about $25.... check Peter De Bella as a Jeep supplier.

You now have the birth of the PCV valve set up very similar to what I found on a 59 261 with solid lifters and 4 speed...... which has since been rebuilt and sitting in a 1940 Canadian Military Pattern cab 11 1940 RH drive 4x4 truck.

I would love to illustrate the above with my pictures but find the posting difficult unless I can send them to a memebr who will post them for our readers.

Bob C.

If you mail photos to me, I'll post/host them (click my name to the left, to get my email address.

Thanks for the correction on the connection to the intake manifold (below the carburetor, on the outside). Did the later PCV set up look like this?

Thank you guys, really appreciated. Tim, the picture you provided of the PCV set up is the same PCV set up as the picture in the magazine article.
Bettyann

Will email you Tim.

The shop manual photo you have is exactly waht I had on my 1959 261 3 ton fuel truck with 4 speed tranny. The PCV shown is exactly the same as used on Mil. Jeeps.

Thanks for your help.

Bob C

The last ones I bought from Peter DeBella appear to be more cosmetic than functional, unless I'm missing something. When held up to the light, it is possible to see through it (and suck or blow both directions). The Debella part has Willys part # WO-A6895 and Ford part # FM-GPW6769 on the box and AC1543018 and ORDN A-336400 stamped into the body of the PCV valve.
I have also got a couple of (NOS from e-Bay) AC PCV valves that are labelled as CV476 or 5647235. They appear identical except that the AC476 valves are silver instead of black and the internal plunger isn't through drilled so they do seem to be more or less a one way valve.

I have a 1955.1 with 235 and pvc system as described above. It is a factory installed unit and the valve cover is routed to the air cleaner. I checked the pvc valve and found it was missing the spring. I located another valve on eBay and as it was 40 plus years old it took me a while to get it open. It has a spring so I placed it in my pvc valve. I was getting some smoke out the exhaust and checked the compression on all cylinders and they came to 120 constantly. So I figure rings are good but still get smoke when decelerating and some at idle. When accelerating there seems to be no smoke. Not sure what could be causing this issue.
Any thoughts would be helpful.

A PCV is not a one-way valve and never completely closes. A tapered cone moves in & out of an orifice (sized for engine displacement) balancing engine vacuum against an internal spring. It should rattle when shaken.
At high vacuum the cone retracts, allowing full vapor passage. At WOT the vacuum drops and the spring moves the cone tip deeper into the opening and restricts flow.
If you can't find the right one, a PCV from a similar engine such as the Gen-3 230 or 250 should be close enough to work.

Have a look at this thread: https://www.stovebolt.com/ubbthreads/ubbthreads.php/topics/1422635/235-stand-pipe-pcv.html

You can try hooking up a vacuum gauge to investigate the smoke issue.

I recently saw an old thread where Jon G described his PCV. Sounds like a non vented oil fill cap with a grommet in it….plumbed straight to the air cleaner. Perhaps he can pop in here and correct me or provide more detail.

That is exactly how I did mine. I'm away for 2-3 weeks and don't have the image files, but essentially I made a seal for the dipstick (a couple of o-rings), I used an oil fill cap with a central grommet (which is exactly the same ID as the OD of a 1/2 inch copper elbow, put the elbow into the grommet and then ran the hose from there to the underside of the air cleaner where it will suck filtered air back into the engine (via the oil filler cap). I hooked the valve up to a cut-off and plugged breather tube. If I recall, I'll send images when I return mid-December. The oil filler looked like this one:

tinyurl.com/muy29ku8

You plugged the PCV valve into what portion of the setup?

And you kept the inlet on the air cleaner to the “dirty” side of the air filter…am I understanding that right?

To have a "closed loop" system, inlet air needs to come from the clean side of the filter. Some modern air cleaners have a small horsehair style filter in the side of the housing for crankcase inlet air so a manufacturer can technically call the system "closed". Some people cut the road draft tube off and weld a washer in its place for a grommet that holds the PCV valve. OEM standpipes put the PCV up around valve cover height to keep liquid oil from being drawn out of the crankcase.
Jerry

Here's where a picture (image in today's world) is worth 1000 words. The PCV valve goes into the modified downdraft tube. Actually I extended a length of copper tubing up from it (3/4" tubing as I recall, but could have been 1/2") and that is where the PCV valve goes. A couple of O-rings seal it well. Then the tube from the PCV valve goes over to the intake manifold threaded hole (same place the vacuum wipers might connect or a power brake booster if you had one). This allows the engine to suck any crankcase vapors directly into the manifold, creating a small but constant crankcase vacuum to be present. Please remember the dipstick is also sealed. What we want to do is have as tight of an engine as possible and let a slight internal vacuum help discourage any oil leaks. Then from the oil fill cap on the valve cover, the hose goes over to the clean side of the air filter where clean (filtered) air is drawn back into the engine through the oil filler cap. Since there will be air sucked out of the engine constantly, we want it replaced with clean air. Also, please remember the ID of any fitting you use will determine the vacuum present inside the engine. Let's say your hose between the oil filler cap and air cleaner is 1/2" outside diameter and 5/16" inside diameter but you use a 5/16" nipple connector which has a 1/8" inside diameter. That 1/8" nipple connector will reduce (throttle down) the air flow by a bit more than 75%...area of 5/16 ID being .0767 sq in and area of 1/8 being .0123 sq in. So it is a good idea to hook up an accurate vacuum gauge to see just how much vacuum you're getting inside the crankcase. My opinion is about 2 inHG in the crankcase is ideal. Some things won't likely seal up ideally (oil pan gasket, side cover gasket, valve cover gasket), but if you straightened these before installing and used good gaskets/sealer, you should not be losing much vacuum there.

Jerry makes a very good point. The extension tube I mentioned (and made) takes the PCV valve up to a point level with the top of the valve cover...which is where it ought to be in my experience. I tried the valve at a lower point and what it did was suck up just enough oil vapor to foul the PCV valve and keep it from working correctly. What I ended up doing was to stick a grommet (available at O'Reilly's) in the hole where the downdraft tube connected and brought a copper tube extension up from there. A picture will help clarify this.

Ok, that’s different than what I assumed from the one pic I remember of your system.

I thought you were getting vacuum directly from the air cleaner (Venturi effect?) and the pcv was in between those two. And I assumed you were getting makeup air elsewhere (like a filter jammed in the draft tube?)

If someone cut a retired road draft tube canister open they would find a series of baffles meant to separate the splashed oil from the crankcase from the blow-by gases and condensation the PCV is intended to eliminate. As an engine wears and more combustion gases find their way past the piston rings, the PCV can begin to ingest oil and other contaminants it's not supposed to handle and become restricted, or clogged. At that point, the only exit vapors will have is through the fresh air intake pipe, resulting in an oily residue collecting in the air cleaner housing. On a badly worn engine from the mid-1970's with that faux filter in the air cleaner housing, I've found half an inch or so of oil accumulated in the bottom of the housing and actually being sucked through the paper filter element. Those engines could put a mosquito fogger to shame with the blue smoke from the tailpipe!
Jerry

The other thing is to use the right PCV valve. There were 4 valves I tested when I was doing this. Two were worthless as they allowed too much vacuum pull-through. Two were ok, but one clearly was the best in my opinion and one only allowed a bit less than 1 inHG. Unless you're mounting the PCV valve too low, I don't think 1 inch is enough. I'll try to remember to post the make/number of the one I used...probably should have posted that here, but didn't. As I said above it is sort of a balancing act. You need to check the valve after you have everything in place to make certain it is doing what you want.

flyn 55 Be sure oil level is right then look at valve guides and intake valve seals,also check for excess rocker arm oil,rod bearing throw-off from too much clearance is possible too. probably not bearings if no smoke on acceleration. Smoke on deceleration points to valve guides.