Stovebolt.com Forums The Shop Area The Engine Shop NOS GM PCV Valve

I believe the original steel tube from the PCV to the Intake manifold was 7/16" outside diameter. The threads on both male fitting nuts were 7/16 NF. That size tubing was not easily available to me at the time. I replaced the tubing with 3/8-inch OD having male fittings with 3/8 threads, cut off one fitting, bent the tubing to match the original shape and changed to an appropriate brass fitting in the intake manifold. For the end into the PCV valve I purchased a 90-degree hydraulic hose fitting with a 7/16 NF (-7) male inverted flare on one end and a 3/8-inch barbed hose fitting on the other. The hose fitting had a metal shield over the barbed tube that was cut off. I used a lathe but it could be cut off other ways. Then used a small fuel/oil tolerant hose to connect the pieces.

I recently abandoned the PCV system on my '62 261. It caused an erratic idle speed at all times and did not get along well with the large vacuum leak as the engine evacuated the vacuum tank for the hydrovac brakes, etc. I couldn't get the idle speed below 900 RPM and then it would surge especially when hot. I had carefully dismantled and cleaned the valve according to the 1962 drawings.

Aside from that there was evidence of oil being sucked into the manifold from it. We'll see if oil consumption drops with the re-installation of the road draft tube. I looked for a new valve but couldn't find one by the part number stamped on the valve. Perhaps the superceded number would work but I'll see how the road-draft tube works out before I go hunting.

The original PCV system from a 261 big truck currently installed on the 235 in my 1954 1300 Chevy is working very well. No oil being sucked into the intake, smooth idle and seems to have reduced oil leaking from seals. There is also less “engine smell” in the cab. Very happy with the installation. The 261 in my other truck will use the same system.

The pictures in my previous post does not show the completed installation. Changes include a rubber hose connecting the top of the oil bath air cleaner (filtered air) down to the side of the valve cover and the installation of a non vented oil cap on the valve cover. This allows clean air to flow into the crankcase and the vapors from the operation of the engine to be drawn into the intake manifold through the PCV valve.

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. An 11/16”-18 inverted flare is for 7/16” tubing. Difficult but not impossible to find but I don’t have a flaring tool for that size and I’m having difficulties locating an adaptor for this size tubing. Additionally, on the intake manifold I have a 1/4” pipe tee that I want to adapt the tubing to. So I would need a 1/4” male pipe to 7/16” tubing inverted flare adaptor which seems impossible to find.

Thinking that using 3/8” tubing would be much easier to find the adaptor fittings needed, I started searching for the adaptors. That is also proving to be difficult. I can find a 1/4” male pipe to 3/8 tubing but finding a 11/16”-18 inverted flare to 3/8” tube fitting or even a adaptor to go from 7/16” to 3/8” has produced no results.

My next thought for a possible solution would be to find a power steering fitting (11/16”-18 inverted flare) to AN connector, cut off the AN side and tap it for 1/4” female NPT. Then I can buy 1/4” male pipe to 3/8” tube (5/8”-18 inverted flare) fittings.

And of course I could try to find an original setup.

I really would like to keep it hard piped, so if any of you ‘bolters care to brainstorm, I’d appreciate your input.

Just brainstorming….

One of the PCV setups for a mid 60s 283 v8 is pipe thread on one end and a barb on the other. Could you adapt that to the manifold end, use a very short section of rubber to a length of Nicopp in a size of your choice, and then hardline all the way to the PCV riser?

Wouldn’t be totally stock appearing, but the short section of rubber would be in a pretty hard to spot.

The information I supplied on the thread size for the 7/16“ outside diameter tubing was incorrect as Phak1 pointed out. The -7 fitting does have 11/16-18 threads. If you are willing to use 3/8”od tubing you could purchase the fitting shown in the earlier post and cut off the tubing just after the 90-degree bend and weld the 3/8 tubing to it.

I was unable to find a fitting to match the 11/16-18 fitting on the original pipe so I cut the fitting off and welded a piece of 3/8 fuel line tubing with the flared nut attached. The brass fittings to connect to the manifold were not hard to find. The 3/8” tubing slid nicely inside the 7/16” tubing and was an easy weld. If you look closely at the driver's side picture in the earlier post you can see the reduced tubing size and smaller fitting near the intake manifold.

As I mentioned above, I have abandoned the factory PCV setup in favor of the road-draft tube. Yesterday I returned from a 500mi road trip with camper loaded. That's ~9,000 lbs gross. Oil consumption was nil, weather was 80ish F, oil temp about 210, water temp 180-200F. No odors and no apparent oil underneath from the breather.

Despite the success of the road-draft tube, I'd rather have the PCV working. Perhaps I can clean the oil/vapor separator can as I did with the road-draft tube a while back. But I still have to come up with a new PCV valve. The one I have has the part no. Phak1 showed in his post. It is apparently worn out. I have all the necessary fittings and hard line.

That PCV valve will come apart so you can inspect it.