PCV Valves are not all equal

[Joe R.]

Working on my 67 327/350 L79 engine I was replacing the hose from the Carb to the PCV Valve /Oil Fill Tube and noticed that the hose id was smaller than the PCV connection nipple, it could be forced on but is a tight fit. Checking further I noticed the PCV valve was a CV- 590C, checking with parts catalogs it should be a CV-726C. Looking further into it noticed checking the CV-590C check valve operation it seemed to be checking in the wrong direction.
My understanding of crankcase ventilation is the hose connects to the carb and the manifold vacuum sucks the fumes from the crankcase through the PCV into the carb to be burned in the combustion cycle.
I ordered a CV-726C PCV and when it arrived sure enough the nipple was the right size but more importantly the check is going in the right direction. My guess is that someone years ago had a CV-590C PCV on the shelf and just put it in thinking it was just the hose connection difference which could be forced on, not knowing the check operation was backwards.
So now my 327/350 is breathing a lot better.
All PCV valves are not created equal.

[Edward J.]

Re: PCV Valves are not all equal

Joe, I know that my 63 SHP has a CV590C. and also I think the F.I. had this number to.

[Frank D.]

Re: PCV Valves are not all equal

My 63 also has the CV590C - There is also a 590 with no "C" which works as well. I bought a junk 63 carb and as a bonus it had a 590 original valve on it.

The repros are junk....which is why I have originals..

[Joe R.]

Re: PCV Valves are not all equal

I think where the pcv valve is located is key on the carb the cv-590 work well on the oil fill tube it has to be a cv-726c.
I just thought it was interesting I did not see a lot of info on the web on the differences in the two valves. They can and have been misused.

[Joe L.]

Re: PCV Valves are not all equal

Working on my 67 327/350 L79 engine I was replacing the hose from the Carb to the PCV Valve /Oil Fill Tube and noticed that the hose id was smaller than the PCV connection nipple, it could be forced on but is a tight fit. Checking further I noticed the PCV valve was a CV- 590C, checking with parts catalogs it should be a CV-726C. Looking further into it noticed checking the CV-590C check valve operation it seemed to be checking in the wrong direction.
My understanding of crankcase ventilation is the hose connects to the carb and the manifold vacuum sucks the fumes from the crankcase through the PCV into the carb to be burned in the combustion cycle.
I ordered a CV-726C PCV and when it arrived sure enough the nipple was the right size but more importantly the check is going in the right direction. My guess is that someone years ago had a CV-590C PCV on the shelf and just put it in thinking it was just the hose connection difference which could be forced on, not knowing the check operation was backwards.
So now my 327/350 is breathing a lot better.
All PCV valves are not created equal.

Joe------


There exist a large number of PCV valves. One MUST use the correct valve as specified by GM for any given application. The CV-590C has NEVER been a correct valve for any 1967 Corvette.

[Joe L.]

Re: PCV Valves are not all equal

My 63 also has the CV590C - There is also a 590 with no "C" which works as well. I bought a junk 63 carb and as a bonus it had a 590 original valve on it.

The repros are junk....which is why I have originals..

Frank------

The CV-590C replaced the CV-590 and the 2 valves are functionally equivalent. Where they are definitely not equivalent is in what it takes to buy one today. The CV-590C is quite common and even original configuration CV-590C valves are fairly inexpensive to purchase. A CV-590, though, is definitely not inexpensive these days.

[Joe R.]

Re: PCV Valves are not all equal

Yes I agree Joe, I just wonder how many pro's who worked on that car missed it, maybe its just the way it is.

[Joe L.]

Re: PCV Valves are not all equal

Yes I agree Joe, I just wonder how many pro's who worked on that car missed it, maybe its just the way it is.

Joe-------


Here's likely the deal: the AC CV726C was discontinued more than 20 years ago. The CV-590C was only recently discontinued. So, when the valve was last replaced someone may have decided to use a then-available valve as a "substitute" reasoning that all PCV valves are "pretty much the same". That's common reasoning of a klutz.

[Frank D.]

Re: PCV Valves are not all equal

Frank------

The CV-590C replaced the CV-590 and the 2 valves are functionally equivalent. Where they are definitely not equivalent is in what it takes to buy one today. The CV-590C is quite common and even original configuration CV-590C valves are fairly inexpensive to purchase. A CV-590, though, is definitely not inexpensive these days.

I have a line on a 590 for $40 withOUT the "C" -- original and the finish looks good.
The repro valves (I went through 3 of them) caused a lumpy idle in each case....so I painted the 590C to get by for now...

[Dan A.]

Re: PCV Valves are not all equal

Of possible interest John Hinckleys post #16.

https://www.forums.ncrs.org/showthre...light=backfire