What PCV Valve is this?

[William H.]

Re: What PCV Valve is this?

Hi Ron

Do you know what applicaiton/Corvette the CV746c was used on? I have a 1968 435 HP car and am confused between the 736c and 746c. Thanks if you can help me out. Bill

[Joe L.]

Re: What PCV Valve is this?

Hi Ron

Do you know what applicaiton/Corvette the CV746c was used on? I have a 1968 435 HP car and am confused between the 736c and 746c. Thanks if you can help me out. Bill

Bill------


The AC 746C was used for all 1968-69 L-88 and ZL-1 as well as 1970-72 LT-1.

The AC 736C was used for all 1969-72 except the above-referenced.

What did 1968 use? I've never determined it with certainty. My belief is that all 1968 small block and L-36 used the 736C and that late 1968 L-71 and L-68 also used the 736C. I have no idea what early 1968 L-71 and L-68 used (but I don't think it was a 746C).

[William L.]

Re: What PCV Valve is this?

Pictured are 3 different CV736 PCV valves:

Left:
"early" version, O.L.= 1.68"
stamped "AC SPARK PLUG", "TYPE CV 736C"
4 punch marks


Center:
Orig. 1969 Chevrolet, O.L. = 1.62"
stamped "AC SPARK PLUG", "TYPE CV-736C"
4 punch marks
"D" on bottom
The NOS valves in 1971 & 1972 boxes are the same.
The original valve from 1971 Chevelle is the same.

Right:
NOS in 1984 box, O.L. = 1.62"
stamped "AC SPARK PLUG", " TYPE CV 736 C"
9 punch marks
"M" on bottom

Basically I have 3 different styles of the CV736C valve.
The "early" version is totally different.

Dave

Dave
The the CV 736C valve in my very late (21683 vin and T 06 06 eng. stamp date) 67/435 is like the center valve in your picture, it has the "D" on the bottom. I am relatively sure that it is original to the car but not 100% sure.
Bill

[Joe L.]

Re: What PCV Valve is this?

NOTE: The GM parts numbers in the Chevrolet parts catalogs are TOTALLY DIFFERENT than the AIM part numbers.

I don't really remember but was the "1st version" CV736C PCV valve the solid steel type?



Dave

Dave-----


For some reason, AC Spark Plug Division PRODUCTION and SERVICE part numbers for the same part are usually different. It may or may not have something to do with packaging or labeling. In most cases, the parts, themselves, are absolutely identical (assuming the PRODUCTION and SERVICE parts were manufactured at about the same time). This part number dis-similarity goes WAY BACK with AC Division parts---to at least the 50's.

If you're referring to a machined steel version of the 736C, I don't think there ever was one. While there have been several different configurations of the 736C over the years, I don't think that any were machined steel.

[Terry M.]

Re: What PCV Valve is this?

I don't have an AIM handy (but the Altoona meet is fun), but I am pretty sure the PCV valve was installed in ST Louis. Doesn't it have a part number showing in the AIM? If so it was installed at St Louis and the body build date is applicable, and not the engine assembly date.

[Joe L.]

Re: What PCV Valve is this?

I don't have an AIM handy (but the Altoona meet is fun), but I am pretty sure the PCV valve was installed in ST Louis. Doesn't it have a part number showing in the AIM? If so it was installed at St Louis and the body build date is applicable, and not the engine assembly date.

Terry-----


PCV valves were installed at St. Louis. However, the part numbers don't tell us much since for AC Division parts the PRODUCTION GM part number is different than the SERVICE part number for the same piece. The Delco part numbers (e.g. CV-736C) are the same but those numbers are not provided in the AIM and, sometimes, not even provided in the GM P&A catalogs.

[Ronald L.]

Re: What PCV Valve is this?

Dave, somehow miss your post from last year. Yes, the original 736 was solid steel, just like the 691 valve.

There are two styles of 691 valves in solid construction, and then in late 67-8 a combined metal stamped bottom, solid top, and then the valve disappears, when the 736 replaced it.

Joe, parts were run at the same time on the same equipment, the job was set up and run per a volume requirement. When it was then only a service part, they might have been run on nights or weekends when main production demand was not as high.

Now the difference in part numbers is real simple, the box had a part number, the valve had a number, and the 'valve in a box' a different number that went to the AC service sales group. All other AC SP parts were done the same way.

[Mark D.]

Re: What PCV Valve is this?

I give full credit for the 746 in 68 and 69 solid lifter tri-power Corvettes because I've seen many in Bow Tie candidates I've judged that I had confidence were real. Typically though, it would be 736.

[Joe L.]

Re: What PCV Valve is this?

Dave, somehow miss your post from last year. Yes, the original 736 was solid steel, just like the 691 valve.

There are two styles of 691 valves in solid construction, and then in late 67-8 a combined metal stamped bottom, solid top, and then the valve disappears, when the 736 replaced it.

Joe, parts were run at the same time on the same equipment, the job was set up and run per a volume requirement. When it was then only a service part, they might have been run on nights or weekends when main production demand was not as high.

Now the difference in part numbers is real simple, the box had a part number, the valve had a number, and the 'valve in a box' a different number that went to the AC service sales group. All other AC SP parts were done the same way.

Ron------

I do not consider the 691 and early 736C valves to be of "solid steel" construction. They are a crimped together type of construction, just like later valves. The valves I regard as "solid steel" or "machined steel" are the earlier valves from the beginning of the PCV era in 1961. These valves are of machined steel construction and often can be disassembled by un-threading one half from the other (although this sort of dis-assembly is not often apparent). A typical early style, machined steel valve is pictured below.

[David L.]

Re: What PCV Valve is this?

Joe,

My terminology may not be correct but what I mean by a "solid steel" PCV valve is like the one in the photo below. It is an original 67 Corvette "CV-736C" valve (courtesy of a fellow NCRS member). Maybe the correct term should be "machined steel" when compared to the later PCV valves that are completely "stamped steel" which, I believe, debuted in 1968 or 1969.

Dave

[Joe L.]

Re: What PCV Valve is this?

Joe,

My terminology may not be correct but what I mean by a "solid steel" PCV valve is like the one in the photo below. It is an original 67 Corvette "CV-736C" valve (courtesy of a fellow NCRS member). Maybe the correct term should be "machined steel" when compared to the later PCV valves that are completely "stamped steel" which, I believe, debuted in 1968 or 1969.

Dave

Dave------


Well, I suppose there are all sorts of different terminologies used to describe something. There are probably even precise manufacturing terms for the different types of valves but I don't know what they are.

In my terminology, the valve you have pictured is a crimped-type valve. Yes, it's different in construction than the later crimped type valves but it's a crimped type valve nonetheless.

The type of valve that I pictured is what I and some others refer to as a "machined steel" or "solid steel" valve. The terminology comes from the fact that the valve APPEARS to be machined from a solid piece of steel and APPEARS as a "one piece" valve. Of course, the term "solid steel" is actually totally incorrect since the valve is obviously not solid and it's not even one piece. It's usually two pieces that are threaded together.

This style valve was mostly discontinued by about 1963 and replaced by crimped type valves.

[David L.]

Re: What PCV Valve is this?

Joe,

Pictured below is an original "CV-726C" PCV valve (black finish) from a 1967 Chevrolet truck (Flint engine stamped "V0207Y" with a block casting date "B 1 7" or Feb. 1, 1967) that I found in a salvage yard back in the early 1980's. The valve on the right is NOS, GM # 6422721, in a box dated "8-68" that is identical except for the finish (gray phosphate?). About 0.60" from the hose end is a seam, diameter is approximately 0.70". Both parts of each valve appear to be machined.

Dave

[Joe L.]

Re: What PCV Valve is this?

Joe,

Pictured below is an original "CV-726C" PCV valve (black finish) from a 1967 Chevrolet truck (Flint engine stamped "V0207Y" with a block casting date "B 1 7" or Feb. 1, 1967) that I found in a salvage yard back in the early 1980's. The valve on the right is NOS, GM # 6422721, in a box dated "8-68" that is identical except for the finish (gray phosphate?). About 0.60" from the hose end is a seam, diameter is approximately 0.70". Both parts of each valve appear to be machined.

Dave

Dave-----


Yes, these are what I describe as a machined type PCV valve. The finish did change on these valves at some point although the valves remained otherwise identical. The early finish was the black phosphate and the later finish was the zinc or cadmium. Quite a few different part numbered valves went through this same change but at different times. I did not realize that any remained black phosphate as late as 1967 but, apparently, the 726C did.

[Ronald L.]

Re: What PCV Valve is this?

David, I'd take that valve to a plater and ask them to check for zinc. You will find that the 66 67 original valves used don't have a bright zinc look as do parts in boxes.

Also - when you guys are referring to black phosphate, have you tested it for phos, could have been black oxide too.

[David L.]

Re: What PCV Valve is this?

David, I'd take that valve to a plater and ask them to check for zinc. You will find that the 66 67 original valves used don't have a bright zinc look as do parts in boxes.

Also - when you guys are referring to black phosphate, have you tested it for phos, could have been black oxide too.

Ron,

I don't understand your comment. I removed the CV-726C "dark" valve on the left from a 1967 Chev. truck engine in a salvage yard in Goffstown, NH, back in the 1980's. The one on the right is a NOS valve that was sold over the counter. Why do I need to take the "dark" valve to a plating company? I know it's an original. It really doesn't matter to me if it's black phosphate or black oxide, it's an original.

Dave