1968 Tri-Power PCV Part Number?

[William H.]

The 1968 Judging manual says all cars were equiped with PCV CV736C and that they were on the driver's side valve cover. Am I misreading the manual or is it just incorrect? Is it valve 746c or 736c? It also says the hose uses a 1 1/2" tower clamp. Is that correct? Thanks if anyone can clarify.

[Terry M.]

Re: 1968 Tri-Power PCV Part Number?

Something has to be bad wrong there. Even Ray Charles would know that a 1 1/2-inch clamp of any type will not fit on the PCV hose. There were no tower type clamps on the PCV hose. Do you have a Edition and page number to cite please?

[William H.]

Re: 1968 Tri-Power PCV Part Number?

1968-9 Tech Info and Judging Guide Third Edition. Page 61. The tower clamp I maybe misread and it's used on the 'air inlet' and not the PCV so that makes sense. It still has some misleading information on location and part numbers. Thanks for taking a look.

[Terry M.]

Re: 1968 Tri-Power PCV Part Number?

Ah Ha. The 1.5 inch refers to the air inlet on Mark IV motors (big blocks). Small block air inlets have no clamps on them, they are force fit. There is a dark green -- almost black spring clamp on the hose at the PCV valve, and on there is the same clamp on the carburetor end of that hose. Some might say those clamps are black, but I think they started life dark green and turned black. I am sure we could argue or discuss that point for some time and not reach a conclusion. Those clamps will have three "ears" that have square ends. More recent, so called safety clamps have rounded ears that are less likely to cut a person.

As to the PCV valve numbers: There has been some past discussion on this board regarding that. I strongly doubt there was just one number for ALL engines offered in 1968-69, and I am sure the numbers have been posted on here. They might also be in your Owner's Manual (Specifications section). I would not base my purchase on what is in the third edition 1968-69 TIM&JG.

[David L.]

Re: 1968 Tri-Power PCV Part Number?

The 1966 & 1967 Corvette AIM's list # 6423438 as the part number for the PCV valve for the L72, L36 and L71 engines.
According to my research: AIM # 6423438 = GM # 6421981 = CV-691C
The "late" 1967 427 models may have been issued the "machined steel" (very early version) CV-736C PCV valve even though there is no documentation in the AIM.

The 1968 Corvette AIM lists GM # 6424251 as the part number for the PCV valve for all engines. GM # 6424251 is also listed as the PCV valve in the 1968 Camaro and 1968 Chevelle AIM's for the base V8 and L78 engines.

The 1969 Corvette AIM lists GM # 6484541 as the part number for the base, L71, and L36 engines. GM # 6484541 is also listed as the PCV valve in the 1969 Camaro AIM with base V8, L35, and L78 engines and in the 1970 Camaro AIM with all V8 engines.

Based on my research I believe the following:
AIM # 6421271 = CV-691 = GM # 6421545 (used on 1965 Chevrolet 396), I found a "CV691" ("machined steel") valve on a 1965 Chev. Convertible (396) back in the early 1980's in a salvage yard.
AIM 6423438 = CV-691C = GM # 6421981 (used on 1966 Corvette L72, 1967 Corvette L36,L71, and 1967 Camaro L78)
AIM # 6424251 = CV-736C (early version, stamped steel) = GM # 6423695
AIM # 6484541 = CV-736C (later version, stamped steel) = GM # 6423695

From Chev. Parts History (over the counter parts): GM # 6421545 was replaced in May 1965 with GM # 6421981 which was replaced in July 1969 with GM # 6423695.

In the photo with the 3 PCV valves I believe that the one on the left is AIM # 6424251, the early version "stamped steel" CV-736C.
The middle valve is from a 1969 which appears to be identical for 1969-1972 models.
The one on the right is NOS from a 1984 dated box.

Also, based on my research I believe the following:
1968 Z28: AIM # 6483766 = CV746C (early version) = GM # 6484625
1969 Corvette L88 and 1969 Z28: AIM # 6484699 = CV746C (later version) = GM # 6484525

From 1969 Z28 AIM: AIM # 6483766 replaced 10/30/68 by AIM # 6484699

From Chev. Parts History: GM # 6484625 replaced in Jan. 1968 with GM # 6484525

I would appreciate any comments on my research,

Dave

[David L.]

Re: 1968 Tri-Power PCV Part Number?

Enclosed is a photo of an original "late" 1967 Corvette w/427 CV736C PCV valve ("machined steel", very early version) courtesy of a fellow NCRS member. My guess is that this type of CV736C valve was also used on "early" 1968 Corvettes.

Dave

[William H.]

Re: 1968 Tri-Power PCV Part Number?

Great info, Dave. Really appreciate your research.

[Ronald L.]

Re: 1968 Tri-Power PCV Part Number?

Dave, the pic in the post above is a very likely a 1966 manufactured valve. Remember, those went on the L72 427's starting around the beginning of 1966.

At some time in late 66 to 1967 the text on the 691 and 736 valves changed and is identical to that seen on the hybrid valves dated 1968, namely solid metal top, thin metal formed bottom.