Some months ago, there was a minor discussion on the board relative to the AC CV-736C Positive Crankcase Ventilation (PCV) valves. As I recall, the subject came up in the course of some other thread. Anyway, I mentioned that I would post some information later regarding configuration differences in these valves and, now that I have a moment, this seems like a good time.
As many of you know, the AC CV-736C PCV valve had rather wide usage in Corvettes during the 1967-1972 time period. It was used on many 1967 427-435 engines and also most 68-72 engines with the exception, primarily, of 70-72 LT-1 and 1969 L-88/ZL-1 engines. The configuration of all original CV-736C valves was the same and, for a considerable period of time thereafter, service replacements were also identical to the originals. However, the configuration did change somewhat over the years since. Understand, though, all valves, even to the present day service replacements, are basically the same general configuration, with small detail differences. Herewith, a synopsis of the different configuration detail changes:
1967-1981
During these years of production of the valve, the cylindrical section of the valve(which inserts into the valve cover rubber grommet) has the stamped inscription "AC SPARK PLUG" AND "CV-736C". Around the very bottom of the cylindrical section are four, approximately equally spaced manufacturing marks which appear as indented "dots". Looking at the valve from the bottom through the hole in the case, the bottom of the internal valve has the raised letter "D".
1982-1988
During approximately this time period's production of SERVICE valves, the configuration changed slightly. The cylindrical section still read "AC Spark Plug", but there were, variously, 4 or 9 dot-like manufacturing marks around the base. The internal valve's "D" raised letter was replaced by an "M".
1988-1997
During approximately this time period's production of SERVICE valves, the configuration once again changed slightly. The "AC SPARK PLUG" inscription disappeared and was replaced by "AC ROCHESTER". All valves had the 9 dot-like marks around the base and the internal valve raised letter designator was "M".
1998+
SERVICE valves manufactured after about 1997 are identical to the above in configuration, EXCEPT that they have an olive-drab coating over the valves apparently zinc plating.
As many of you know, the AC CV-736C PCV valve had rather wide usage in Corvettes during the 1967-1972 time period. It was used on many 1967 427-435 engines and also most 68-72 engines with the exception, primarily, of 70-72 LT-1 and 1969 L-88/ZL-1 engines. The configuration of all original CV-736C valves was the same and, for a considerable period of time thereafter, service replacements were also identical to the originals. However, the configuration did change somewhat over the years since. Understand, though, all valves, even to the present day service replacements, are basically the same general configuration, with small detail differences. Herewith, a synopsis of the different configuration detail changes:
1967-1981
During these years of production of the valve, the cylindrical section of the valve(which inserts into the valve cover rubber grommet) has the stamped inscription "AC SPARK PLUG" AND "CV-736C". Around the very bottom of the cylindrical section are four, approximately equally spaced manufacturing marks which appear as indented "dots". Looking at the valve from the bottom through the hole in the case, the bottom of the internal valve has the raised letter "D".
1982-1988
During approximately this time period's production of SERVICE valves, the configuration changed slightly. The cylindrical section still read "AC Spark Plug", but there were, variously, 4 or 9 dot-like manufacturing marks around the base. The internal valve's "D" raised letter was replaced by an "M".
1988-1997
During approximately this time period's production of SERVICE valves, the configuration once again changed slightly. The "AC SPARK PLUG" inscription disappeared and was replaced by "AC ROCHESTER". All valves had the 9 dot-like marks around the base and the internal valve raised letter designator was "M".
1998+
SERVICE valves manufactured after about 1997 are identical to the above in configuration, EXCEPT that they have an olive-drab coating over the valves apparently zinc plating.