63 300hp Cam

[Carl S.]

My engine rebuilder thinks the cam must have been replaced along with the timing gears, it looks new. He recomends keeping it since it shows no wear at all. It may have been the last thing done to the engen befor the car was parked for 13 years. The question is, is this a correct or a replacment cam for a 63? It has the following numbers GM-28 6930 and a date code E31. There is also a dimond between one set of lobes. There is no other signs of the engine being worked on. All of the valves pistons and bearings look original.
Thanks Carl

[Duke W.]

Re: 63 300hp Cam

The "base engine cam" (283-220,230,245,250,275; 327-250/300)used in base and some optional engines from 1957 to 1966 was replaced for the 1967 model year, and the "ID number" is 6930, so you have the replacement. The part number for this "assembly" of camshaft and dowel pin is 3896929, and the finished camshaft part number - referred to as "ID no." in parts catalogs is 3896930, and either this entire number or the last four digits should be molded into the casting blank. This continued as the base engine cam through 1980.

The current replacement for this cam is 14088839. The basic timing numbers are the same, but there is a very slight change in dynamics, which can only be discerned via detailed inspection and analysis of the engineering lobe data.

The early cam used the same lobe on both sides with duration at .050" lifter rise of 196 degrees and points of maximum lift indexed at 109.5/112.5 and was designed for the medium port small valve heads circa 1957. The second design (ID 6930) has durations of 194/202 with POMLs of 108/116. The increased exhaust duration and earlier POML yields an earlier opening exhaust valve as the most significant timing change. This compensates for the relatively restrictive exhaust port of the large port heads as OE machined, so the design is more closely "tuned" to 461 and later big port heads.

More signficantly, the dynamics were softened, so it's easier on the valvetrain, and this cam or 14088839 is a proper replacement for the pre-'67 cam.

If it has no wear then it can be reinstalled.

Duke

[Joe L.]

Re: 63 300hp Cam

Duke-----

There was actually a cam "between" the 3896929 and the 14088839. It was the GM #14060651. That was the cam that replaced the 3896929. The 14088839 later replaced the 14060651 and continues to be available in SERVICE to this very day.