carlisle61

When were 9 fin vs 7 fin valve covers used?
Thanks

ohiovet

9 fin valve covers were used in 1956 and early 1957.
I will check my NCRS Judging manual later today to get a changeover date.

DZAUTO

ALLLLLLLLLLLLLLLLLLLLL 2x4 56 engines and the optional 57 engines up through about Dec 56-Jan 57 had 9-fin covers. They were all "low script". The early (57-58) 7-fin covers were also low script. Then beginning sometime in 59, they were "high script". In LATE 59, the bolt pattern on the heads changed from a staggered to a straight across configuration. Subsequently, the valve cover bolt pattern also changed to straight across. In mid-66, the mold for the covers developed a crack right through the o in Corvette and as a result, ALLLLLLLLLLLL 66-later, as well as service replacement, covers have the crack. The crack is VERY noticeable. Some people, and some of the aftermarket vendors, have made efforts to buff away the crack----------IT STILL SHOWS!

Oh ya, VERY EARLY 57 FI engines had the full 9-fins. but it was quickly discovered that the top fin interfered with the air meter on the FI unit. So on the LEFT valve cover of FI engines, a notch was cut into the top fin for clearance of the air meter. It is commonly accepted that is why the covers were changed from 9- to 7-fins in mid-57.
The LAST year for Corvette script alum covers was 67. The optional 68 engines got chrome valve covers and beginning with the 69 models (and Z28 Camaro engines), the optional engines got a totally different finned alum cover WITHOUT the Corvette script.
Both Corvette script and 69-later alum covers were available for MANY years as service replacements from Chevy parts dept-----------------AND THEY WERE CHEAP (about $25ea)! Wish I'd bought a ton of them!

MikeM

In addition to the above, there was also a 69/later style aluminum valve cover released that had a push in rubber plug in the oil fill hole instead of a twist cap.

I don't know if it was reg. prod but it was serviced.

Todd H.

As Tom said, finned aluminum valve covers were for optional engines only. My NCRS 56-57 Judging Guide (fourth edition) says the switchover from 9 to 7 fins occurred in 1957 on dual 4 engines after VIN 3900. 3900-4500 were 7 or 9 fin, and all 7 fin after VIN 4500.

On FI engines, up to VIN 1900 had uncut 9 fins. 1900-2900 were 9 rib with the cut Tom mentioned on the top fin on the left cover (or both) to clear the air meter, and supposedly VINs after 2900 had 7 fins. These VINs are still somewhat approximate, though, since my original FI #2968 has 9 fins with the left one having the cut. I figure that makes it the last one, inflating it's value by 200%.