66 Big Block valve cover bolts

[Edward S.]

The new tech manual says 1966 BB valve covers have 7/16" head bolts, although I have seen and heard that 65 and 66 valve covers have 3/8" head 1/4-20 bolts with a recessed head. Noland Adams vol. #2 book on page 355 clearly shows a new L72 with 3/8" recessed head valve cover bolts. Their are also pictures of other 427's with 7/16" head bolts. I have been told that 65 and 66 should be 3/8" recessed heads and that the 7/16" head started in 1967. Does anyone know what is correct for each of these three years,65,66,and67? Thanks for any replys. Ed

[Michael H.]

Re: 66 Big Block valve cover bolts

Edward,

The 3/8" hex head valve cover screws were used on 65 and part of the 66 model year big blocks. I don't know exactly when the change to 7/16" occured but it was probably at some point around mid production.

[Anthony P.]

Re: 66 Big Block valve cover bolts

Mine was built 12/16/65, 390 HP has 3/8 recessed bolts. if that helps!

[Matt L.]

Re: 66 Big Block valve cover bolts

Edward,

The 3/8" hex head valve cover screws were used on 65 and part of the 66 model year big blocks. I don't know exactly when the change to 7/16" occured but it was probably at some point around mid production.

this is my 427 assembled on april 1,1966. i hope this helps.
take care,
matt
66 vette, misc 388.jpg