66 L72 BB on e-bay

[P.J. McGrath]

I have seen a number of rebuilt short blocks for sale lately on e-bay advertised as 66 L72 427/425 HP motors with casting number 3855961. All my Vette literature states that the 66 L72 block is casting number 3969942. When I do a general web search of 3855961 several sites list both casting numbers as having 1966 Corvette applications. Does anyone know the history of this block and why there is confusion as to its application?........P.J.

[Jack H.]

Re: 66 L72 BB on e-bay

Noland Adams says:

"The L36 engine cast and assembled in Tonawanda, New York. The block's casting number was 3855961 on early production engines, but most were built with the casting number 3869942."

The Corvette Black Book recognizes either casting as 'correct' for '66 BB Corvettes.

But, the NCRS Judging Guide for 1966 only recognizes the 3869942 casting for BB Corvettes with an early vs. late distinction dealing with the presense of reinforcing 'gussets' cast into the front of the block up to approximately VIN 1700 just above the timing chain cover.

Those selling the 3855961 blocks may be using sources other than NCRS as their confirming authority for the block's being 'correct' for '66 Corvette....

[P.J. McGrath]

Re: 66 L72 BB on e-bay

I dusted off the cover of Mr. Adams' book and there it is on p. 379. I wonder why the other sources don't mention the early block?.........P.J.

[P.J. McGrath]

Re: 66 L72 BB on e-bay

I pose another question. Mr. Adam's book suggests that the 3855961 block was used as late as Ocober 1965. Surely someone with one of these blocks has had their car judged. Has anyone seen this and what was the outcome?......P.J.