<VV> Engine block codes

[corsa]

First I am not familiar with how Chevrolet codes for Bodytag dates on
Corvettes.
If what you have stated about Corvette numbering is true, then Corvairs use a
different coding for body build date than Corvettes. The decoding of fourth
week of April is correct, just like it states in Bob Helt's book.. Corvair
Bodies are produced by Fisher. Corvette bodies are produced by Chevrolet.
Craig, take a look at your Corvette bodytag. It will say "Body by Chevrolet".
Corvairs on the other hand say "Body by Fisher". Since Fisher is totally
separate company from Chevrolet, the body build date will always precede
actual production date. Fisher may hold a body anywhere from a day to several
weeks before delivering them to Chevrolet. Usually Fisher delivered the
Corvair bodies in a timely manner and they did not sit in the "Body bank" for
long, but this was not always the case. It is known that some 1969 bodies sat
for months in the body bank before delivery to Chevrolet. The engine and
components will be added to the body after delivery from Fisher and a Vin will
be attached at that time. Engine blocks also have to be delivered from
Tonawanda, so body build date, engine block date and actual production date
will usually be different from each other. I have found through the 1965
bodytag survey and the 66 Turbo vert registry that most Corvairs have a engine
block code dated approximately a week prior to bodytag date. (70% +) But some
Block codes are a week or two after the Bodytag date. This can be explained by
Fishers "banking" the body until needed by Chevrolet. So for Andy, a engine
dated approximately a week before Bodytag date would be ideal but a week or
two preceding or after the bodytag date would be OK.  Of course all bets would
be off for 1969 cars if the Vin wasn't stamped on the engine. My car has a 4D
(April 4th week) bodytag date, a T1205AF Engine code (Dec 12th) with matching
Vin, and a May 14th Production date.

Cheers
Bigwave Dave

---------------Snip-------------------
My body Tag says 04D so I'm guessing I need T0421YR to T0507YR to be  in
 the correct date range. But I could be wrong I'm still not completely clear
on
 the block code to body tag code relationship. <unsnip>

The block number always precedes the body assembly date so 507 is too late.
I don't know about Corvairs, but in Corvettes the engine date is between -2
days and about -5-6 weeks from body assembly date.  The engine cannot be made
after it's put in the car  While Bob Helt's authoritative book decodes 04D as
"forth week of April", 04D decodes to the fourth of November if Corvair dates
are decoded like Corvettes.  In Corvettes, the body is one exception to the
numbering scheme.  In 99% of the other date codes, A=January and L or M is
December (some makers skip "I" (letter I looks too much like number 1).
Components
follow this scheme EXCEPT for the body build where A= August!  (B=Sept,C=Oct,
D=Nov).  IF Corvairs follow this thinking, you would want a block code up to
TO1102 back to around TO1002 (two days before body assy to a month before body
build.

I suggest that you research this fully and confirm the decoding of the body
tag with a second or third authority before you select a block date.  I don't
know why GM would use different body date schemes between lines and I am
positive about the Corvette scheme.