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Help for date code on BBC heads

19K views 12 replies 9 participants last post by  Vintage 68 
#1 ·
Hi, I am looking for some help with the date code on a set of heads I have. I have searched but have not found the exact answer I am looking for. The heads are a set of 3964291 closed chambered square port heads with a date code of L1, and this is where it gets cofusing, a small blob or what looks like maybe a symbol and either an 8 or could be a 0 if they put a line through the middle of the 0 like some do. If these are 1970 heads would there be a 70 or just a 0. If they are 68 heads could they be original to my late 68 camaro 396 car that I bought in 1982.
Sorry if I have duplicated this question but I could not find an answer during my search.

thanks
 

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#6 ·
Re: help for date code on bbc heads

If they were 1970 there would be 70. I would say either L 1 8 or L 1 9
Nov. 68 or Nov. 69. I think they remove I from calender dating , so 11th month 109 cc heads.
Don't think so. On 70 cast heads, it would read L 1 0. However, that is either L 1 8 or L 1 9, as GM did not put a line through the 0. Sometimes very hard to distiguish 8 from 9 on those casting dates.

Here is a 186 head cast Feb 4, 1970 (B 4 0)
 

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#3 ·
Re: help for date code on bbc heads



Are both heads the same date?

L casting date month is December. See this link.
http://www.camaros.org/numbers.shtml#GM-InternalDateCodes

The 291 heads were not used on 1968 vehicles. If the date code on yours is December 68 - they would have been on a 1969 model year vehicle. If December 69, then on a 1970 model year vehicle.
 
#5 ·
Re: help for date code on bbc heads

I agree that the 3964291 heads were from the 70 model year, great pair of heads.
 
#8 ·
Thanks to everyone for the replys the info was very helpfull especially for the info regarding the month of casting. I have taken a better look at the second head and it has a little better year cast into it with the same month and day. L 1 :) 8
Now that I have a better idea about what these heads are and when they were made I will be able to decide if I will reinstall these back on the 427 in the car or find a more suitible head for my combination.

Thanks again

mike
 
#9 · (Edited)
Those heads were used 69 and 70. One thing you guys missed is the spark plug hole size. ALL 1970 model year heads used the small tapered seat spark plug and all 69 models used the larger flat washer type speark plug. the spark plug hole will tell you which year they are.


The pic looks like L 1 1969 to me, check spark plug holes for tapered seat machining
 
#10 ·
... ALL 1970 model year heads used the small tapered seat spark plug and all 69 models used the larger flat washer type speark plug. the spark plug hole will tell you which year they are.
^^^ :thumbsup:

Looks like Dec. 1 1969 to me :yes:
Cast on second shift ...
 
#11 ·
The date would be L 1 9.
The 840 casting heads were phased from casting production in May of 1969.
The 291 casting heads did not begin production unitl June of 1969.
The first production runs of 291 heads have washered plugs.
Late 69 engines, from July to October, have been found with mixed casting heads one #840 and one #291.
Hope this helps.
 
#12 ·
Wow, My first post and I have already made a mistake. Really thought that 9 looked like an 8 but after looking at it closer and comparing it to the 9 in the 3964291 it must be. Also the heads do have the tapered plugs.

Thanks again.

Also one other question, just out of curiosity how do you know they were cast on the second shift? Is it the GM2T
 
#13 ·
:noway:
The shift is indicated by the shape of the screw(s) used to anchor the casting date plate ;)
(or on the 'clock' used on some other parts)
Most GM casting plants operated in two 10-hour shifts.
'Flat' is 1st shift
'Round' is 2nd
 
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