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post #1 of 21 (permalink) Old 08-17-2015, 03:53 PM Thread Starter
 
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engine numbers

My 67 gto has a date stamp on the motor as "K146" and a block casting code of 481988. It looks like these two numbers can't be on the same motor. Can anyone explain this? Thanks.
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post #2 of 21 (permalink) Old 08-17-2015, 04:33 PM
 
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the gm block casting # 481988 was used on 400 engines from '67 -'78. you gotta have the the 2 letter code up front n casting date to ID a Pontiac engine.
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post #3 of 21 (permalink) Old 08-17-2015, 05:09 PM
 
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Originally Posted by rickm View Post
the gm block casting # 481988 was used on 400 engines from '67 -'78. you gotta have the the 2 letter code up front n casting date to ID a Pontiac engine.
That's a stretch, the 481988 casting 400 block was first cast in early July of '70, for '71 model use. the 481988 casting 400 block was cast for use into the early into the '75 model year, then its use was discontinued, replaced by 500557 400 (thin main webbing) block.

For the '78 model W72 400 blocks, code X7 and WC, the 481988 casting block again began being cast in the late summer of '77. This time it had an XX casting in the valley area, and only 3 bolt bosses tapped for clamshell enginge mounts brackets. The casting of the W72 blocks continued for several months up into April of '78. The Pwh coded 400 4spd blocks for '79 400 4spd T/A's and Formulas also used the Late casting version of the 481988 blocks. Every Pwh block I've owned has been cast in late Sept or Oct of '77, which jives with them being stockpiled for '79 usage.
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post #4 of 21 (permalink) Old 08-17-2015, 05:38 PM
 
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Originally Posted by Pinion head View Post
That's a stretch, the 481988 casting 400 block was first cast in early July of '70, for '71 model use. the 481988 casting 400 block was cast for use into the early into the '75 model year, then its use was discontinued, replaced by 500557 400 (thin main webbing) block.

For the '78 model W72 400 blocks, code X7 and WC, the 481988 casting block again began being cast in the late summer of '77. This time it had an XX casting in the valley area, and only 3 bolt bosses tapped for clamshell enginge mounts brackets. The casting of the W72 blocks continued for several months up into April of '78. The Pwh coded 400 4spd blocks for '79 400 4spd T/A's and Formulas also used the Late casting version of the 481988 blocks. Every Pwh block I've owned has been cast in late Sept or Oct of '77, which jives with them being stockpiled for '79 usage.
that's what my cylinder head/block ID guide says. AUTOMOTIVE ENGINE REBUILDERS ASSOCIATION. COPYWRITE AERA 1981. I worked at a auto parts store / machine shop in the mid. '70s. this book was our bible for identifying heads n blocks for ANY American engine, not just Pontiac. I looked in another old book I have n it says not till '71 like you said.

Last edited by rickm; 08-17-2015 at 06:18 PM.
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post #5 of 21 (permalink) Old 08-17-2015, 06:30 PM Thread Starter
 
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Thanks, but I still don't see how it makes sense in light of the date stamp. Do you?
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post #6 of 21 (permalink) Old 08-17-2015, 06:46 PM
 
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Thanks, but I still don't see how it makes sense in light of the date stamp. Do you?
Look at the last number of the date code REAL close, to see if it could actually be a 0 thru 5, instead of a 6.
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post #7 of 21 (permalink) Old 08-17-2015, 07:10 PM Thread Starter
 
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It's perfectly clear. I have a good photo of it. I wondered if it could be 1976 instead of 1966, but that don't make any sense either.
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post #8 of 21 (permalink) Old 08-17-2015, 09:25 PM Thread Starter
 
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can you make sense out of my date stamp?
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post #9 of 21 (permalink) Old 08-17-2015, 10:24 PM
 
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Originally Posted by Mike Oshinski View Post
can you make sense out of my date stamp?
As mentioned, all 400 blocks used in '76 and and '77 were 557 blocks, including the '77 W72 engines. So, I can't see any 481988 blocks being cast in '76. Then, as mentioned, the '78 & '79 W72 engines used the XX481988 blocks, with only 3 motor mount bolt holes. All the date codes on these blocks, which I've seen are from '77. I've read that no Pontiac 400 blocks were cast after '77. Can not confirm. But I've never read of anybody who has seen a 400 with a '78 date code.

If all this is true, then the only thing that remains is that whoever set the date code numbers which were cast into your block just simply used the wrong last number--a simple mistake. There were a lot of those on the auto assembly lines. I've read about all sorts of stuff that did not come off the assembly line as it was supposed to. Hey, people are human and make mistakes.

By the way, what is the 2 digit code, off the front of the block ?
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post #10 of 21 (permalink) Old 08-17-2015, 10:34 PM
 
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Mike, the following are "5 bolt" engine mtg bracket 400 blocks, first introduced lfor the '70 model. earlier 400 blocks had their own casting number AND only had provisions for two bolt engine mounts.

#979914 '70 model 400, both 2 bolt and 4bolt main caps (4 bolt is typically RAIII,mthough a few '70 WT 400's have surfaced w factory 4 bolt caps

#979915 or 97991(5) '70 RAIV, but a few '70 WS RAIII also used his casting
*the last digit, 4, was wiped and the proper font large 5 was stamped.

#481988. First cast for '71 400 usage but continued on into early '75 model production. The complete application of the 481888 block is exactly as I mentioned above. Throughmy specialty core business I provided select 400 shortblock cores along with 6X-4 head cores for many years to a major national Pontiac engine builder. I seriously doubt anyone on his forum has had as many 400 Pontiac cores go through his hands.

#500557 Partial '75 usage, then into '76 model.
During the'76 model year, the 5 bolt mtg boss arrangement on side of the block stopped and the late style 3 mounting boss block began. Crank register size (for the flywheel) changed from 2.75" to 2.5" as well.


Checked my engine code/ build database, the following is the earliast 481988 casting 400 have run across. Note block cast July 1st, 1970.

(004541......YS........G010.......08D.....276571A1 00529....400 Grand Prix (Paul's farmer yard)

The above pertinent info is from an extremely early '71 build from the Lakewood GA plant.
The VINs of T-37's, LeMans, GTO's, as well GrandPrixs all were intermixed at the plant as far as the sequential last 6 digits go, the preceding and following VIN could be another GP or a Pontiac A-body.
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