Here is another very interesting post taken from the CP site.
Mr. Ransom, you da man.
Topic: 60949
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- Engine numbers 70 T/A - Tom Tabor Bio 6/10/05 9:01
Just wondering what all of the different numbers on the block are for.I know the one close to the timming cover is the number that matches my vin# then above that near the pass head is another series of numbers plus YZ. At the back is a 70 then another number near the pass head. Anybody have a book that tells about these?
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John V. Bio 6/10/05 10:01
Lots of resources to find decodes for engine nos., some good, some not so good, none perfect.
The 7 digit code by the YZ is the Motor Unit No. It will start with a 0 because Pontiac never assembled 1,000,000 units.
The M.U.N. is an engine assembly serial no., if your no. is 0123456, it just means this was the 123,456th engine assembly put together at the Engine Plant (Pontiac only had one engine assembly plant, located at the home facility in Pontiac, Mich from where they were distributed to the various Final Assembly plants based on production demand) for the '70 model year.
The YZ is a manifest code. The Build Order would call for components by manifest code, the engine assembly was no different. When the Build Order called for a YZ code engine assembly, they pulled one out of inventory and put it in the car. The Engine Plant had a recipe that told them what each engine assembly should consist of by manifest code. If they didn't screw it up, the YZ would call for specific block, cam, heads, crank, intake, distributor, exhaust manifolds, etc. The carb was added on the final line (also by manifest code) and was not part of the engine assembly.
The number at the rear of the block on a ledge behind the no. 8 cyl is the block casting p/n. Should be 9799914 for a '70 400 block. This was the p/n assigned to a casting that the foundry produced. The p/n was assigned by Pontiac Engineering just like any other p/n assignment as they designed and released the parts. Pontiac did not service bare blocks so you will not find this p/n listed in the Master Parts Catalog.
On the pad by the Distributor hole you will find the cast date code. This code will tell you when the block was cast. It does not indicate when the engine was assembled, although obviously it was assembled AFTER the block was cast and BEFORE the car was built.
The Motor Unit Nos. can be carefully studied for a given model year and a fairly close approximation/guesstimation of the date the engine was assembled can be made.
For matching nos., a careful study of the p/n's, cast or assembly dates, and any other markings of ALL of the individual engine components can be done to determine if everything related to the motor is factory correct and apparently original.
Ask here if you have a specific question. Nice part about this forum, if you get bad input, somebody else will be sure to jump in and correct it. Read a book and you might take as gospel something that others have proven wrong.
Tom Tabor Bio 6/10/05 11:58
John, Thanks much for the info, very interesting. The number on the back is 9799914 and by the distributor hole it has a 70 and under that 0120. To the right must be the day or night as the arrow is pointed to the D with a 4 under it. The front number above the YZ is 0461577. On the build date number would the 0120 be Jan 12, 1970?
John V. Bio 6/10/05 12:37
You're misreading the cast date code, which is common and why I never like to use that code for engine decoding.
The '70 'bird went on sale early Feb, '70. I believe the earliest cars were being assembled mid Jan and obviously, 'bird engines were assembled and at the Final Plant by then.
But I suspect what you see as 0120 is either C120 or D120 (March 12 and April 12, '70 respectively. More often I suspect the C will be read as an O or 0, but could be a D I suppose. Either way, the iron foundry cast date codes will always be a letter followed by 3 digits in 1970. Check the Time Built code on the Body Data Plate. That code will read something like 03E or 05A meaning 5th week March or 1st week May. That might help determine what the block cast date is most likely.
You are correct about the Day Night shift pointer.
I do not have a Motor Unit No. log for 1970 motors, but 0461577 is most likely a motor assembled in March or even later from evidence of other model years.
Tom Tabor Bio 6/10/05 14:08
John, Again thanks for the great information, I will double check that date code tonight, it must be a C as I believe that according to the PHS info I have the car was built the end of March.
Kings Ransom Bio 6/10/05 20:18
According to the M.U.N., your engine should have been cast in March.
Tom Tabor Bio 6/10/05 21:59
I re-checked the date and it was C120, March 12, 1970?
transamric Bio 6/11/05 2:40
Yep.
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