Has anyone decoded their 340 serial number?

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dibbons

dibbons

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There is a 14 or 15 digit/letter stamping on the front of the block below the driver's side cylinder head. Anyone figured out all the numbers/letters? I have a service manual that supposedly explains everything, but the service manual states one of the numbers/letters designates the model of the vehicle. That's a new one on me. Half of the stamping on my block is blurry, might have to send it to forensic department of the FBI to read it for me.
 
Is that the one that was around Sacramento area a few weeks ago.

Post up the numbers.
 
3 or 0 ?
M or N ?
340
0 ?
423820
?? Last one. two, or three unreadable

according to service manual:
First letter: Series which is model year
Second letter: Manufacturing plant
Next three: Displacement
Next one or two: Model
Next four: Build date
Last four: Engine sequence #
 
3M340R423820xx

4238 = March 5 1973

Pretty late build 73 mpdel year engine.

Look on the pan rail, pass side for a VIN
 
Well, the build date does not fit in anywhere, I need to take a second look, at least I know how to decipher it now, Thanks.

I still don't know if the one or two numbers/letters after the displacement for "model" were used in all cases or just on some engines (regular, premium, high performance, etc.)
 
crackedback probably has it figured out now, It's just that "R" sure looked like a "zero" or an "O". I think I read these things were actually hand stamped.
 
Why doesn't the build date fit? What's the casting date?

VIN fits with a 73 built engine. If you were thinking it was an earlier block, it's not a 71 engine.
 
Looks like 9 29 71 on the block. Flat top pistons have notches toward the front and a double set of valve reliefs, top of pistons (stamped .040) seem to be exactly even with the deck at TDC. Harmonic balancer has three or four holes drilled for balance and accepts a crankshaft pulley that only goes on one way.
 
Unlikely that the cast date is '71.

The VIN is a '73 and the serial number is a '73.

Though, it's a bit hard to see clearly from here.
 
The '1" in 71 looks a little weird, maybe it's supposed to be a "2" or "3". I will post a foto later for all to see.
 
Date of casting

DSC00008.JPG


DSC00002.JPG
 
Well, the block color would indicate 71....

'73 engine would be blue. Looks pretty clear that it's the original paint.
 
Doesn't mean it's not the original paint....but, it's odd that a '71 engine has a '73 serial number.

These numbers are normally a few months apart. Normally is not always, however.
 
It's not unheard of for unscrupulous persons to modify casting dates (though it would be odd on an engine with two other 1973 dates on it). You able to get a screwdriver in there and scratch around a little?
 
The rear cam plug has a bunch of silicon goop on it which I don't think is factory and it's painted orange. But it's hard to find any blue paint, if it was hot tanked before the rebuild, the old paint would have fallen off I guess.

Where should I scratch around, you mean around that supposed "71" number?
 
Yeah, but at a second glance it looks ok.

You able to get a pic of the block 3M340 number at the front under the left head? Did you figure those numbers out?
 
9/29/71 or even 8/29/71 would make it a 1972 model year engine at the earliest... what color were those supposed to be? Wasn't as though the big 3 had much of an idea regarding JIT inventory back then or rotating stock. Wouldn't be the first block to sit around a year + before being assembled.

Original paint? Yeah sure, that's it. LOL Not a chance with the casting date and model year designations.

The first 3 on the front of block could possibly be a "J"
 
1972-73 340's are normally blue.

crackedback, there are plenty of old small blocks around with their original paint...I've got one here in my '72 B body.
 
crackedback said:
9/29/71 or even 8/29/71 would make it a 1972 model year engine at the earliest... what color were those supposed to be? Wasn't as though the big 3 had much of an idea regarding JIT inventory back then or rotating stock. Wouldn't be the first block to sit around a year + before being assembled.

Original paint? Yeah sure, that's it. LOL Not a chance with the casting date and model year designations.

The first 3 on the front of block could possibly be a "J"
Click to expand...
Junes usually are, I have a June '71 1972 model 340 with external balance and 915 heads, my June '72 340 had 587s on it. 340s were relatively low prodution, and '73 I think it was they started exporting them- but an older block being used on a newer motor doesn't seem out of the realm of possibility.

2s and 3s were blue.
 
Mr Gorsky said:
1972-73 340's are normally blue.

crackedback, there are plenty of old small blocks around with their original paint...I've got one here in my '72 B body.
Click to expand...

If it had ORIGINAL paint what color should it be? It's not that hard to figure out. Which color would a 72 or 73 engine be?
 
crackedback said:
If it had ORIGINAL paint what color should it be? It's not that hard to figure out. Which color would a 72 or 73 engine be?
Click to expand...
The 318/360 light blue.

That looks like it was stripped of its paint and painted red.
 
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