Julian Date Codes


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As many of you know the Julian date code system was employed to date the day of manufacture beginning with the "814" 1963 "W" block. Prior to that Chevy used the more conventional system showing the month and year of casting. I've just done a great deal of research on this to get information about my car and I want to share this on the forum so nobody else has to go through what I just did.
My greatest problem came from not recognizing the actual date code on my engine because it was only two[2] digits. Every proper explanation of the Julian Date Coding system I found calls for a three digit code in all cases. Thus, an engine casting on say February 15 would properly be coded 047 allowing 31 days for January and 15 more for that date in February. HOWEVER, that's not the way the boys at the foundary actually did it!
In the case of my engine it was coded "23" and that translates to January 23. I see no problem with them doing that but my job sure would have been a lot easier if I knew they did not use zeros in front of the numbers. I'm guessing now, but I suppose a single digit number is also possible here to account for those casting dates between January 1st and January 10th, 1963.
I need to give credit here to that OLDSKYDOG - Cecil who posed the following in a different thread>>>oldskydog Dec 12, 2009
"Just a minor technicality, but julian date codes were not always 3 digits. Zeros were not placed in front so the first three digit date code would be 100. January 1 would be julian date code 1."
If I would have seen Cecil's words earlier it would have saved me a lot of work.
Retrieving the casting date code off an engine that is still in the car is no picnic. My little wife Patty spent a lot of time actually laying across the fender and on top of my 409 engine padded with towels trying to do this. Until we discovered our best method she got the number by using a mirror and her digital camera. I want to caution anyone doing this to be careful when translating the mirror image but also to be even more careful about cleaning the casting numbers with a small wire brush. As we cleaned it up our actual number "23" was first a 28 and then a 29 as the dirt was progressively cleaned out of that tricky #3 cast number.
Regarding the best method to find/see these numbers, ours turned out to be a camera and tiny 6 inch TV system we had for underwater inspection work. This is something you can buy for about $60 at Harbor Freight but its a black and white only model. They also have a color model for about a hundred bucks. I think any decent security camera hooked up to a TV would work just as well. Of course you can also purchase a special remote inspection device and any of these alternatives should be just fine... they beat having to pull the engine, that's for sure!

All the best,
BuzGuy at Harveys Lake, PA.
PS: I am doing this as part of an attempt to get my car documented for the National Impala Association through Jersey Late Greats, Inc. Tommy Nolan hooked me up with them and they sure do appear to know what they are doing.
PPS: Julian Date Coding is not used all the time


Well Known Member
Supporting Member 9
Thanks for the hat tip.
Actually the julian date coding began in 62, as I recall, sometime in June with the o68 blocks and coincided with the CFD as the foundry mark, X on the front of the block and the use of Armasteel main caps.


Active Member
You were a little bit too fast for me Cecil... I wanted to post this picture of my dolly doing her thing for me. How many of you guys have a wife that would do this for you? This is a retired school teacher who never held a wrench in her life!!!
Bravo Patty,



Active Member
Yeah Cecil, I know damn-darn well she's a keeper... been keeping company with her since 1974 now and its been a great life. Listen, I'm not sure about that remark you made regarding the date of use for Julian date codes. I found this great resource for locating the exact place to look for these codes on allthese 58-65 "W" block engines and here it is>>> http://www.348-409.com/blockcast.html If you put your cursor over the year 58-62 it shows where the date code can be found. HOWEVER, if you double click on the date, then you get a new box that had another addressable lead. If you click on that and page down, there is actually a nice table of Julian numbers representng both leap year and non-leap year casting dates. One thing though... somewhere among all this data the say that Julian date coding was "Occasionally" used prior to 1963. Furthermore, if they made these 814 block castings in 1962 and they surely did for early 1963 cars, then that makes you correct kind of by default I guess. Look Cecil, I don't know who you are and you could be the foundry foreman for all I know. But, one thing I do know is what I know. Rather than just saying "squat", allow me the dignity to just say I am not ashamed to admit I am learning here... learning a lot.
Now, on a slightly different topic, one thing I've never seen posted anywhere has to do with that letter "X" casting mark you mentioned in your first post. I thought it was interesting if not darn important for anyone wanting to "work" a W-Block engine so I'm gonna post it here and now>>> I am given to understand that the casting mark X means that a much higher grade of carbon steel was used in casting these "X" blocks and that was done with the 814 blocks in preparation for the Z-11 project. How is that for a bit of Heavy Chevy Trivia? I must say my source for this is a knowlegable fellow I admire a lot... He never-ever uses computers.
All the best to All,


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Supporting Member 13
My wife of 37 years would also have no problem hanging off an engine like that. We both have very special ladies. My wife was the 1st girl to take Auto Mechanics at Martin Van Buren high in I think Queens, N.Y. She and I drag raced together for a lot of years. Grandma and Granpa racing at Westhampton Drags 1980.jpg


Well Known Member
Supporting Member 9
Congratulations. I too have been married to the same woman since 74.:cheers

Here is an example of an 068 block with a julian date of 266 which translates to Sept 23 which has to be 1962. The transition to the 814 block happened sometime in late Sept. 62. The first 068 blocks with julian dates, CFD, X, and Armasteel main caps appeared sometime in June, 62. Here is another example with a julian date of 166 (15 June, 62.

From one of my previous posts :

"I think I may have stumbled onto the changeover date from 068 castings to 814 castings as well as the changeover to the CFD foundry markings.:eek:
In researching some info for someone else regarding the appearance of the casting clock on 870 327 blocks for the 63 model year, I checked my records and noticed that my 63 814 CFD block has a cast date of 271 which should translate to September 28, 1962. I also have pics of an 068 block with a julian date and a CFD casting. It has a julian casting date of 266, which would be Sept 23, 1962. It also appears to have the X on the front as I believe coincided with the shift to the CFD foundry. Both blocks have the casting clock. I don't think I've seen a casting clock on any Tonawanda foundry blocks...somebody correct me if I'm wrong. It appears that the changeover occurred sometime between Julian date 266 and 271 in Sept 62.

As far as the use of the X on castings, there are many examples of that on just about every kind of casting throughout the years. Without actual documentation such as a foundry directive as to what the actual intent of the X symbol, we are left to examine the evidence of the examples and draw whatever logical conclusions make sense.
In general, the X cast symbol seems to have been used when a casting change had been made in order to track the item for any machining or service problems. You will find "X"s on various castings including most commonly some early 58 3x2 intakes, late 57 type 283 heads(539 castings) for 58 application with the X58 cast on them. Also the 58 283 blocks were cast with the X on them. The 58 283 block was changed from 57 by adding side mounting bosses. That might have been the reason for the X to indicate a pattern change.
Don't know about high carbon steel, may be true as Chevy started experimenting with malleable and nodular iron castings in mid-62 and ended up with a didicated nodular iron casting foundry in 67.
I have heard the "high nickle" explanation before, but without any documentation, I consider it a myth. There were changes made to the metallurgy in castings, but as far as I have been able to determine, there was no special marking on the piece to indicatge what the mix was.
Reminds me of the myth of the 010/020 markings on the front of a 350 block supposedly indicating the "high nickle" content making it a more desirable block. I don't know how that got started, by most likely someone was asked what the numbers mean and rather than admit not knowing, responded that it meant that it was a "high nickle " block.
In reality, those are the last 3 digits of the casting numbers of the various blocks that used that same front and rear pattern. I can probably tell you what numbers are under the timing chain cover by looking at the casting number on the block. You see the same thing on our W blocks.
Here is a discussion of the block casting process written by a guy who actually worked at the Saginaw foundry. The process would be similar at the Tonawanda (CFD) Foundry.

In response to a question about the "010/020 high nickle content block" myth from a thread on block castings on NastyZ28.com:

I work at a GM foundry. We make engine blocks, heads & cranks.

The numbers you are talking about (010, 020) are only sand core identification numbers. The 010 is a side core for a small block chevy, and it does not guarantee that the block is a 4 bolt or not. Most were 4 bolt blocks, but some 2 bolts were built with 010 side cores, or whatever side core was available. The 010 designation has nothing to do with metallurgy (nickel content)
Each time we make a batch of iron, a 10 ton crane will move across the metal staging area and pick up certain metals and dump them into the cupola. Each batch is done this way, and the irom metalurgy between each batch can differ slightly. Certain iron batches are made for certain parts and heated to certain degrees. The only true way to tell the nickel content is by part number. But that alone is only a guideline, and cannot be relied on 100%. Most high nickel blocks will also have a brighter sheen after a chemical cleaning. It would be the same sheen if a standard block was shotblasted 2-3 times.

Iron properties will differ from each run. Some will be harder due to longer mold line time, and some are slightly harder due to a multi travel through the shot peening booth.

But don't be fooled that harder iron is better. GreyIron (blocks, heads) under a microscope look like a slivered chip, whereas nodular iron (cranks, carriers) look like perfectly round balls. Grey iron that is hard will easily crack. Grey iron that is soft will easily wear. Nickel blocks are nice to have, but they will also be subject to mold line time. In the end, it'just a brag to a select few if you have a nickel block.

You need to understand how sand cores are created & assembled to have an idea of what I am talking about. The timing cover front slab core is a different sand core than the side slab cores or the rear slab core.

Each sand core has an identification number, so we can trace it back to the core number if there is a problem with the finished product. Because once the block has been poured, and mold line time has expired, the entire block mold goes through a shakeout process where the sand mold is destroyed and the iron block is extracted. Once this happens, all of the sand cores have been destroyed, and the numbers on each facet of the block is all we have left to trace identification.

Other identification areas are just inside the waterpump holes. You will see water jacket numbers there. You will also see numbers on the underside of the block, next to the first cam journal. This is the barrel core number. The large single digit number near the part number is the drag core pttern number. Alongside that, you might see CFD or GM-D, which means "central foundry Defiance, or GM-Defiance. SMCO means Saginaw metal casting operations.

Every facet of a block or head will have identification marks to tell me what particular core was used to create that particular part.

And as in your case, some cores are universal. Even all the big blocks & small blocks we make today use similar iron recipes. Some may have hotter iron batches such as the 3.8 cylinder head, but the ingredients are the same.... unless it's a bowtie run.

When we pour iron, the only reference to what we are making is the last 3 digits of the part number. "We're making 781's today!" We never refer to any other identification such as core numbers. The iron blend is purely based on the casting part number.

Think about going out to buy a GM block. Try and ask the parts guy that you want a part number "xxx", BUT with a 010 side core or a 020 front core. He will look at you strangely, and then laugh at you, because the differences are indexed by part numbers only, not by core numbers. His parts book is indexed by part numbers only as well. GM indexes all the differences with their parts by different part numbers.

Once all the cores are screwed together to make a core package, the package assemblies can sit on shelves for days before they are placed in the mold for an iron pour. And... once all the core pieces are screwed together to make a core package, there is no possible way for us to see inside to verify what core numbers were used to make the core package.... Because of this, we cannot follow the myth that 010 ID's mean "high nickel", because it's impossible to view the 010 ID once the package is screwed together & shelved. The only ID we have is the part number.

What you wrote was how it was supposed to be. But once it was put through the system, engineering realized that their intent could not be efficiently tracked. So the plan was abandoned, but it would have been too costly to rework all the patterns in the core machines, so those were left alone.

When engineering originally developed the plan, they needed a way to identify the metallurgy after the block was poured, thus the fabled "stamp" But engineering soon realized that the same block part number could posess one of 3 different mettalurgical blends. Because of this, it was near impossible to trace or efficiently logistically locate castings from pourtime to end customer use, as well as service parts orders.

So it was abandoned, because with the original idea, you wouldn't be able to call any GM parts office & locate a "nickel 010 block", because there was not a specific part number associated with it. Parts are organized by part numbers, not core stamps.

Now, to straighten this out, they did change the casting part number to correspond with the metallurgical content. This is true for only older blocks (pre 71) Blocks after that just used the same sand cores as the older ones until pattern changes were made, which will give false hope to many.

Hinging on that, many cores were interchangeable. Today, error proofing measures have been installed, and it is impossible to assemble mismatched pieces without destroying a section of the core."

Skip FIx

Well Known Member
I only got married in '79. We both usually get the date oin October off by a day. One year I was out at the track as we had a nice cool front blow in for some good air. I remembered it was our anniversary and went home a little early she had it wrong. My wife really into only 1 horsepower at a time. But I think her horse hobby costs more than my car hobby!