Engine-block Numbering.

Just like on the transmission casing and head, the engine block holds both casting and serial numbers.  We’ll do the casting numbers first for the sake of consistency.

The engine block’s component number is on the passenger side of the block, below and to the right of the distributor. It was tough to photograph around the various tubes, wires, and struts. As you can see, the Saginaw Metal Castings Operation’s “GM” is firmly visible in place. Still don’t know what the trailing number 6 represents, unless it is a mold code.  The component number is pretty clear (no before and after shot, as there wasn’t much I could do with limited space to clean it off):  3836233.


The block’s casting-date code is at a little lower latitude but to the left of the distributor, just above the flange on the block into which the oil pan bolts.  It is barely visible behind the starter motor—D255.  Following the casting-date pattern, that translates to D = April, 25 = 25th, 5 = 1945.  What?  That would mean Green’s engine block, the major component of the power train, had sat untouched somewhere for four years before the motor was assembled.  That doesn’t seem reasonable, but based on the number code from the GM  Vehicle Information Sheet I can’t come up with another explanation–unless I am not considering all the information.  I was not, it turns out, but I would still be interested in the opinion of someone with more experience.


The really meaningful number—the engine serial number—is stamped on a flat, machined boss on the passenger side of the engine, just below and beside the distributor and behind the oil dip stick tube, right where the Vehicle Information Sheet said it would be.  From the photos below you can see what a good brushing does for years of grime, but then this is where things get interesting.

I can’t quite decide what the number is because the stamp seems to use a capital I for a one. As I read it the engine serial number is quite clearly 05I22IIF55Z or 0512211F55Z.

Untangling this number is a little tricky.  The original motor of a 1949 truck would be a six-cylinder, 216ci (cubic inch) block and should have a serial number in the form of AAAA 000000.  For a 3600-series truck of that model year the prefix letters should be AGCA (Flint, Mich.) or AGCM (Tonawanda, N.Y.). Obviously that is not the case.

Instead, the serial number fits the pattern of a post-1954 motor:  0000000A00A.  If that is the case, then clearly Green’s original motor was replaced with a newer motor at some point before grandpa acquired him in 1973.  That’s a bit disappointing for the purist in me, but hey–it’s still the truck I loved and hated and drove.

Basing an interpretation of the number on Keith Hardy‘s work, the first numbers are the motor’s place in the factory production sequence–with an important caveat:  production numbering started with 1001 rather than 0.  That means this engine is the 511,210th General Motors Inline Six or “stove-bolt” engine to come off the line.  The F indicates the Flint, Mich. motor-assembly plant, the 55 represents an engine of the 1955 model year, and the Z means it is a standard engine.  So, rather than a 1949 216ci engine, that makes this one a 140-horsepower 1955 engine with a 235ci cylinder displacement.  It also means that the casting code on the block really means 25 April 1955 rather than 1945.

So, I’ve learned something important (thankfully, before tearing into the engine) but a bit deflating, as I hoped I had an all-original critter to work with. Life, I suppose, isn’t always clear cut.


One thought on “Engine-block Numbering.

  1. Pingback: Step 1a: Remove Radiator | The Green Truck

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s