Engine Serial Number does NOT Match Vehicle Identification Number

Q: Engine Serial Number does NOT Match Vehicle Identification Number

I was told buy one of my local specialty wrecking yards that the engine serial number and the VIN number didn’t always match from the factory. I’m inclined to believe him. My 1968 convertible was built in Los Angles and it’s all original. Nowhere in my delivery documentation does the engine serial number appear, only the VIN and Body Tag data. My engine and VIN don’t match – not even close. What’s the truth here?

A: Short Answer:
* The VIN on the car should match the VIN on the Engine (68 & up)
* The Engine Unit (Serial) Number was a separate number stamped on the Engine. This number has nothing to do with the VIN and appears with the VIN on the Billing History.
So, you are correct when you say the Serial Number and VIN did not always match. Infact, they will NEVER match because they are different/separate numbers. If the VIN on the front of the Block matches the VIN on the Dash, that is the original correct engine for that car. You can also search for the B’Cast Sheet in the car, that will also ‘authenticate’ your car.

A: Engine ‘Serial’ Number (manifest number) has no connection whatsoever to the Vehicle Identification Number. This number was used within the Plant for sequencing. There is a VIN stamped on the block however that should match the VIN on the car. This is stamped on the front, lower face of the block next to the timing chain cover (way down low near the harmonic balancer). People have tried explaining the purpose of the Engine Serial Number yet, nothing official from PMD has ever surfaced explaining when it was stamped and for what exactly it was used for. My guess is that is was used by scheduling/sequencing in order to match a particular engine with a specific car. The VIN would have most likely been stamped on the engine just prior to going into the car.

While working on the 1967, 1968, and 1969 Firebird Registry, I have found that you can have two cars with very close VIN numbers and yet, their Engine Block Serial Numbers are hundreds (or even thousands) of numbers a part. The Engine Serial (Unit) Number can be found on the Broadcast Sheet and the Billing History Sheet. Once the car was built, only the VIN had any significance since the car, engine and trans (manual only) were tied together through it.

Here’s another clue about the Engine Unit Number…. Looking through Service Bulletins, if an engine issue is addressed, most everytime the Engine Unit Number is mentioned. Example: for the 1967 Firebird w/Ram Air, there were two types of Engines; the 1st Type was used up through Engine Unit Number 646615. The 2nd Type started at 646616. Another Bulletin addresses the issue of 1967 Cylinder Head Oil Return Passage Modifications. It lists those vehicles involved including the range of VIN numbers and the Engine Production Number involved. Based on these examples, I would say the Engine Serial (Unit, Production, Manifest) Number was stamped onto the block somewhere within the Engine Assembly Line (not the foundary) along with the Engine Usage or Application Code (Two-Letter). I say this because the Foundary did not assemble the engine and had no idea whether it was going into a GTO or Firebird and if it was to be a manual or automatic Engine. Once the Engine Assembly Line received the Block, scheduling would have given it a specific Usage Code (2-Letter) in order for the Line to install the correct components on the Engine. Perhaps the Engine Unit Number was stamped at this point as well (according to scheduling/sequencing). At some point following the Engine Assembly, the Engine Unit Number was ‘connected’ to a VIN in order for the Plant to know which engine to ‘pick’ (or schedule) for a specific car.

I doubt that 30yrs ago, the assembly plants were using the same sequencing (or “Just in Time”) delivery methods we use today however, I’m sure they did have some sort of scheduling/sequencing system. Also remember that the engine had a large white label with red letters attached over the two-letter code stamped on the front of the block. This was another aid in determining usage/application for a specific engine (much easier to read this white/red label than to squint to see the 2-letter stamped code). Anyhow, That’s my ‘long-winded’ opinion on the issue of Engine Unit Numbers.

A: I used to work at the GM assembly plant if Fremont, CA. Engines came fully assembled less optional accessories. I’m sure this was the case at the sister LA pant as well. When the engine s/n number was stamped I don’t know. But I do know that sometimes there were problems with engines after they were installed and were swapped out at the plant. Also, sometimes there were problems like more bodies than engines (remember Buick engines going into Chevys – it’s true!), and they would grab whatever engine they could find and throw it in to keep the line moving. For what it’s worth!

A: …Yes, Engine usually came to most Final Assembly Plants fully assembled. (Not always the case though). In addition to a Forging/Casting Plant, there was also an Engine Plant where they were assembled. I’d guess this is where the engine received its Serial Number stamp. This number was used by the Final Assembly Plant (for the vehicle) to coordinate scheduling/sequencing for the engine to body. No matter what the situation in the Plant, I seriously doubt that they would grab whatever engine they could to keep the line moving. Especially after ’67. Engines were sequenced with the body and were controlled for many reasons. The case of the Chevy/Buick engines was unique and different. Despite the mix of engines, all still had serial/VIN numbers stamped on them and they matched a specific car. It’s not like there was just this big batch of engines and a Line Operator going.. “eenie meenie minee moe….”

A: The VIN got stamped on the block starting in 1968. I have a 1968 Ram Air I, and the VIN on the block, just to the left (looking at the front of the engine) of the timing cover, matches the last 6 numbers of the VIN. This number can”t be seen unless you remove the lower radiator hose from the water pump housing, or if you get a mirror and shine a light down by the harmonic balancer, you can see it

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