What's That Engine?

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Mrmarcdude

Not-quite-so-new-guy
Nov 16, 2020
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Hey Everybody,

New guy here. Just picked up a 3.8L 86 Cutlass and it's had the engine replaced at some point (distributor in the front). Combing over the engine as best I could, I've identified two serial numbers. Was wondering if anybody could take a crack at what vehicle this motor belongs to? Year? Make? Model?

There is a raised serial number cast into the block on the drivers side that reads 25514290. Just behind that, on a flat vertical boss it's stamped with 3fm402265. Any help is greatly appreciated.
 

jiho

Royal Smart Person
Jul 26, 2013
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It's a "VIN A" Buick V6. 25514290 is the block casting revision number. The one in my '83 Malibu had that same number.

3FM402265 is the engine serial number. "3" means the factory put it in an Olds. "F" means that was an '85 model year Olds, and "M" means that Olds was assembled at the Lansing (MI) factory. Compare "FM402265" with the last 8 digits in the VIN on the plate at edge of your dashboard, visible through the windshield at the driver's end. If those digits are all the same, the motor came in the car from the factory. Otherwise it was swapped.

If your Cutlass is an '86, an '85 motor would be a swap. But that was the base model motor in the G-body Cutlass for some years, so it likely was just a replacement "long block" for the motor the car came with.

Someone else might know what the "4" in "402265" means. I think it indicates the model, but I don't know which model.
 
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Doug Chahoy

Comic Book Super Hero
Nov 21, 2016
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An article I just read about GM assemblies said that because assemblies such as engines built in one state could take awhile to hit the assembly line. That engine could have been built in late 85 and installed in an 86
 
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Mrmarcdude

Not-quite-so-new-guy
Nov 16, 2020
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Thank you! It was definitely replaced at some point as the gentleman I bought the car from bought it from the original owner. The owner had it replaced back in the mid 2000s. I really appreciate the info.

I'm trying to hunt down the proper spark plugs for this thing. I pulled out some long thread r44's, but everything I'm searching for has the short thread r45's for the 3.8. The transmission was also swapped to a turbo 250 at some point.

Whoever worked on it last mixed up vacuum lines, didn't torque bolts down, etc. So I'm just assuming he could have installed the wrong plugs. Hell, half of the plugs were literally finger tight. He ran them down until there was a little resistance, then stopped.
 

69hurstolds

Geezer
Supporting Member
Jan 2, 2006
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The last 8 letters/numbers should match the VIN of the car it was originally mated to.
Federal law mandated that the engine be stamped with the VIN derivative. jiho was correct in that is is an 85 Oldsmobile from Lansing with the last 6 of the VIN as 402265.

It matters not when or where the engine was produced. Those numbers/letters are stamped on the ID pad of the engine when the order sheet dictates a 3.8L is to be installed in whatever car the paperwork says and the "official" marriage of the VIN and that particular engine or transmission is picked. There's a tickler system somewhere that designates when the VIN is assigned to an order, and then everything about that car revolves around that VIN. The production office took care of all that and then parts were assigned for that model, etc., etc. Anything that needs stamping with a vin (frame, engine, etc.) gets stamped once that part gets pulled/assigned to that VIN order. The production office goes right down the line on the next sequential number when assigning VIN's. First come, first serve. You COULD NOT pick your VIN number. Maybe if you had $$$ you could. Ask me how I know. I was trying to get one with a "442" in it somewhere. I just thought it would be neat.

I can't speak for all cars and assembly plants, but I watched several 82 Corvettes get built when my dad still worked for GM. The VIN plates were stamped somewhere else, and they installed them on the "birdcage" (metal surround where the people go) with a power rivet gun. Nothing special. Pop- Pop! Done. Someone from QA would check the numbers against a sheet before it was installed and someone else checked the plate against the build sheet after it was installed.

Never in my life have I ever seen the VIN not match on an engine to the car it was born in. Could it happen? Sure it could. But remember in '77 or so when that Olds got that Chevy engine that started the whole "corporate" engine thing? Nobody wanted another Federal case. And if the factory mismatched VINs, then it very well could be a Federal case.

As far as parts made, then used later, much later sometimes, it's just a fact of life. For instance, Hutch (aka oldsofb) gave me his old, original brake combination valve from his 87 442. Date code says it was built in July 85. Sometimes they used "Just In Time" production so the part build date would be a week or two prior to the car's build date, but that wasn't a big thing in the 80s. They didn't start building 69 H/O's until the end of March 69, but there's many H/O only distributors with January 69 build codes on them.
 
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69hurstolds

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Jan 2, 2006
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Hmmm. It does cost money to get the VIN you want. 2021 Corvette has them. Personalized Identification number. Listed under RPO "PIN" - Customer Selectable VIN- $5,000.00!!!!!!
 
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