Deciphering Engine Plate

[YeOldeTruck]

My truck is a bit of a mutt so I’m trying to track down as much information as I can. I believe the frame and drivetrain are 78 K20 and the cab and bed are GMC 73 C20 (per VIN and title). However, an interesting wrinkle is that it is a 4x4 and has a 454 (I think) which doesn’t seem to be a factory option from the service manuals I’ve seen.

Anyways, this plate is on the underside of the engine. Anyone know how to decipher it?

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[YeOldeTruck]

Bump

 

[Bextreme04]

Not really anything to decipher... also I can't read the part number in the picture. Its a plate that shows it was a re manufactured engine at some point. Based on the different frame/cab/years that you have found so far, I wouldn't really trust anything as factory or original. If you want to know what engine/trans, or other parts you have, take pictures of casting numbers and whole components and post them here. Block casting number will tell you original application and size of the engine.

 

[QBuff02]

that's a general motors remanufactured tag. standard bore and the crankshaft rod and main journals are ground .010 undersized. The only give away in that picture that it might be a 454 is the 7 4 on the block next to the tag. post some better pictures of the engine and such and try to find some casting numbers if you can. that will go a long way in determining what you have.

 

[YeOldeTruck]

that's a general motors remanufactured tag. standard bore and the crankshaft rod and main journals are ground .010 undersized. The only give away in that picture that it might be a 454 is the 7 4 on the block next to the tag. post some better pictures of the engine and such and try to find some casting numbers if you can. that will go a long way in determining what you have.

Thanks, this is all helpful because I don’t know much about tracking this down. Here’s some more pictures of the engine.

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[YeOldeTruck]

Also a few casting numbers I found easily but they aren’t on the engine block directly.

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[YeOldeTruck]

Not really anything to decipher... also I can't read the part number in the picture. Its a plate that shows it was a re manufactured engine at some point. Based on the different frame/cab/years that you have found so far, I wouldn't really trust anything as factory or original. If you want to know what engine/trans, or other parts you have, take pictures of casting numbers and whole components and post them here. Block casting number will tell you original application and size of the engine.

Best I can tell the P/N is 12353944.

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[Bextreme04]

Well, that engine part number comes back as a GM re-manufactured engine for a 1985-1990 square body or van. It is definitely a 454, since that is the only factory big block you could have as a reman for those models and years. Unfortunately, that also means you have a bunch of unnecessary emissions crap on that motor that wouldn't be on an original 70's 454. The engine block casting number will be on the back of the block above the transmission mounting point. You can also find the cylinder head casting number under the valve covers.

 

[YeOldeTruck]

Well, that engine part number comes back as a GM re-manufactured engine for a 1985-1990 square body or van. It is definitely a 454, since that is the only factory big block you could have as a reman for those models and years. Unfortunately, that also means you have a bunch of unnecessary emissions crap on that motor that wouldn't be on an original 70's 454. The engine block casting number will be on the back of the block above the transmission mounting point. You can also find the cylinder head casting number under the valve covers.

Thanks, that’s helpful. Here’s a few photos of the markings on the bottom/back of the engine.

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[Bextreme04]

The GM 7.4 marking means it is definitely a 454. You are almost in the right area on the back of the block. On the top of the flat flange that the transmission bolts to, there should be a cast in number. Here is a better description of where to find everything. https://www.mortec.com/location.htm

 

[YeOldeTruck]

The GM 7.4 marking means it is definitely a 454. You are almost in the right area on the back of the block. On the top of the flat flange that the transmission bolts to, there should be a cast in number. Here is a better description of where to find everything. https://www.mortec.com/location.htm

So would I be able to see it from the top of the engine or under the truck? I looked everywhere I could under the truck but can give it another go. The Mortec link didn’t provide enough detail for a noob like me. Going to keep trying!

 

[DanMcG]

So would I be able to see it from the top of the engine or under the truck?

It's pretty hard to see but it's on the top of the block basically behind the driver side valve cover. I've used the camera on my phone and blindly take pic's until I capture it.