[C1] Engine stamp info
Thread Starter
8th Gear
Joined: Jan 2023
Posts: 8
Likes: 0
Engine stamp info
Newby here, I am trying to figure out my engine stamp info....not finding what I am looking for so I come here for help.
Have a 1961 Corvette
Block Casting # 3756519 seems correct
Stamp # HDK F0425M Flint, April 25th Mexico ?
What is the HDK ? found HD info, but the "K" I cannot find.
Any help appreciated
Red
Have a 1961 Corvette
Block Casting # 3756519 seems correct
Stamp # HDK F0425M Flint, April 25th Mexico ?
What is the HDK ? found HD info, but the "K" I cannot find.
Any help appreciated
Red
Race Director
Joined: Oct 2000
Posts: 12,667
Likes: 3,123
From: Shamong, NJ
The "M" after the assembly date, identifies the engine, not the "HDK" before it.
"F0425M" decodes as a Flint built (F) engine assembled on April (04) 25th (25), and the "M" identifies it as is a 2bbl, manual trans, 283 out of a Chevrolet truck. The "M" suffix code was used for 56-57 265/155 truck engines, 58-62 283/160 truck engines and 63-64 283/175 truck engines. The 3756519 block was used for cars and trucks from 1958 to 1962, so your "M" code engine is out of a 58-62 Chevy truck. To determine exactly what year truck it came out of, the casting date on the engine rear flange, on the opposite side of the block from the casting number, needs to be known.
What the "HDK" is I don't know, but it could be an engine rebuilder's mark, or some mark put there by someone else for some reason. In 61 only Corvette engines, and some high horse passenger car engines (mainly 348's and the handful of 409's built) got a VIN stamp. Truck engines didn't get VIN stamps till it became Federal law in 68, so the only thing usually stamped on an earlier truck pad would be the code for the assembly plant, the month, day and the letter identifier for the engine suffix code.
A picture of the pad, might shed more light on what the "HDK" is.
Welcome to the Forum!
"F0425M" decodes as a Flint built (F) engine assembled on April (04) 25th (25), and the "M" identifies it as is a 2bbl, manual trans, 283 out of a Chevrolet truck. The "M" suffix code was used for 56-57 265/155 truck engines, 58-62 283/160 truck engines and 63-64 283/175 truck engines. The 3756519 block was used for cars and trucks from 1958 to 1962, so your "M" code engine is out of a 58-62 Chevy truck. To determine exactly what year truck it came out of, the casting date on the engine rear flange, on the opposite side of the block from the casting number, needs to be known.
What the "HDK" is I don't know, but it could be an engine rebuilder's mark, or some mark put there by someone else for some reason. In 61 only Corvette engines, and some high horse passenger car engines (mainly 348's and the handful of 409's built) got a VIN stamp. Truck engines didn't get VIN stamps till it became Federal law in 68, so the only thing usually stamped on an earlier truck pad would be the code for the assembly plant, the month, day and the letter identifier for the engine suffix code.
A picture of the pad, might shed more light on what the "HDK" is.
Welcome to the Forum!
Team Owner
Joined: Feb 2003
Posts: 54,073
Likes: 9,398
From: Sitting in his Nowhere land Hanover Pa
2024 C2 of the Year Finalist - Unmodified
2015 C2 of Year Finalist
The suffix code is “M” the decides to a truck engine there never was a vin stamp on an engine with less than 300 advertised horse power until 68. HDK was stamped after the engine left any GM assemble plant so it’s meaningless unless the guy you bought it from initials are HDK
Team Owner
Joined: Feb 2003
Posts: 54,073
Likes: 9,398
From: Sitting in his Nowhere land Hanover Pa
2024 C2 of the Year Finalist - Unmodified
2015 C2 of Year Finalist
Well most would say ask questions before you buy and not after. It could built to 275hp spec but it didn’t leave the factory that way
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Team Owner
Joined: Jul 2006
Posts: 22,167
Likes: 4,172
From: Kannapolis NC
The suffix code is “M” the decides to a truck engine there never was a vin stamp on an engine with less than 300 advertised horse power until 68. HDK was stamped after the engine left any GM assemble plant so it’s meaningless unless the guy you bought it from initials are HDK
Team Owner
Joined: Feb 2003
Posts: 54,073
Likes: 9,398
From: Sitting in his Nowhere land Hanover Pa
2024 C2 of the Year Finalist - Unmodified
2015 C2 of Year Finalist
Vin derivative stamps on engine pads for Corvettes started in late Dec of 59 for the 60 model year at the same time the vin plate moved from the door sill to the steering column. That was for all horsepower from 230hp 283's all the way up to and including fuel injection. Engine pads were stamped with vin derivatives on all Corvette engines after that. The below picture is an example for a 61 283 230hp.
Race Director
Joined: Oct 2000
Posts: 12,667
Likes: 3,123
From: Shamong, NJ
As I said in my previous post, the suffix code is the "M" after the "F0425", and is what identifies it as a truck engine. IF it was the original engine, it would have a portion of your VIN stamped in the area where the "HDK" is stamped. That "HDK" was NOT stamped on the pad by GM, and as I said in my previous post, is more likely something stamped by someone like an engine rebuilder as a warranty identifier, or by someone for some other unknown reason.
On the right (passenger side) REAR of the block, on the flange that the trans bolts too, and opposite of where the block casting number is, is where you will find a block casting date. This date will be made up of a letter for the month (likely a "D" for April, one or two numbers for the day of the month, and a single number for the year (such as a "1" for 1961). With the date it can be determined what year engine it is.
or number opposite block stamp
Again, appreciate your help
Again, appreciate your help
Race Director
Joined: Oct 2000
Posts: 12,667
Likes: 3,123
From: Shamong, NJ
Do you like the car, does it run and look good, then don't worry about it. Drive it and enjoy it. Face it, very few 60 year old Corvettes still have their original engines, even many of those with the "correct" and "matching" numbers stamped on the pad.
Thread Starter
8th Gear
Joined: Jan 2023
Posts: 8
Likes: 0
follow up question .... I get that engine "was" from truck @ 160HP
When rebuild was done they used correct parts
it was added to this block 3756519
and correct cylinder head 3739653
and correct dual quads 2626S & 2627S
Would this not get HP close to the 270hp as if it had come from factory ? or somewhere close to that?
When rebuild was done they used correct parts
it was added to this block 3756519
and correct cylinder head 3739653
and correct dual quads 2626S & 2627S
Would this not get HP close to the 270hp as if it had come from factory ? or somewhere close to that?
Le Mans Master
Joined: Feb 2014
Posts: 8,897
Likes: 5,435
From: Richardson Texas
follow up question .... I get that engine "was" from truck @ 160HP
When rebuild was done they used correct parts
it was added to this block 3756519
and correct cylinder head 3739653
and correct dual quads 2626S & 2627S
Would this not get HP close to the 270hp as if it had come from factory ? or somewhere close to that?
When rebuild was done they used correct parts
it was added to this block 3756519
and correct cylinder head 3739653
and correct dual quads 2626S & 2627S
Would this not get HP close to the 270hp as if it had come from factory ? or somewhere close to that?
Team Owner
Joined: Feb 2003
Posts: 54,073
Likes: 9,398
From: Sitting in his Nowhere land Hanover Pa
2024 C2 of the Year Finalist - Unmodified
2015 C2 of Year Finalist
I am going to say you will be disappointed either way. you can ask the seller for any paperwork or receipts from the engine build to see what parts where really used. if you have access to a inspection camara you can stick it down the spark plug hole and see what type of pistons were used.
Racer
Joined: May 2000
Posts: 482
Likes: 230
From: San Diego CA
2024 C1 of the Year Finalist - Unmodified
follow up question .... I get that engine "was" from truck @ 160HP
When rebuild was done they used correct parts
it was added to this block 3756519
and correct cylinder head 3739653
and correct dual quads 2626S & 2627S
Would this not get HP close to the 270hp as if it had come from factory ? or somewhere close to that?
When rebuild was done they used correct parts
it was added to this block 3756519
and correct cylinder head 3739653
and correct dual quads 2626S & 2627S
Would this not get HP close to the 270hp as if it had come from factory ? or somewhere close to that?
Bob
59 245hp
waving in San Diego