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Ask Ted G. Your Own Question
Ted G.
Ted G., ASE Certified Technician
Category: GMC
Satisfied Customers: 6139
Experience:  20 years auto repair experience, ASE Master Tech, Mechanical Failure consultant, Expert Witness
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I have an older gh performance GM 7.4 L block with

Customer Question

I have an older high performance GM 7.4 L block with crankshaft. I would like to sell it and need to know how to properly identify it. I have photos of every angle and number stamped. Please advise
Submitted: 2 years ago.
Category: GMC
Expert:  Toolhut replied 2 years ago.

Hi, My Name is***** have over 20 years experience repairing vehicles. I am a ASE Certified Master Auto Technician. I am confident we can resolve your problem together.Please remember I don't know your skill level. I can't see, smell, hear, or touch the vehicle. It may take a few back and forth replies to get to a satisfactory resolution.I also try to give all of the information you may need expecting a positive rating. If there is any reason I cannot get a positive rating please let me know.

There should be a casting number on the top back of the engine where the trans bolts up.

BTW way what do you want for it?

Customer: replied 2 years ago.
Thank you Sam. I have limited experience and skill. Don't really know much except what I can read on the motor. I took photos of the transmission bolt up area. This is all I can see stamped. I have it listed on eBay for auction starting at $200. Including the crankshaft and hoist. Buyer pays for pick up and or shipping.
Expert:  Toolhut replied 2 years ago.

Tip the motor over. It is on the top by where the trans bolts up

Customer: replied 2 years ago.
Ok. well That's not going to happen. I have to look under the motor and its sitting in a uncomfortable place in my mother-in-laws place. I have to get under it and won't be as to do that until tomorrow or the next day. Once I have that I will revert.
Expert:  Toolhut replied 2 years ago.

The casting number needed for identification is on top

Customer: replied 2 years ago.
as the motor is sitting on this hoist its upside down? Well, I have to then get under the motor and take the pictures of the casting number. I will do this tomorrow.
Expert:  Toolhut replied 2 years ago.


Customer: replied 1 year ago.
Hi Sam, Here is the only number I can see stamped on the bottom of the engine. Is this what you are looking for? If not please let me know exactly what I need to be looking for and exactly where on the motor. Thanks.
Expert:  Toolhut replied 1 year ago.

I am attaching a link to Big Block numbers. Maybe this will help

Customer: replied 1 year ago.
Hi Sam, That link was absolutely of no help...sorry. I'm not skilled nor do I know what I'm reading or trying to read. From all the photos I've sent you that is all the numbers or stamping that is evident on the block. There is no six or seven digit number.
So, again, if you have any other idea of where to look, I've sent you every side and angle of the block with all the markings we can see. Can you figure it out with these markings?
Expert:  Toolhut replied 1 year ago.

OK. How about 2 or 3 digit codes

Customer: replied 1 year ago.
Negative...nothing on this block has any of the letters or number combinations. The closest is 334. Note: lots of 335 on your list but no 334 and thats stamped all over this block...any other ideas?
Expert:  Toolhut replied 1 year ago.

My suspicion is that it is out of a 454SS truck sold in the 90's. I cannot locate the engine codes from the newer tonnawanda engines.

Do you have any other parts?

Customer: replied 1 year ago.
Crankshaft - that's it
Expert:  Toolhut replied 1 year ago.

I will opt out and see if someone has more information. PM me when you find out what you have as I may be interested and I will watch ebay for it.

Customer: replied 1 year ago.
Ok, its already on ebay...I named it "old GM 7.4L Block"
Expert:  Ted G. replied 1 year ago.

Hi, if that has a one piece rear main seal it is a block from a Chevy Performance 454 HO crate engine or short block. Here is a spec sheet on it as it came from the factory.