Proper engine for 72 T - Top

[robert erb]

Need to buy a motor for my 72 t-top LS5 and I would like to get it as close to the original (numbers matching) as possible. I know I need a block casting # of 3999289 and I am aware of the date code, but I am not sure how the VIN # of the car comes into effect. Any help would be greatly appreciated.

[William C.]

Re: Proper engine for 72 T - Top

The VIN of the car can be tracked to the assembly date of the car, an it is reasonable to assume the engine would be built froma couple of weeks to a couple of months before the car to allow for transportation, and some staging within the Car assembly operation. Knowing the window in which the engine shuld be built then leads to fairly logical conclusions about dates on tiems such as blocks, heads, and intake manifolds that had to be available prior to engine build. Note that the carburator was added at St Louis, and is a part of the car buld, and not uniformly consistant with engine build dates. I once owned a 3 star original '72 car (454 with A/C)) built the last week of '72 production and it had a December '71 carburetor on it. Very early and very late production cars can have some unusual combinations of parts, but all must be consistant with the overall sequence of build.

[robert erb]

Re: Proper engine for 72 T - Top

Thank you for responding Bill. I am somewhat aware of the date code the block needs to be when compared to the VIN ( six month rule). I think the last six numbers of the VIN are to be stamped on the tab of the block, but how important is this during judging. And, what do numbers like GM10T mean. I have a few books that talk about chevy casting numbers, but they do not address these questions. Would love to here from any who can help. Thanks

[William C.]

Re: Proper engine for 72 T - Top

the GM10T is a code for the actual mold used for that particular block, T=Tonawanda casting, 10 is the number of the particular mold The VIN stamp is a judged item, I don't remember the points assignment, but you can get a copy of the scoresheets from Roy Sinor, the National Judging Chairman, he will email you a PDF file for the year you are interested in. (link from the NCRS home page)

[Chuck S.]

Re: Proper engine for 72 T - Top

The number of points assigned for the engine is not trivial, but a non-original engine car can get do OK if it has the correct type engine, and get even better if the engine was built during the preceding six months before the car was built.

The configuration (type), casting dates, and stamp pad are all judged separately, and in that order. For configuration its pretty much pass or fail for full credit allowed for configuration.

If the engine components all have suitable casting dates within the six month window preceding the car's build date, then more credit is received. Ideally, you would like the casting dates grouped closely within a several week period just as they would have been from the engine plant. A complete original engine would be the ideal choice rather than trying to assemble an engine from parts.

The last category, stamp pad, is the hardest. The pad surface finish is first judged to see if it is as it came from the engine plant...if it is not, you get a deduct. If the pad surface is satisfactory, then the stamps are judged.
There are two stamps...a machine or engine build stamp and a VIN derivative stamp. You can never get any credit for the VIN stamp if you don't have the original engine in the car, but you may be able to get some credit for the machine stamp if it happens to luckily fall in the six month period before the car was built...such luck typically doesn't happen in real life.

[Robert Erb]

Re: Proper engine for 72 T - Top

Thanks to both Bill and Chuck
Chuck. you write about a machine stamp on the engine. I do not understand what this phrase means, could you please explain it (is it the date the block was casted i.e. C 13 2)? Thanks also for having the time and patients for me.

[Chuck S.]

Re: Proper engine for 72 T - Top

On Chevrolet engines of that era, two separate "stamps" that were made at different times on the engine block "pad" that extends out in front of the passenger side head. These stamps were comprised of separate stamp characters that were arranged in the appropriate format in a hand-held rack of sorts, or "gang stamp". Once the assigned assembly worker had the gang stamp set-up, he placed on the pad and whacked the everylivin' heck out of it with a big hammer.

The first of these stamps was applied at the engine plant before painting, and is called a "machine stamp" by those "in-the-know". (I know because I'm a good listener, and I have heard those "in-the-know" call it such. )

The first character of the "machine stamp" identifies the engine plant; either "V" for Flint , Michigan (small blocks), or "T" for Tonawanda, New York (big blocks). The next four characters represent the day and month of production, and the final three characters is the suffix code, which identifies the model year, engine type, and transmission type.

The second stamp was stamped on the engine pad after that particular engine was assigned to a specific vehicle at the final assembly plant, and is called the "Vin Derivative Stamp". It will include the last several characters of the VIN, or serial number of the vehicle. The top/bottom positions of the stamps on the pad are different depending whether the engine is a small block or a big block

The way I interpret the NCRS judging literature, if you were so lucky as to find a replacement engine that had appropriate casting dates, an unmolested pad showing orignal broach marks, and a "machine stamp" that just happens to be for a Corvette built during the same six months as yours but with a different VIN, you will have managed to get as close as you'll ever get to the original engine by NCRS standards. Point deduction in this case ends up being pretty nominal by comparison.

Practically speaking, I believe you will be lucky to find a correctly configured engine with matching casting dates in the six months preceding your car's build date. Good hunting, and happy holidays.

[Chuck S.]

Re: Proper engine for 72 T - Top

"...and a "machine stamp" that just happens to be for a Corvette built during the same six months as yours but with a different VIN..."

I should have emphasized that this Corvette would also have to be equipped the same way as yours regards engine type, transmission type, etc...i.e. it would need to have the suffix code as your original engine to get full credit for the machine stamp.

That's why finding such an engine would be a long shot...it may have happened before, but I haven't heard about the experience.

[Robert Erb]

Re: Proper engine for 72 T - Top

Chuck, I want to thank you very much for the time and energy you spent explaining the different block markings. I now am somewhat better able to handle the hunting task.