I have a 1966 mustang with an original build sheet showing the VIN 6T08Axxx and a date code of 20K (October 20, 1965). I removed the starter to see the engine block date, which was 4K24, (Oct 24, 1964). The manifold intake date is 4J23 (Sept 23, 1964). I have read that in the busy production times, sometimes parts were left over and used in later vehicles. What I am wondering is if it is possible that the engine is original, even though the date precedes the car manufacture date by a year? I have assumed the engine was replaced at some time, because the date is so different. Anyone have any knowledge of engines and date codes differing by more than a couple of months of car manufacture? Thank you.
It is quite possible that you have the original motor. The same motors were used in all of them. The date you're seeing is the casting date. There should be an ID number someplace that matches your door plate.
Thank you, but it is my understanding that there are no ID numbers on mustang engines (pre 1968) other than the casting number and date code next to the casting numbers. Thus, there are no "matching numbers" mustangs before 1968. Everywhere I read I find that the engine should pre-date the car manufacture date by 2-3 weeks, but have also read that there are times when older parts were used on cars if they were over-manufactured.
The previous owner, who had the car over 25 years, had no knowledge of the engine being replaced, but who knows what might have happened prior to then. I am just wondering if it is POSSIBLE that the car was produced with an engine that was a year older than the build date? Thanks for any insight.
Since they built over 1 million Mustangs in the first two model years, the chances of an engine lying around for a year, before putting it in your car, are slim. IMHO, you do not have the original engine in your car.
Zaikur, as far as I know, VIN stamping on engines was not done on regular production Mustangs until the 1968 model year.
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Thank you. That has been my opinion as well until I read an article about stockpiling, but it did not specifically mention engines. It is still the A code engine, so it is correct, just not the correct year. Of course I did not find this out until I took the starter off the car after I purchased it. It runs well, so I am happy about that part!
I contend, that for a nation to try to tax itself, into prosperity, is like a man standing in a bucket and trying to lift himself up by the handle.
—Winston Churchill
The basic casting number by the starter could be the same for quite a while, just the casting date changed. The block assembly date code is STAMPED on the front, just in front of the center of the left cylinder head on a small flat spot. It will be later then the casting date. Compare the assembly date on the front to the casting date by the starter to see how long it took them to assemble it. I doubt it was very long.
It does appear you have an earlier engine since the 65 block was a C5AE. But that block could have been an original one in 65, 66 or 67 so it wasn't something than always changed every year.
Buy the Bob Mannel book, The Ford Small Block V-8. It tells you all the numbers and variations that were built, and when, for any of the 221/260/302 engines. Unfortunately, it doesn't cover 351s.
Thank you. When you say stamped, is it raised like the casting number and the manifold date code? Our engine was painted before we got it, but where I can see the front there are no numbers. We have power steering, so maybe the place it is mounted covers where you are talking about. Or do I have to have the valve covers off? Is it possible for you to send me a picture of where it should be? Thank you so much!!!
The stamping is depressed into the cast iron so it could fill up with paint. Its in front of the valve cover stamped in a fore-aft line parallel to the crankshaft. I don't have an engine that I can easily take a picture of at the moment but how about a picture from the Ford Small Block V8 book? Hopefully you can recognize the location from this zoomed in shot. This date is for 1963 but its in the same place for later years.
1966 mustang engine date code question 
