More On Engine Stamp Pads

[Michael H.]

And while we're on the subject of engine stamp characters, (we were?) I wanted to post a pic of a couple of handy tools that I made in the early 80's when I was judging at the Bloomington Gold event. As previously discussed in a series of posts several weeks ago, the character spacing and length of the group of characters is one of the keys to genuine original engine stamps. I posted all the math required to determine the length of the seven character group at that time but I don't think it meant much to most so I'll pass that part and give you the numbers.

The length of the small VIN character group will generally be in the range of 1.040"-1.050".

The length of the large engine plant character group will generally be in the range of 1.270-1.280".

These dim's will be that of the actual characters stamped into the block. There is some range, or plus/minus, but not a lot. The absolute mathematical minimum for each package would be 1.015" for the VIN and 1.218 for the engine plant stamp. The depth of the strike will have a slight effect on the length of the package and there was probably .020-.025" side clearance for the characters in the holder so it's possible for the total to grow another .050-.060" over the minimum, but typically, the numbers fall right into the range that I mentioned above.

If the package is 1/16" over/under these numbers, I would be seriously concerned. If it's 1/8" or more, it absolutely didn't happen at either of the above mentioned plants. (unlss it was one of those odd ball hand stamps)

NOTE: If the VIN stamp end character is a 1, the total dim would be reduced by .039" so the total package would be in the range of 1.001-1.011".

These dim's are correct for at least 62 through 67 and apply to all small and big blocks. May also be correct for earlier/later but I don't know for sure.

You can make the tools pictured in .5 hours from any thin sheet metal or aluminum. I used .018" aluminum and filed the openings to exact size on both.

[Michael H.]

The Tools *NM*

[Mark Milner]

Re: More On Engine Stamp Pads

(unlss it was one of those odd ball hand stamps)

Can you elaborate on handstamps?

[Michael H.]

Re: More On Engine Stamp Pads

Actually, that was supposed to be humorous as I've heard many tales over the years about how all the characters were stamped individually, one by one, no holder, and could vary in dim by at least .250". There was this one 63 owner at the Bloomington event a few years ago.......

I suppose the 64 F.I./T.I. engine stamp could qualify as being correct and not even come close as the last character of the engine code was individually hand stamped, usually over or next to the original last character. The FI engines were all stamped RF at Flint but were factory "restamped" RX when TI was added. If I remember correctly, that carried over to 65 also.

[Mark Milner]

Re: More On Engine Stamp Pads

I've seen engines with VINs and some with the last suffix character handstamped. Most of these were non-Corvette engines and long ago, mid '70s to mid 80s. I've always wondered why. They were frequently in junkyards or dumps or behind garages. This eliminates people faking them to make money at swaps, pass off as original, beat judging, etc., especially since many of these preceded such events. I've had a few theories, based on things a couple of guys I knew who worked at Chevy in St. Louis had said.

Theory 1. After it is off the line, engine quits or breaks. They can't fix it so they set another engine in, which of course was not stamped while going down the line, so it is stamped in the repair area.

Theory 2. While in inspection, the missing VIN is noticed and one is stamped.

Theory 3. The extra suffix is from an engine that went back to recycle as parts, and was rebuilt as a different model, so the extra or different suffix was stamped to indicate the new configuration.

Theory 4. Engine was replaced at the dealer and restamped the VIN per the requirements. However, I've heard that dealers rarely stamped an engine to match as the procedures called out for them to.

Thoughts, since you did spend time in St. Louis.

[Michael H.]

Re: More On Engine Stamp Pads

Theory #1 and #4 are accurate. Doubt #3 and #4.

While complete engine failure was not at all common at the plant, it did happen occasionally. The complete assembly would be changed but I really have no idea what happened to the engines that failed. I don't think Flint would rebuild anything as it was most likely more costly than scrap/write off. Maybe John Hinckley can help us on this one.

If an engine assembly was changed in the repair area of the plant, another complete assembly would be pulled off the rack and VIN stamped with a gang stamp tool, just like the one on the line. The stamp date would be in line with the replaced engine as most likely the car came down the line just hours before the 1st engine was installed.

In the 60's, "transfering engine stamp pad data" from the replaced engine/short block to the replacement block, under warranty, was part of the operation. I don't think it happened often though. If and when it did occur, it would have been done with individual hand stamps, not a gang stamp tool. I don't think I've ever seen one that was dealer stamped.

[Tom Dooley]

YES, It Works!

Just made a pair of your tools and tried them out. They work perfectly. I checked two old small blocks and the size was right on. Thanks.

[Edward M.]

Re: More On Engine Stamp Pads

Great idea. I remember watching Dale Pearman doing something similar when he would judge an engine stamp. He would put a piece of scotch tape over the engine pad, make a pencil rubbing of the stamp, pull the tape off and put it on a piece of paper, then take length and height measurements of the stamp with a vernier caliper that he carried with him.

[Michael H.]

Re: More On Engine Stamp Pads

The scotch tape method of observing/preserving the engine stamp pad characters began at Bloomington Gold some time in the mid 80's. We lifted a tracing off of every block that we judged and that tracing is/was kept on file with the rest of that cars records. It really did work well.

[John H.]

Re: More On Engine Stamp Pads

When assembly plant "pulls" came back to Flint Engine, they generally went on the hot-test stand first for evaluation (only took a minute or two), and the decision was usually made right there to either tear down for repair or to scrap. If it was a minor issue and was repaired, they hit the pad with the grinder and re-stamped it with the correct date and suffix and it went to the shipping dock (thus the "grind-outs" you've seen in Al Grenning's preentations). If it was determined that a major repair was required (complete teardown), generally they scrapped it. With one new engine coming down every twelve seconds, it wasn't worth the time and effort to do a major teardown repair.

[Michael H.]

Re: More On Engine Stamp Pads

Thanks John. That's what I assumed but I wasn't sure. I really couldn't see how it would be logical to rebuild one when they could assemble a new one in much less time and for a lot less money. Wonder what happened to the failed engines after Flint?