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I'm going through the affirmation process with Al Grenning and can't help but wonder if he's the single authority on C2 engine stamp pads, etc. CCAS seems to be mostly a one man show and when he judged my car in 2013, he appeared to be in his 70s. Who will take the reins? Unfortunately for me, my stamp pad has inexplicable markings, but several respectable experts weighed in during a recent BaT sale attempt with opinions that it is a factory stamp - some privately and some during the auction. Now I have to pony up for CCAS affirmation on a short timeframe before leaving town for the summer.
My stamp pad was never challenged during BG Survivor or NCRS flight judging over 10 years ago, and the engine has been untouched since then. Some of you likely followed the auction and know my car has complete documentation from the day it left the factory, so I'm anxious to hear Al's take on it. I've been told (and read) there were up to 3% of engine blocks in 1966 that required "grind outs" due to defects on the pad. Mine is one of them and now I have to prove it. These old cars can sure be surprising!
I guess nobody has strong opinions on this topic. Authentication of these cars seems to be an important aspect of valuation, and the next generation needs to be able to provide this service. Who will it be?
Sounds familiar to me. My first NCRS regional the stamp was questioned however asked top members of my chapter and even CC (National Judge for 63/64) who all agreed it was a valid re-stamp. The judge on my car said NO and would not back off, top flight so never voice an objection. To avoid that again got CCAS affirmation, never questioned again. Al collect a lot of data, so I hope it gets passed onto somebody
I guess nobody has strong opinions on this topic. Authentication of these cars seems to be an important aspect of valuation, and the next generation needs to be able to provide this service. Who will it be?
Jonathan Herrick. On this site as DKM-106.
He has the L89 registry and has tracked these cars for a long time. He has a huge database of trim tags, stampings, etc
He knows the C3s really well.
This stamp pad was affirmed by CCAS Saturday as factory original. The broach marks are unusual as are horizontal marks at the vin derivative. My lesson is the broach marks are much less important than the stampings.
In no way am I disputing any conclusions from the experts. But the pad grooves always fascinate me. I don't see any of the original longitudinal broach marks. The long, roughly 30* small grooves appear from something like a long sanding block, not a broach and there's some cross hatching. Decking cutters I've seen are 6-8" diameter which show the cutting radius. I'm curious if the experts explained how the broach grooves were removed (which would be a fair amount of material). It looks like the VIN horizontal scratches were done after other scratches. Again, no dispute here, just a curious engineer that happens to own a machine shop. Larry
This stamp pad was affirmed by CCAS Saturday as factory original. The broach marks are unusual as are horizontal marks at the vin derivative. My lesson is the broach marks are much less important than the stampings.
WOW – I had to read this several times because I can't believe this is determined to be factory. There are so many oddities from what I've seen of a factory grind out, let alone a typical mark. Both the engine and VIN stamps appear to have other character marks beneath. Perhaps an engine stamp might have been redone before it left Tonawanda, but the VIN wouldn't have been there to be affected. If a VIN required grinding out, they wouldn't obliterate the engine stamp - or restamp it with Tonawanda style characters. Lastly a GM machine shop wouldn't have reground the cylinder surface with all those marks going in different directions – I imagine they'd use a surfacer with uniform track marks.
I guess nobody has strong opinions on this topic. Authentication of these cars seems to be an important aspect of valuation, and the next generation needs to be able to provide this service. Who will it be?
You have an interesting stamp pad. I assume that Al's opinion was that the engine was decked at Tonawanda and then stamped. Broach marks are important for a stamp pad, but when I am assessing the probability of a stamp being original, they carry less weight than the vin stamp and other criteria. As Joe mentioned, I offer validation services on 1963-1972 Corvettes. You can check it out here: https://c3site.wixsite.com/corvette-validation I have built a software platform powered by AI as well, that provides a forensic analysis report based on a set of specific criteria.
Has anybody figured out how this actually happened. It doesn’t look like any grind out that I have ever seen. Does anyone
know how this actually occurred.
What I can say is based on the extensive documentation available, the stamp pad was last touched at the factory prior to delivery, likely St Louis according to the typical build sequence and the vin derivative grind marks appearing to be on top of the others. Maybe an original vin stamp was so light they chose to carefully grind it to avoid the Tonawanda restamp? I've certainly learned a lot about the stamping process and am satisfied to have CCAS affirmation. I'll accept it as a unique birthmark.
CCAS affirmation
