C3 head casting dates gone crazy!

[Tory S.]

On my original '75 L-48 I have heads 333882, but the casting dates are not the run of the mill alphanumeric ones with A-M being Jan.-Dec. then the day and year didgit.

One has M275 and the other having P1 2. Both are cast right next to the 333882. What on earth would thse be?

Thanks,
Tory
29912
'75 conv

[Harmon C.]

Re: C3 head casting dates gone crazy!

Could you be reading the mold numbers?

[Tory S.]

Re: C3 head casting dates gone crazy!

Hi Lyle.

Nope, I'm looking at the numbers right next to the head part number which is between the 1st and 2nd set of valve springs. Between the 2nd and 3rd set of springs is the casting clock right in the center of the head, then the GM casting or mold number between the 3rd and 4th set of springs.

This is a mystery. I'll shoot some pictures and post tomorrow. BTW, this is a one-owner car I ordered and bought new in April, 1975. The motor was never taken apart until my restoration. They are the heads that came on the car.

I know the dates of heads aren't judged, but I'd like to see if anyone could answer this mystery.

Tory

[Tory S.]

Re: C3 head casting dates gone crazy!

OK, here's the photos of the head casting dates for '75 original motor L-48. What dates couold these possibly be?

[Cecil L.]

Re: C3 head casting dates gone crazy!

Possibly part of this program. Doesn't explain the "P" code though.

[Tory S.]

Re: C3 head casting dates gone crazy!

Cecil, this is very interesting. The document you posted was dated 2005. Do you think the process was in use in the 70's?

[Terry M.]

Re: C3 head casting dates gone crazy!

Cecil, this is very interesting. The document you posted was dated 2005. Do you think the process was in use in the 70's?

I can tell you for sure that process was in place for cylinder cases in 1969 through 1972. I suspect it began well before 1969 and existed well after 1972, but WTFDIK?

I have to admit that is the first cylinder head casting I have seen with an M, but since we don't judge them we could have looked at hundreds of them without knowing it.




JK: I was exaggerating to make a point.

[Tory S.]

Re: C3 head casting dates gone crazy!

Cool, I've got a rare cylinder head with an M desigantion.

Any ideas about my other head with the P? Maybe it's even more rare?!

And why would one motor have two rare heads?

[David H.]

Re: C3 head casting dates gone crazy!

On my original '75 L-48 I have heads 333882, but the casting dates are not the run of the mill alphanumeric ones with A-M being Jan.-Dec. then the day and year didgit.

One has M275 and the other having P1 2. Both are cast right next to the 333882. What on earth would thse be?

Thanks,
Tory
29912
'75 conv

I believe GM issued a service bulletin in 1974 concerning the 333882 heads relative to overheating. Some 350/400 engines were built with a coolant blockage in the cylinder head. The SB indicates that engines that had been inspected for blockage have a white circular paint mark on the front of the engine block below the stamp date.

Perhaps the atypical numbers in the casting reflect GM testing different molds.

[Tory S.]

Re: C3 head casting dates gone crazy!

David,
Very interesting. Your information is a big help. Is there any source to find a copy of that Service Bulletin? It would be great to add to my documents!

Tory

[Brian G.]

Re: C3 head casting dates gone crazy!

The last time I replaced the valve cover gaskets on our '75, I noted that M65 was cast on the passenger side. January built car.

[David H.]

Re: C3 head casting dates gone crazy!

David,
Very interesting. Your information is a big help. Is there any source to find a copy of that Service Bulletin? It would be great to add to my documents!

Tory

My source is "Chilton's Mechanics' Handbook of Service Bulletins, 1970 to 1982 : Troubleshooting and Diagnosis" (Professional). I came across it in a used book store for $6 - price seemed right (paperback - about the size and thickness of a C3 Service Manual). It lists, by manufacturer, by year, service bulletins for American Motors, Chrysler, and GM.

The book does not list the number of the service bulletin, but because of the random appearance of titles, I believe they are in the order they were issued.

The titles of each service bulletin leave much to be desired. For example, the service bulletin that discusses the 333882 heads is titled "Too Hot to Handle". For that reason I just read through all the GM bulletins searching for Corvette or V8 related issues and marked-up the index.

The book also has a section that appears to be reprints of a monthly professional mechanics Q&A from some magazine. As-well-as a troubleshooting section.

If you want a copy of the page that discusses the 333882 issue, I can send it in a few days (I am traveling).

[Brian G.]

Re: C3 head casting dates gone crazy!

I found this. Scroll down to PART D..........

http://www.vette-vues.com/pdf_files/FactoryFacts.pdf

[David H.]

Re: C3 head casting dates gone crazy!

I found this. Scroll down to PART D..........

http://www.vette-vues.com/pdf_files/FactoryFacts.pdf

Correct. 74-T-6 That is the SB in the Chilton's book. Chilton's does NOT have the complete intro that you posted nor does it have the exit comments. It does have the step-by-step testing steps. Thanks.

[Tory S.]

Re: C3 head casting dates gone crazy!

David & Brian,

Thanks so much for figuring out my "M" code heads and getting me a copy of SB 74-T-6. Now the engine rebuild I'm doing has a new mark per the SB. I'm looking forward to getting the motor back in the car and waiting for the next judge to ask about the 1" white circle, so I can bring out the SB you posted.

Thanks again for all your help.
Tory