1970 Block Stampings

[Pat F.]

Alright C2 Guys have mercy on a C4 Guy.

A friend of mine recently had his engine taken out of his 1970 and he took the following pictures of various stampings. I could help him with the G30 as being a date code of July 3, 1970 and the Block Casting Number of 3970010 being for the small block 1970-71.

The other Block Stampings are unknown to me. My friend told me that he was told that the Stamping of M45 was placed by the foundry because the Block was a transition Block, meaning that the workers at the Foundry were constantly monitoring the composition of the Blocks and when it need to be changed they ran a series of test blocks and they stamped the M into the block so that they could monitor the composition. I never heard of such a thing, but what do I know?

He would appreciate any comments on the stampings on the Block, knowing that we know the date code and block number.

I know one of the stampings is a clock, but I do not know how to read it.

Any help would be appreciated.

[Terry M.]

Re: 1970 Block Stampings

Alright C2 Guys have mercy on a C4 Guy.

A friend of mine recently had his engine taken out of his 1970 and he took the following pictures of various stampings. I could help him with the G30 as being a date code of July 3, 1970 and the Block Casting Number of 3970010 being for the small block 1970-71.

The other Block Stampings are unknown to me. My friend told me that he was told that the Stamping of M45 was placed by the foundry because the Block was a transition Block, meaning that the workers at the Foundry were constantly monitoring the composition of the Blocks and when it need to be changed they ran a series of test blocks and they stamped the M into the block so that they could monitor the composition. I never heard of such a thing, but what do I know?

He would appreciate any comments on the stampings on the Block, knowing that we know the date code and block number.

I know one of the stampings is a clock, but I do not know how to read it.

Any help would be appreciated.

If you C4 guys think the C2 guys are going to help you with this -- well I am speechless. On the other hand when it comes to the earlier cars I can't tell the difference either, so you can be excused as well.

Now that I have taken my pound of flesh ... let's get serious.

The first photo M46 is not a stamping. It is a casting, and so is everything else you have posted images of. Is this image on the right hand (passenger's side for many of you) of the rear of the case? If it is -- it simply indicated the cylinder case is a "test shot" of some type. Without the original foundry records, which we don't have, we will never know what the test was. There were hundreds, and perhaps thousands of these that found their way into all sorts of Chevrolet vehicles over a long stretch of time.

The second image is the casting number of the cylinder case 3970010 made by GM the mold number for that part of the mold is 22.

The third image is the time of the casting the D N T are the three shifts (Day, Nite & Third) and the arrow points to the Third shift (the overnight shift, if you will). The "clock" indicates the hour of the shift. All three shifts were ten hours long (note 10 dots). The clock starts at the Double dots, and the arrow points to the first hour. There were three ten hour shifts in the foundry. The molten steel had to be keep molten ALL the time. So this case was cast on the first hour of the night shift -- one might even say just after or around midnight. Of course the bad news is we have no date because of the M46 casting in place of the date. See how important all this was to the foundry? It all means Jack. I am not sure at what time the shifts changed and there was obviously some overlap for shift turn-over, so beyond early in the morning I can't tell you exactly what time of day this case was cast.

The fourth image 020 & 010 means that part of the mold is useable for cylinder cases bearing the casting number 3970010 and 3970020. I am at a loss for the G30 casting, and I know our resident Saginaw Metal Casting employee or John Hinckley (there are your C2 guys Pat) will have to help.

[Tom H.]

Re: 1970 Block Stampings

Interesting. Can't say I've ever heard this info. Thanks !

[Michael W.]

Re: 1970 Block Stampings

The fourth image 020 & 010 means that part of the mold is useable for cylinder cases bearing the casting number 3970010 and 3970020.

These are the two markings that gave birth to the legend of high tin/nickle blocks.

[Terry M.]

Re: 1970 Block Stampings

These are the two markings that gave birth to the urban legend of high tin/nickle blocks.

There I fixed it for you Mikie.

BTW: I have missed you at the meets lately. They are less fun without you there.

[Pat F.]

Re: 1970 Block Stampings

Terry, thanks for the informative information. My friend was amazed on quickly he got an answer.

Now we are down to the G30 stamping.

I just know that some of the C2 guys will give us C4 guys an answer.

[John H.]

Re: 1970 Block Stampings

Terry, thanks for the informative information. My friend was amazed on quickly he got an answer.

Now we are down to the G30 stamping.

I just know that some of the C2 guys will give us C4 guys an answer.

Pat -

That "G30" is on a bulkhead pattern, so it's not a date - it's a pattern number. There won't be a typical block casting date, as this is an "M" block, and there's no way to identify the casting date of an "M" block. The 3970010 was a very high-volume block casting, and was in production continuously from mid-1969 through late 1979.

[Pat F.]

Re: 1970 Block Stampings

Terry and John, as usual, thank you very much for the information. I have passed it on to my friend who also sends his thanks.

[Mark G.]

Casting Article.jpg

[Terry M.]

Re: 1970 Block Stampings

[ATTACH=CONFIG]46115[/ATTACH]

Mark,

I knew we could count on you for all the answers. Thanks.

[Pat F.]

Re: 1970 Block Stampings

Mark, thanks for all the detailed information you provided. My friend will really be impressed on the conversations that his block created.

This Technical Board is such a wealth of information and I thank everyone who answered my question.

[Kenneth H.]

Re: 1970 Block Stampings

Mark, I have an M block in my '70 LT1 and was wondering if I could get a better copy of the article that you posted. I tried to print it from your picture, but it was pretty grainy.

Thanks.

[Cecil L.]

Re: 1970 Block Stampings

MCode 1 .jpgM code castings.jpg