1968 BB block composition

[Charles F.]

I'm having an L36 block bored and have received some conflicting information. I was told, initially, that this block is cast iron and that higher horsepower big blocks have 20% nickel in them, making them stronger and more desireable. However, when I researched the casting numbers for the big blocks in 1968, they are the same throughout the various engines. This leads me to think that all the big blocks are the same composition. I'm confused .

Chuck Faillace

[Terry M.]

Re: 1968 BB block composition

Unless someone has done metallurgical analysis they just don't know. I don't know how the foundry would pour different alloys for the same casting number, but only having visited the Saginaw Metal Casting Plant so WTFDIK.

I have heard the same story (increased Nickel content for longer wear) about Oldsmobile cylinder cases, but that is a different situation for a different time and place.

[Mike G.]

Re: 1968 BB block composition

news to me. as far as i know they are pretty much all the same for the same casting number.

[Ridge K.]

Re: 1968 BB block composition

As a reference point, according to the 2000 GM Performance Parts catalog, the GM big block race engine has a hardness specification of 210 to 230 on the Brinell scale.

According to big name drag racers I have been around, none have mentioned a difference in the strength of the cast iron in various 427 Chevrolet engines.
Most Mopar engined drag racers identify 1976 as the changeover year for the cast iron "stength" of the cyclinder black material. 1977 and later Mopar engines are considered to have less strength. Mopar big blocks are sometimes desiginated as pre-1976.

Hopefully, some of our club's top mechanics can leave a comment.

[Clem Z.]

Re: 1968 BB block composition

that applied to some SBC not BBC as some SBC had a higher content of nickel to make them stronger

[Michael W.]

Re: 1968 BB block composition

that applied to some SBC not BBC as some SBC had a higher content of nickel to make them stronger

There's a story of some 0010 blocks having a 10% nickel content and that there's a mysterious code on the block to tell which was which. No idea what this code is, or if the story is true. I've tried playing a few backwards on my old turntable and listening for the secret message but no luck so far.

[John H.]

Re: 1968 BB block composition

At one point during the 10-year run of the 3970010 block, the percentage of tin and nickel in the alloy was increased (the tin for improved machinability, the nickel for improved bore surface hardness), at a cost penalty, to reduce warranty costs. The warranty improvement never materialized, and the added tin and nickel were removed as a cost reduction.

[Joe L.]

Re: 1968 BB block composition

There's a story of some 0010 blocks having a 10% nickel content and that there's a mysterious code on the block to tell which was which. No idea what this code is, or if the story is true. I've tried playing a few backwards on my old turntable and listening for the secret message but no luck so far.

Mike------


Under the timing cover and on the rear bulkhead of some small blocks will be observed a set of numbers like this:

010
020

Supposedly, the upper number represents the percent nickel and the lower number represents the percent of some other alloying metal. If I recall correctly, it's manganese. However, I don't think the numbers represent 10% and 20%, respectively. I think they represent either 1% and 2% or 0.1% and 0.2%.

I don't think this was ever done for big blocks, though. As far as I know, all of the big blocks cast at the Tonawanda foundry were of the same cast iron alloy. That may have changed when big block casting was transferred to Defiance, OH, but that didn't occur until 1984 so it didn't affect any original Corvette block.

[Cecil L.]

Re: 1968 BB block composition

Mike------


Under the timing cover and on the rear bulkhead of some small blocks will be observed a set of numbers like this:

010
020

Supposedly, the upper number represents the percent nickel and the lower number represents the percent of some other alloying metal. If I recall correctly, it's manganese. However, I don't think the numbers represent 10% and 20%, respectively. I think they represent either 1% and 2% or 0.1% and 0.2%.

I don't think this was ever done for big blocks, though. As far as I know, all of the big blocks cast at the Tonawanda foundry were of the same cast iron alloy. That may have changed when big block casting was transferred to Defiance, OH, but that didn't occur until 1984 so it didn't affect any original Corvette block.

Joe,
I'm surprised that you buy into that popular interpretation on the small block nickle content. I believe that the 010/020 on the front and rear of the block represents the last 3 digits of the block castings that used the same front and rear pattern molds. ie 3970010 and 3970020.That is what you find on just about any block chevy cast. Look under the timing cover of any chevy V-8 and you will find similar numbers representing the last digits of the current castings at the time which use the same front and rear patterns.

[Mark K.]

Re: 1968 BB block composition

As a reference point, according to the 2000 GM Performance Parts catalog, the GM big block race engine has a hardness specification of 210 to 230 on the Brinell scale.

According to big name drag racers I have been around, none have mentioned a difference in the strength of the cast iron in various 427 Chevrolet engines.
Most Mopar engined drag racers identify 1976 as the changeover year for the cast iron "stength" of the cyclinder black material. 1977 and later Mopar engines are considered to have less strength. Mopar big blocks are sometimes desiginated as pre-1976.

Hopefully, some of our club's top mechanics can leave a comment.

A little off topic perhaps, but that Brinell hardness (210-230) is similar to homogeneous armor used in naval applications during WW2. The face hardened armor utilized in the modern battleships of that era ran to about 600-700 on the Brinell scale - tough stuff indeed.

[Joe L.]

Re: 1968 BB block composition

Joe,
I'm surprised that you buy into that popular interpretation on the small block nickle content. I believe that the 010/020 on the front and rear of the block represents the last 3 digits of the block castings that used the same front and rear pattern molds. ie 3970010 and 3970020.That is what you find on just about any block chevy cast. Look under the timing cover of any chevy V-8 and you will find similar numbers representing the last digits of the current castings at the time which use the same front and rear patterns.

Cecil-------


Actually, at one time I thought the upper number (010) represented the last 3 digits of the casting number. However, over the years I've seen it stated in several references that I figured knew more about it than me that these represented the percentages of non-ferrous, alloying metals. So, I suppose I've just come to assume that they were right. Probably a bad assumption.

[Terry M.]

Re: 1968 BB block composition

I am sure Mark Gorney could give us the straight 411 regarding Saginaw cast small blocks. Mark, where are you?

[Mike G.]

Re: 1968 BB block composition

here are all the extra numbers on my 70 lt1 block if this helps. i was curious what all the other numbers meant but never curious enough to ask.

[Terry M.]

Re: 1968 BB block composition

I can tell you about the first one, or some of it, but for the rest you will need John Hinckley or Mark Gorney. I sent an email to Mark, but he is probably busy at work.

3970010 is of course the cylinder case casting number
GM speaks for itself
24 = the mould number
D = day shift
N = night shift
T = third shift
Since the pointer is pointing to the D, it means your cylinder case was cast on the day shift.
The circle is the hours of the shift. There were ten hours to each shift and the start is at the double dots. I am used to a pointer indicating which hour of the shift your case was poured -- but I don't see that.
The screw in the center of the "clock” is also an indicator of the shift. I can't recall the code, but it matters if the screw is a flat head, like yours, or a round head. Noland published the code and a lot of guys know it.