3782870 Iron Alloy

[Stuart F.]

Re: 3782870 Iron Alloy

Well let's see; I also know from "back in the day", block seasoning was an accepted method for consideration of a block suitable for over boring (machining) as opposed to a new block or one from a fresh engine tear down. How about that? any truth to it. Performance folks would take new blocks and let them sit outside in the elements for a period of time to gather a good coat of rust before machining them. Was that a waste of time?

Stu Fox

[Clem Z.]

Re: 3782870 Iron Alloy

Well let's see; I also know from "back in the day", block seasoning was an accepted method for consideration of a block suitable for over boring (machining) as opposed to a new block or one from a fresh engine tear down. How about that? any truth to it. Performance folks would take new blocks and let them sit outside in the elements for a period of time to gather a good coat of rust before machining them. Was that a waste of time?

Stu Fox

big shops heat cycled new blocks in a oven before machining them.

[Michael W.]

Re: 3782870 Iron Alloy

Mike -

I have been at this one from both ends for many years, and there are strong opinions on both sides of the argument. In all those years, I've never found one single shred of Chevrolet information to support the "010-020" high tin-nickel theory, but there is clear logic from the foundry folks that the 010-020 identification in the timing cover area simply indicates a common pattern for that portion of the block shared between the 3970010 and 3970020 blocks. I'm not a foundry expert, but I know enough about it to believe there's no way on earth that a high-volume casting operation like the Saginaw Grey Iron Foundry would dedicate a single cupola and holding furnaces to a special iron alloy just for certain 3970010 blocks, which were cast continuously from 1969-1979. If there was any truth to it, Chevrolet would have documented it somewhere, and it would probably have been mentioned in the Colvin books, as Alan had complete access to all of the detailed engine engineering records.

My background is in engine manufacturing, but not with the incredible production volumes of the Flint engine assembly plant. I cannot imagine any method of segregating a small number of slightly special castings and keeping them from becoming mixed with regular high volume production without issuing a different part/serial number or having an armed guard watch over them 24/7. Since these '010 020' castings have turned up in all sorts of low perf cars and trucks and NOT just SHP applications it infers that GM did not put any emphasis on keeping them segregated either.

The legend apparently started in the 70s and 80s when engine overhaul shops noticed than some blocks were more difficult to rebore than others. A source at GM stated that for a certain period of time the composition of the cast iron was altered slightly by adding more tin and nickel, each as an attempt to aid in initial manufacturing and enhance field durability. The actual amounts as a percentage were not stated, but have been rumoured to be .1%/.2%, 1%/2% or as high as 10%/20%. Obviously the 10% and 20% are not possible and even the 1%/2% variation is unlikely.

A rather prominent engine hotrodder made a huge leap of logic of associating the rumoured tin/nickel variations with the 010/020 pattern numbers and stating this as a 'fact' in his book. Voila- a legend was born!

It is true that some engines with 010 020 are more difficult to remachine, but not all such numbered blocks- some are 'easy' to machine. It is also true that some blocks without the 010 020 markings are hard to remachine.

I've heard that the only truly special SBC engine cases came in those '67s with factory BB hoods. (ducking for cover)

[Paul J.]

Re: 3782870 Iron Alloy

Well let's see; I also know from "back in the day", block seasoning was an accepted method for consideration of a block suitable for over boring (machining) as opposed to a new block or one from a fresh engine tear down. How about that? any truth to it. Performance folks would take new blocks and let them sit outside in the elements for a period of time to gather a good coat of rust before machining them. Was that a waste of time?

Stu Fox

The rumor I heard was supposedly regarding rusty school bus engine blocks. I've been told this by an old NASCAR engine builder and I've seen it mentioned on TV, but I would'nt bet the house on it being true, or that it would make any difference. Rust works from the surface, and it does'nt change the molecular structure of the metal beneath it.

As Clem mentioned, used blocks had the benefit of being heat cycled.

Paul

[Michael H.]

Re: 3782870 Iron Alloy

At some time in the mid 70's, Chevrolet offered, in service/over the counter, a bare block that was described as being "high tin content". It was shown in the HD pages of the "off road" parts list but not in the regular parts book for production vehicles.

That's the only block I remember that was any different than regular production. I would be very surprised if there was a difference in any blocks for any production use in the 60's, especially the early 60's.

[Clem Z.]

Re: 3782870 Iron Alloy

At some time in the mid 70's, Chevrolet offered, in service/over the counter, a bare block that was described as being "high tin content". It was shown in the HD pages of the "off road" parts list but not in the regular parts book for production vehicles.

That's the only block I remember that was any different than regular production. I would be very surprised if there was a difference in any blocks for any production use in the 60's, especially the early 60's.

never heard of this 10/20 stuff till the 70s with the 350 blocks. do any older pre 70s blocks have this on the block ???

[Kenneth B.]

Re: 3782870 Iron Alloy

The rumor I heard was supposedly regarding rusty school bus engine blocks. I've been told this by an old NASCAR engine builder and I've seen it mentioned on TV, but I would'nt bet the house on it being true, or that it would make any difference. Rust works from the surface, and it does'nt change the molecular structure of the metal beneath it.

As Clem mentioned, used blocks had the benefit of being heat cycled.

Paul

Leaving CI out to rust was a slow way to stress relieve the casting because rust creates heat slowly. We rough machined our CI patterns & then sent them out to heat treat to stress relive them so they would not warp. As to alloying iron in the ladle small foundries did it for ductile iron and to change hardness as in G30,G40 & G60 but big foundries would not do it that way too time consuming when pouring that much iron.

[Michael W.]

Re: 3782870 Iron Alloy

never heard of this 10/20 stuff till the 70s with the 350 blocks. do any older pre 70s blocks have this on the block ???

Other blocks from other generations are also found to have three digits cast into the surface under the timing chain cover. Amazingly, these three digits correspond to the three last digits of the block casting number.

Here's an example:

http://www.ebay.com/itm/l71-l72-l88-l89-427-corvette-camaro-yenko-3x2-3963512-/150622117426

look at the 512 and 272 cast on the front. This engine is a 3963512 cast in 1969, the same time frame when the 3955272 was being manufactured.

[Duke W.]

Re: 3782870 Iron Alloy

This applied to 461X heads, but back in the seventies some racers told me that even though Chevrolet had come out with "off road" heads, some sprint car engine builders preferred to start with a set of 461X heads, supposedly because they had a higher nickel content (which would be measured in tenths of a percent) than later heads, making the 461X heads tougher and more resistant to cracking. (I think tin aids machinability, but my metallurgy may be a bit hazy.)

I have no idea if this is true, but I do know that hand porting a set of 461X heads is a very time consuming process as the material is very tough.

I have no doubt that the gray iron alloys for various applications used by GM changed over the years and may have been different for, say, steering gear housings versus head or block castings at any given point in time. The iron needs to be tough (hard) for durabililty, but that makes it rough on tool bits and more difficult to machine.

I doubt that for any given block or head casting number that a different alloy would been used concurrently in production, but it's certainly possible that the alloy could have changed over time for a given casting number and with newly designed casting numbers.

Duke

[Joe L.]

Re: 3782870 Iron Alloy

This applied to 461X heads, but back in the seventies some racers told me that even though Chevrolet had come out with "off road" heads, some sprint car engine builders preferred to start with a set of 461X heads, supposedly because they had a higher nickel content (which would be measured in tenths of a percent) than later heads, making the 461X heads tougher and more resistant to cracking. (I think tin aids machinability, but my metallurgy may be a bit hazy.)

I have no idea if this is true, but I do know that hand porting a set of 461X heads is a very time consuming process as the material is very tough.

I have no doubt that the gray iron alloys for various applications used by GM changed over the years and may have been different for, say, steering gear housings versus head or block castings at any given point in time. The iron needs to be tough (hard) for durabililty, but that makes it rough on tool bits and more difficult to machine.

I doubt that for any given block or head casting number that a different alloy would been used concurrently in production, but it's certainly possible that the alloy could have changed over time for a given casting number and with newly designed casting numbers.

Duke

Duke-----


While cylinder block, cylinder head, intake manifold and exhaust manifold castings were of gray iron, most other cast iron parts were of nodular, ductile, or malleable cast iron. All of these are stronger than gray iron. For the most part, if not always, GM manufactured the different types of cast iron at completely different foundries.

Gray iron castings were manufactured at Saginaw gray iron (GM's largest foundry), Tonawanda, NY, and Defiance, OH.

Nodular iron castings were manufactured at the Saginaw Nodular Iron Foundry as well as Defiance, OH ( a foundry completely separate from the gray iron foundry but co-located).

Ductile/malleable iron castings were manufactured at Danville (Tilton), IL and, I believe, another foundry located in Saginaw, MI.

By the way, Saginaw Gray Iron has now been completely converted to aluminum sand casting. Defiance, OH gray iron and nodular iron foundries are the only cast iron foundries which GM operates in the USA. All of the other cast iron foundries have been closed. GM still operates a gray cast iron foundry in Toluca, Mexico and may have a nodular iron foundry there, too.

[Wayne W.]

Re: 3782870 Iron Alloy

My 67 427-390 used oil from day one and the original owner had it worked on under warranty. They installed rings. Didn't help. Then just before it went out of warranty he had it done again, this time with new heads. Still no help. Forward some years after I got it, I installed another set of rings because it still used oil. No help. Forward more years and I dropped a valve, so had the thing out and completely went through it. At that time, I noticed that it had hardness test marks all over it. I had never seen this many before, so I assume they tested it and culled it to the Corvette engine line. Now five sets of rings in 60K miles and still standard bore. Thats a hard block.

[Glen C.]

Re: 3782870 Iron Alloy

I just checked a disassembled bare 3782870 block mid 1963. There was an 870 above a 721 cast into the front of the block to the left of the cam and crankshaft bores, and a G17 in the same location, to the right.

[Michael W.]

Re: 3782870 Iron Alloy

I just checked a disassembled bare 3782870 block mid 1963. There was an 870 above a 721 cast into the front of the block to the left of the cam and crankshaft bores, and a G17 in the same location, to the right.

The 721 would indicate that the pattern would also be suitable for a 3790721 block

[John H.]

Re: 3782870 Iron Alloy

In the 60's, the Saginaw Grey Iron Foundry was pouring over 3,000 TONS of iron every day, a small part of which was 5,500 V-8 engine blocks, plus over 40,000 other castings which went to Flint V-8 every day. They also poured THOUSANDS of other castings every day for Detroit Gear & Axle and many other Detroit-area Chevrolet manufacturing plants.

I'd love to see the guy whose job it was to "grade" 300 raw-cast V-8 engine blocks every hour for specific applications (just being facetious - that didn't happen). Saginaw Grey Iron was the largest, and highest-volume iron foundry in North America in the 60's and 70's, and they didn't do "specials" in that kind of environment.

[Terry M.]

Re: 3782870 Iron Alloy

Guys, it was the 1980s before I got to go through Saginaw -- but when John talks high volume you have no idea what that means unless you have seen it. Even in the 1980s pallet loads of cylinder cases were going into semi trucks just as quick as the fork lift operators could get them in -- and there were a bunch of fork lifts. They ran in a precession ballet like operation that was remarkable to see. The expression a$$holes and elbows comes to mind. Checking or culling individual cases just didn't happen. Yes QC pulled a case now and then for testing -- sometimes destructive testing, where they cut the case apart to check for wall thickness and the like -- but to test for alloys? That was/is someone's pipe dream like mitting.

BTW: At the 3000 tons a day -- those furnaces NEVER were cooled off except for relining of the refectory brick. They were kept hot 24/7 because of the heat stresses that cooling would induce in the structure and the time it would take to cool and bring them back to temperature. Relining was a major undertaking as well and was scheduled some time (like a year) in advance.

BTW 2: I thought Saginaw Cast Metals now uses the lost foam process in addition to sand casting for aluminum production. Where is Mark Gorney when we need him?