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Old 12-06-2022, 01:06 PM
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Default Physical modifications in castings

It has often been asked - "why is the physical appearance of castings different in certain areas, when the part number is the same?". This phenomenon can even be observed in castings produced the same day. To explain the reason for this - let's start with how the 010 block is cast.

First, the V8 blocks at Tonawanda were cast on mold line #2 at a rate of 240 blocks per hour (maximum - actual production was about 190 blocks per hour considering downtime, pattern changes, etc.). So, in a typical production day (2 - 8 hour shifts) roughly 3,000 blocks were cast on line 2. Mold line #1 also produced blocks, but those were all MIV castings.

Each V8 SB casting took 9 cores to form the interior and re-entrant areas. These cores were "set" into green sand molds (compressed sand bound together with bentonite clay and water). So, the core department had to send roughly 27,000 cores via overhead conveyor to molding line #2 each production day. The required number of each type of core could not be produced on a single core machine, or from a single core box. So, multiple machines and multiple core boxes were used for every core.

So, why would one core box or pattern differ slightly from another of the same part? It may be hard to imagine in today's precision world, but back in the 60s and 70s the pattern shop (where the patterns and core boxes were made, repaired, and modified) produced new equipment on Bridgeport duplicators (later Ramboudi CNC machines replaced them) using a "master" pattern which was "duplicated" onto metal blanks that would become production equipment. Since all patterns and core boxes were produced off of the same masters - the multiple pieces of production equipment were all initially close to the same when a new part was introduced.

Then, production happened. Over years of use, individual patterns and core boxes were modified - mostly for casting quality reasons, but also after equipment was damaged in production. These changes DID NOT require Chevrolet engineering approval. When the foundry or the motor plant wanted to make a change, individual pieces of equipment were modified and sample castings were produced. These samples were specially marked so that they wouldn't be used in production without approval, and taken to the motor plant for QC approval before being fully machined to make sure that there were no interferences or objections. After successful trials, the changes would be approved for production. Chevrolet engineering was never made aware of the changes, and the pattern masters were not changed (that would have required Chevrolet engineering approval). Careful records were kept by the Master Mechanic (pattern shop) of these changes. After approval, the revised equipment was released for production and the castings produced were once again carefully monitored for production/interference issues. The final step was full approval of the modification, however - during the production run, the modification may or may not have been determined to solve the issue that precipitated the change. If the trial did not yield significant advantages - all of the equipment would not be modified. But, since the modification was approved - the trial equipment did not have to be restored to its original configuration.

More to come...

Last edited by bergy; 12-06-2022 at 01:14 PM.
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Old 12-06-2022, 02:29 PM
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Great stuff from someone who was there!

Any idea why there were two casting numbers for the same block? The production ZL-1 block had two numbers; no differences noted. One of the earliest cars had an 053 block.
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Old 12-06-2022, 02:47 PM
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Thanx for the education Bergy.....just wanted to express my recognition of your efforts and rich historical contribution to our hobby!!!!
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Old 12-06-2022, 03:46 PM
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Can't answer your question William - wish I could. My only involvement with aluminum castings was to help round up cores to ship out to Lockport or Winters. Only Chevrolet engineering could make part number changes, so there had to be a good reason. At such low volume, perhaps one pattern went to Lockport and slightly later version to Winters? Engineering required a foundry mark on castings to trace back the source. Maybe somewhere there is a Lockport or Winters logo on the castings? Since Chevrolet engineering made the change, it could have been just a subtle increase in wall thickness to improve strength in a critical area - just guessing.
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Old 12-06-2022, 04:43 PM
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Quote:
Originally Posted by William View Post
Great stuff from someone who was there!

Any idea why there were two casting numbers for the same block? The production ZL-1 block had two numbers; no differences noted. One of the earliest cars had an 053 block.
Maybe one was intended to be the casting number, and the other was some up-level assembly number?

K
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Old 12-06-2022, 06:20 PM
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Bergy - Thank you for your personal experience and insight into the foundry operation...awesome info!

Aside from the casting core variations, could you comment on M-coded blocks, (instead of the traditional casting date). Specifically, what types of changes would dictate creating M-coded blocks and typically how many were run for evaluation? I've been fortunate (unfortunate??) to have had two M-coded 010 blocks...one in a 70 Z28 and one in a '72 Z28.
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Old 12-06-2022, 06:45 PM
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Tonawanda did supply some 010 blocks to the Flint motor plant for machining into 302 and HP 350 engines, but only when the Saginaw gray iron foundry couldn't keep up with production demands. The blocks from either source were interchangeable, but proximity to the engine plants dictated the preferred casting supplier. Any "special" changes that I alluded to earlier were marked with a character to identify the casting as special. I frequently used a "X" that was pressed into the sand mold of the casting. Since the inspectors in the foundry finishing department had to check the castings for a complete date code - it was convenient to put the special "mark" near the date code so that the inspectors would notice it & specials could be set aside & not mixed with regular production. Not sure what was special about your "M" coded blocks. We used an "X" every time a special was run - so it didn't always designate the same special feature. The "X" code along with the specific date could be traced back to the specifics of the special.
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Old 12-06-2022, 07:08 PM
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Default casting changes

OK - rainy day here & I just got off the phone with Mark B. Mark asked some questions about the foundry molding process, so I figured it best to post some info for the community. Conveniently, I had the pattern shop make up a gift for Jim McLernon (GM of all Chevrolet manufacturing) that I gave to him when he visited our plant. when I left Chevrolet - the plant gave me the same gift (a miniature cylinder block) along with the molds that it took to produce it. I dug them out & can use them for illustration.

First - the top (cope) and bottom (drag) halves of the molds were produced in "green" sand (silica sand bound together with bentonite clay & water). A container (flask) was placed over the pattern, and sand was automatically dumped on top of the pattern/flask assembly. Next, hydraulic squeeze heads compressed the sand/clay mixture against the pattern. When the flask was lifted off of the pattern, it contained a perfect impression of the pattern in the sand/clay material. Using my miniature parts - here's what the bottom mold and some of the cores that had to be set into the mold looked like:
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Old 12-06-2022, 07:11 PM
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Default casting changes

Next, the cores that formed the interior & re-entrant parts of the casting were set into the lower mold. Not all of the cores are shown here, but you can see the front & rear housings along with the barrel cores.
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Old 12-06-2022, 07:17 PM
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Default casting changes

Finally, the mold was closed by setting the top half flask (with the green sand impression of the top of the casting) onto the lower half of the mold (with cores in place).

Then - the completed mold traveled on a conveyor to the metal pouring station where the mold was filled with molten iron at roughly 2600 degrees F.

After shake out, blast cleaning, and grinding - that block looked like this
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