[bergy]

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...