You've seen and heard it before: "Numbers matching". Usually
there's a hefty price tag associated with those numbers as well. A
true "numbers-matching" muscle car is always worth more than one
with unoriginal drivetrain parts, so the question is, how do you
determine what is and is not matching numbers? It's really not that
difficult, you simply need to know where to look and how to read
what you find.
In a nutshell, matching numbers refers to the
various codes and dates found on all the major driveline components.
These include the engine, transmission and rear-axle assembly. The
engine components themselves (block, heads and intake) will have
various casting numbers, date codes, and an engine identification
code, all of which are important and should be correct if the car is
to be considered numbers matching. In the next few paragraphs, we're
going to tell you where to find the various codes that matter for
the engine.
But first, let's give
you a little background on why the numbers are there. The date code
and casting numbers are mainly for identification and
quality-control purposes. Through the casting date, the day/night
shift indicator and, on some components, the "clock" position, it's
possible for Chevrolet to pinpoint within an hour or so when a
specific component was cast. Casting numbers also identify specific
"families" of components.
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For example, cylinder heads with the same casting numbers
will have similar applications, although some of the finishing
details, like valve sizes, may vary. Date codes are found on the
block, heads and intake manifold (along with many other areas and
components throughout the car, but for the purposes of our
discussion here, we're not concerned with those). Casting numbers
are also found on the block, heads, and intake manifold. Again,
other components carry casting numbers, some within the engine
itself, but we're concerned only with those that can be seen without
major disassembly.
Another important set of numbers is the
engine plant code/engine ID number. These were stamped on the engine
at the assembly plant (the engine assembly plant, not the car
assembly plant), and identified the date of assembly, which
particular displacement/horsepower combination the assembly is and
what chassis it was to be installed in. Additionally, after the
engine was earmarked for installation into a specific car, an engine
V.I.N. was stamped into the block by the final assembly plant. The
number included a division identifier (1 = Chevrolet), the last
digit of the year model, a code for the final assembly plant and the
last six digits of the chassis serial number (the sequence number).
The engine V.I.N. was included mainly as a theft deterrent (it's a
means of linking a particular engine to a car in the case of theft).
These numbers may not be found on early (pre-'65) engines.
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