Page 41 of 68-82 Corvette Restoration Parts by Zip Products

zip resto tip understanding numbers codes nearly all of the major parts found in 1968-82 corvettes contain a part number and date code developing a better understanding of these numbers and codes and how they relate to one another will enhance your enjoyment of the hobby the logical starting point for the analysis of part numbers and date codes on any corvette is the car s vehicle identification number vin for all vintage corvettes the first several characters of the vin indicate the model year body style and assembly plant and the latter characters are the sequential number of each particular vehicle beginning in 1972 the fifth character in the vin indicated which engine the car originally came with the vin was stamped into a rectangular metal plate that was riveted to the windshield support frame at the driver side base of the windshield on all 1969-82 corvettes every car s vin was also stamped into the chassis in at least one place for most c3s it was stamped into the chassis on top of the side rail on the driver side in both the area beneath the door and the area above the rear wheel for all c3s the latter half of the vin often called the vin derivative was stamped into the car s original engine block this stamping was on a flat pad just above the water pump mount area on the passenger side it also was stamped into the car s original transmission case one way to help verify whether a specific engine or transmission is original to a given car is to compare the car s vin to the vin derivative in the stamping on the block or case a stamping that does not match the car s vin almost certainly means the engine or transmission is not original to that car a stamping that does match the latter half of the vin usually means the assemblies are original but even matching numbers does not guarantee this because of a practice commonly referred to as re-stamping in order to make a non-original engine or transmission appear like the original some people will stamp the correct numbers into the parts they accomplish this by either machining the existing numbers off or starting with a block or case that never had numbers stamped in to begin with evaluating the originality of engine and transmission stampings is a science unto itself and if matching numbers are important to you it is best to enlist the services of an expert in addition to the vin derivative original corvette engines also have what s called an assembly sequence this is stamped into the block adjacent to the vin sequence the assembly sequence indicates the engine s manufacturing plant date of assembly horsepower and application as with the vin derivative stamping the engine assembly stamping can go a long way in helping you determine whether a given engine is original to a particular car but as with the vin stamping engine assembly stampings can be re-stamped so just having the correct letters and numbers does not guarantee that the engine is in fact original production records for all corvettes built in the bowling green assembly plant still exist but precise assembly dates for c3s assembled in the st louis plant are not known you can however determine their approximate assembly day with a fair degree of accuracy for nearly all months of production the final serial number car assembled on the last working day of the month is known and therefore the total production for each month is known using this information and your car s vin you can determine which day your car was built for example if the final vin for february was 11,000 and the final vin for march was 12,600 and your car is vin 11,786 then you know your car was made in march you also know they made 1,600 cars in march divide that number by the total number of working days in the month and you have approximately how many cars were produced each working day and the vin range for each of those days plug your vin in and you know which day your car was made ­ give or take a day or two for slight irregularities in daily output once you have the assembly date for you car in-hand you can evaluate the correctness of all of its dated components all component manufacturing dates have to precede the final assembly of the car and the generally accepted rule of thumb is that they should not precede it by more than 6 months for example if your car was assembled on may 8th all of its dated components such as the alternator radiator wheels engine differential transmission and body glass will be dated earlier than may 8th but no later than about november 8th of the previous year if in fact those components are original reading manufacturing dates on most components is pretty straightforward typically a single number represents the year a letter represents the month with a being january b being february and so on and one or two additional numbers represent the day for example an alternator dated 9b21 was made february 9 1969 in addition to reading date codes it is also important to evaluate the part numbers on major components all major cast parts including the engine block cylinder heads intake and exhaust manifolds and transmission case have a casting number most other significant parts such as the radiator alternator starter distributor carburetor and wheels have either a stamped-in part number or a part number tag zip is open saturdays 10:00 a.m to 3:00 p.m est engine 39

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