1970 Big Block date code

[vetteboy86]

I'm looking at a 70 BB coupe 4sp. All the numbers check out. It is a very early production, first 300 built that year. Before I spend the money, worrying about a potential re stamp, I'm curious what date of manufacturer for the engine is expected for this car.

 

[Vettehead Mikey]

Obviously dated before the car was completed, typically two-ish weeks. Worry equally about it being a bogus big block with a good restamped pad done somebody who knows what he's doing. I'd have an experienced inspector with good credentials inspect the car if you're paying 'original engine' money for the car.

 

[6880 Mike]

Block casting date could be mid December 1969 or a little later. Engine assembly date on the block pad should be within a couple of weeks of the time/build code of the car.

The original engine would have been assembled at Tonawanda, New York; stamped with the assembly date; then shipped to St. Louis where it would have been on hand before assembly of your Corvette began.

 

[vetteboy86]

The casting number checks out, but that particular casting number was used for 1969 as well I believe. Also, there is a 3 digit suffix on the stamp pad that matches.

Where is the best source for decoding these blocks, a complete listing would be ideal, but I imagine I would be hard pressed to find that.

Thanks for the responses.

 

[Tom Bryant]

You don't have a lot of choices for big blocks in 1970. Only the 454/390 was available in auto or 4 speed. The other option that changed the suffix code was transistor ignition.

Here are the 4 possible suffix code you could find on the stamp pad:

GZU- 4 speed
CGW- THM
CRI- 4 speed with T/I
CRJ- THM with T/I

All had Rochester carbs and hyd lifters. You should also find a VIN derivative stamped on the pad that matches your car's VIN.

With the 3963512 casting number block being used for '69 and '70 you have to go to the casing date to determiine if it's right for your car. The casting date is located on the top of the bell housing flange to the right of the distributor (apposite side of the casting number).

If you would care to post the stamp pad info and the casing number info we could tell if it's right for your car.

Tom

 

[vetteboy86]

The casting number is correct. I'm still trying to get date code information. How does the date code work?

The stamp pad suffix is CZU, there is some other information as well. I'm trying to get all the pieces to the puzzle before I make the trip to look at the car.

 

[Vettehead Mikey]

The casting date code will be alphanumeric, starting with a letter to designate the month: A=January, a digit or two digits for the day of the month then a digit for the year.

B219= Feb 21, 1969

In the stamped assembly code on the front pad, it's T for Tonawanda, then four digits for month and day (no year) then the engine suffix.

T0313xxx would be March 13th.

Post a pic of the pad if you can to at least weed out a timewaster restamp.

 

[vetteboy86]

Does the date code on the stamp pad match the location on the top of the bell housing? On the assembly line, was only the serial number stamped into the pad?

 

[Vettehead Mikey]

The casting date is on the top face at the rear of the block, the stamp pad is at the front of the block. Both are on the passenger side.

Only the engine machine code was stamped at Tonawanda, the VIN derivative was added at St.Louis.

 

[6880 Mike]

CZU identifies a 390hp 454 configured for a 4 speed transmission.
The four numeric characters preceding the CZU are the date the engine was assembled at Tonawanda (first two are month, second two are day of month).

The engine assembly date on the block pad must be earlier than the time/build date on the trim tag.

The Corvette Black Book, The NCRS 1970 Technical Information Manual, and Dr. Dobbins' book would be of help to you.

 

[JohnZ]

Does the date code on the stamp pad match the location on the top of the bell housing?

Nope. The raised date on the bellhousing flange on the block is the date the block was CAST. The engine assembly date stamped on the front pad could be a day later, or a month or two later.