Can this 1970 LS-5 block casting date be original to the car?

[Mark E.]

but by no more than six months" (page 92).

Numbers and history:

VIN: 194370s412931
Certification label on door jam: 194370s412931 R 6-70 (June 1970)
Body build date from trim plate: F22 (June 22)
Engine pad: 70S412931 T0608CZU (Suggests engine assembly on June 8, 1970)
Cyl head casting # & dates: 3964290 D1570 (both) (April 15, 1970)
Intake manifold casting # & date: 3855287 E870 (May 8, 1970)
Engine block casting # & date: 3963512 H259 (August 25, 1969)


I purchased the car in January 1990 from a local north Texas car dealer for $14,000. The odometer showed 97,000 miles and it was all there, mostly original, but worn- I'd say a mediocre #3 car. It looked like it was treated as a fun driver for 20 years- mechanically maintained but cosmetically tired. Like many transactions with dealers, it came with virtually no documentation. DMV records show three previous owners since 1977; no luck going further back.

After I bought it, I spoke with the previous owner. He bought it for $7,000, kept it for three years and sold it to the dealer I bought it from for $9,000 (remember, this was in the late 80s). During that time he said he overhauled the engine himself because of oil consumption. Nothing extensive: hone, new timing chain, oil pump, cam, lifters and rings, valve job, while using original pistons, rockers and push rods. He said it looked like the engine hadn't been out of the car before.

[Mike E.]

Re: Can this 1970 LS-5 block casting date be original to the car?

It's possible. Pictures of the stampings on the pad would certainly help. The gap is at least before assembly. After would absolutely be out of the question.

[Mark E.]

Re: Can this 1970 LS-5 block casting date be original to the car?

Here's four shots of the engine pad. Maybe this is better looked at in person?

Engine Stamp 1.jpgEngine Stamp 9.jpgEngine Stamp 11.jpgEngine Stamp 5.jpg

[Patrick B.]

Re: Can this 1970 LS-5 block casting date be original to the car?

I think this looks pretty original.

[Mark E.]

Re: Can this 1970 LS-5 block casting date be original to the car?

Thanks Patrick. If this is original, what would explain the early block casting date?

Could one possibility be that the block initially failed a quality check? From page 55 of the Judging Guide: "All engines were subject to a number of quality control checks... If an engine assembly failed... it was disassembled in the heavy repair area. On these engines,... the time span between cylinder case casting date, stamped engine assembly date, and vehicle build date exceeds the norm."

Have other reasons been documented?

[Patrick H.]

Re: Can this 1970 LS-5 block casting date be original to the car?

I think this looks pretty original.

You think those are factory grind-out marks under the VIN?
That's what crossed my mind.

[Patrick B.]

Re: Can this 1970 LS-5 block casting date be original to the car?

Thanks Patrick. If this is original, what would explain the early block casting date?

Could one possibility be that the block initially failed a quality check? From page 55 of the Judging Guide: "All engines were subject to a number of quality control checks... If an engine assembly failed... it was disassembled in the heavy repair area. On these engines,... the time span between cylinder case casting date, stamped engine assembly date, and vehicle build date exceeds the norm."

Have other reasons been documented?

I have a 427 390 1966 Passenger car block cast in Dec 65 and built May 66. I don't think anything unusual happened to it at Tonawanda. I have seen other blocks that had been stamped at Tonawanda twice, months apart. I think those were engines that failed some test and were then disassembled and the block re-used without grinding off the first stamping. The six month rule is a NCRS guideline not a Tonawanda policy. I would be much more surprised to see a Flint smallblock with a 6 month span than a big block with a 9 month span. Yours is just an oddball.

[Mark E.]

[Jimmy G.]

Re: Can this 1970 LS-5 block casting date be original to the car?

My opinion It looks like a factory rework engine so the possibility exist that it is original for the car

[Michael W.]

Re: Can this 1970 LS-5 block casting date be original to the car?

From the pics it seems one/both stampings have been ground out and redone. Unfortunately the VIN section of the pad seems to have been rubbed or polished perhaps in a recent effort to make it legible.

Is your concern how this engine would be assessed in Flight Judging, or more trying to determine if it's the factory original?

[Patrick H.]

Re: Can this 1970 LS-5 block casting date be original to the car?

Please note that I'm at work, and don't have good photo editing software here. So, the attached pics don't look as good as I would like.

Here is what I see -

There is evidence of normal broach marks above the VIN derivative. I highlighted those.
There is a rectangular "box" of marks under the VIN stamping which shows evidence of having been ground down. I have tried to highlight the box in the photo, and note how the marks underneath are perpendicular to the original longitudinal marks I highlighted.

There is evidence of similar grind out under the assembly code, as well as evidence of former letters and numbers. I have tried to highlight the grind marks under the current code as well as a few remnants of former letters.

Given that the stamps both look correct, I wonder if the block went back to Tonawanda for rework, or if it was so unlucky that it got reworked once at Tonawanda and once at St. Louis.

Having said all that, the current stamps are, I believe, evidence that it eventually made it into this car on Day 1 and has been there since that time.

Patrick

[Mark E.]

Re: Can this 1970 LS-5 block casting date be original to the car?

Jimmy, Michael, Patrick- Thank you all for your time and expertise. I appreciate the help and am impressed with the level of support shown on this forum.

Michael- Since purchased 20 years ago, I've put a lot of my time and a bit of $ to bring the car to a strong #2 that I can occasionally enjoy on the road. When purchased in 1990, it was mostly original but worn. I bought it because I love the 70-72 vintage and wanted a high option 454, 4 speed, AC car. This car also has deluxe interior, PS, tilt, stereo, PW, alarm... just about every option but PB (go figure that one) and rear defrost. It has a good set of numbers also... correct (and I believe original) components include the engine and related castings (we think- as discussed here!), transmission, rear end, carb, compressor, distributor, etc. The original alternator is long gone and presently the car sports a nice looking Rockauto.com lifetime alternator ($35!) with an incorrect GM casting. I replaced or had repaired the dash, engine, and AC harnesses to original condition (when I bought the car, the dome lights came on when the clutch was pushed in!). I replaced most of the interior (seat covers, console, door panels, carpet- all just worn out) and much of the exterior trim, rebuilt the front and rear suspension, repainted it in its original Donnybrooke Green (with lacquer in my garage- that's a story to tell). The LF fender was apparently replaced in its past and it has replacement front grills (exposed screws), but the remainder of the body plus the frame looked virgin. The chassis/frame is dry except for the windshield frame (which I had a professional metal man repair), and the core support which I replaced. Mechanically it's stock except for the rear spring (installed a fiberglass unit to improve ride; I have the original), plug wires (Taylor 8mm braided- looks stock to the casual eye), tires (215/70-15 radials) and a tuner carb (running a 7040505 NA9 I bought that's jetted and tuned to run nice; I have the original 7040205 in a box).

So to answer your question, even though the car is set up as a nice driver, I want to know if the engine is original. I'm not an NCRS judge, but maybe it could achieve flight (3rd?, 2nd?) by putting the original bits back on, and installing reproduction tires/belts/hoses. But who knows? It has a lot of reproduction interior and trim parts so it may not do so well.

In any case, it's a nice looking Corvette and you can probably tell I'm proud of it.

Thanks again.

[Mark E.]

Re: Can this 1970 LS-5 block casting date be original to the car?

Jimmy and Patrick-

Thank you so much for your insights! What a great forum- where else can a guy get expertise like this by just asking?

After searching this forum and Corvetteforum.com it looks like there are several examples of unusual casting and stamping date combinations in 1969, 1970, 1971. Maybe the numerous strikes in that period caused some havoc with production and inventory control? Plus I don't believe GM was known to have the leanest production and inventory control practices to begin with. Six to 10 months of WIP sounds like a lot, but this might not have been uncommon.

Is there a write up of the rework/scrap processes for Corvette production, how this caused stuff to be routed between St. Louis and its feeder factories, and the resulting WIP cycle times? This might help us appreciate what date combinations are possible.

[Patrick B.]

Re: Can this 1970 LS-5 block casting date be original to the car?

I could not tell from your pad photos whether any former stampings had been ground off. If so, it should be very easy to detect them with a small steel ruler as a straight edge. I would expect the grinding depressions to be .020 to .030 inch deep, almost as much as a spark plug gap.

[Patrick H.]

Re: Can this 1970 LS-5 block casting date be original to the car?

Mark,

Any chance of a higher quality/resolution photo?
You could email it and I could try and highlight some of what I was describing.

Patrick