I'm looking at buying a '68 big block and I'm hoping to get some insight about the engine. The owner insists the engine is original to the car, but there is no documentation at all, and the block appears to have been decked: the stamp pad is as smooth as James Bond. Also, he says it's an L68, but the decal on the air cleaner says 435 hp, indicating that it should be an L71. However, the decal is in excellent condition, so it appears to have been replaced, and therefore wouldn't seem to be a reliable source of info. The tach looks original to me, and has a 5600 RPM redline, which I think means that the car left the factory with an L36 or L68, not an L71.

In addition, the block date code is A118 and the trim tag date code is I03 (the trim tag also looks to me like a reproduction). The vehicle build date of April 3, 1968 does correspond to what I would expect based on the VIN, but the block casting date of January 11 seems way too early for an April build date.

So my questions are: 1) Is it possible that an engine whose block was cast in early January would have been put in a car built in April? 2) Is there a way I can tell whether the engine is an L68, an L71, or an L36 that someone swapped to a 3x2 setup? 3) Are there any '68 big block owners here whose car was built at the end of March or beginning of April who would be willing to post their build date and block casting date? 4) Is there anything else I should look at that might help shed some light on the matter?

Also, for what it's worth, the transmission does appear to be original. The VIN matches and the date stamp is P8C26, which seems reasonable for an early April build.

Thanks.

 

1) It's possible but not probable that the engine sat on a rack for 3 months before being chosen for an installation. The majority of engines are cast and then assembled 1 to 4 weeks prior to the car assembly.

2) Look on the side of the block above the oil filter for 2 threaded and plugged bolt holes. (black and orange in this pic by J.Hinckley - the threaded hole above and right of the orange plug is for the clutch pivot) If present, it may indicate a 4-bolt mains, solid lifter block which the 435hp came with; if no plugs then it's a 2-bolt, hydraulic lifter block (L36/L68 if original to Corvette). The L-68 is an L-36 block with a changed intake - there is no difference in the assemblage of the block or heads.



3) I'm not sure this will tell you much.
4) Other than identifying the chassis as a big block vs small block installation, there's not much to identify what specific engine it came with.

The altered block pad and replaced trim tag are significant road blocks to finding out much about the car other than it's not reliably in its original configuration - there is zero value to what the owner says it is. Without stripping paint you don't even know what the original color should be. I'd treat this car as a "tribute" and not pay a premium for any sort of originality.

If you want to dig further, there should be date codes on the heads (under the valve covers) as well as the carbs. The heads should be within days or a couple weeks of the block. (Not sure about where the tri-power intake date is located.)

 

Welcome to the Corvette Forum 1994ZR-1!

You are in the right place to ask questions and get help with your Corvette. We are glad you have joined us here!

The only way to be absolutely certain would be to see the "Build Sheet" that was attached to the top of the fuel tank on the 1968 models. Sales records from the original sale would be great but so few were kept by the original owners. Using a flashlight and a mirror take a look over the top of the fuel tank and see if there is evidence that the sticker is still there. Mine was missing except the outer edges and provided no use to me.

First of all be very careful when buying a Corvette based on what a person tells you or the Engine Stamping numbers. Number stamping is now being done so routinely that it cannot be trusted anymore. Simply making any engine look "right" will bring lots more money when it is sold. A Tri-power Corvette is something that some people will pay extra for and that is likely the reason for the sticker on the air filter. My 1968 was delivered with the solid lifter 427 and it was missing the intake and carburetors when I bought it.

To know what the car is you would have to have a person very knowledgeable about the 1968 Model year and ALL of it peculiarities. The 1968 engine verification would be done by checking all the date codes on several vital parts. The NCRS might have some information that could help you identify the parts and identify what your C3 came equipped with.

 

Thanks for the info. How can you tell if the car shipped with a big block or small block? The only thing I know to look at is the half shafts, and they've been replaced.

 

Thanks for the reply, and for the welcome. I appreciate the info and insight you guys have provided.

 

BB = larger front spring diameter, larger front sway bar, and rear sway bar, and diff h/s yokes that have caps not u-bolts. And tach redline is engine specific. F41 option available on BB only.
Springs .600 or .605" coil dia SBC, .618 or .645 BBC, .680 F41
Fr Sway Bar: .875" SBC, .9375" BBC, rear bar BBC only, .5625"

 

Not specifically chassis details, but '65 to '69 rear axle gear ratio codes are small block / big block specific, as are the radiators and fan shrouds.

 

Thanks, everyone, for all the helpful information. It does have a rear sway bar, and the correct caps on the half shafts, although they've been replaced. Unfortunately, I'm not in a position to measure the springs, as the car is several hundred miles away. So far, though, it doesn't look like anything points to it having originally been a small block car, although I guess all of those things could be changed if someone wanted to make a small block car look like a big block car.

 

If it's like a 69, the L36 will have 2 fuel lines on the frame rail at the fuel pump. The L68/L71 would have a single fuel line.

 

Based on no stamp pad info and the questionable date difference between the build date and the block manufacturing date, as suggested above, I would not pay a premium for originality. Id also keep in mind these questions/issues will probably surface when you sell the vehicle.

 

I'm back, with a little more information, and a lot more confusion. The owner sent me some photos, and rather than clear things up, they have only confused me even more thoroughly than I was before. He said he couldn't get a photo of the casting number, but thought it looked like 8963512. I'm guessing he misread the first digit, and it's really 3963512, which would make it a 1969 block.


The block date code looks to me like A118 followed by a space and then a 9. If I'm reading it correctly then the block was cast January 11, 1968. I don't know what the 9 means. Is that the year, and I am misreading the beginning of the date code?

The head casting number looks like 3931063, which should be a 1969 L36 or L68, so that would match with the block casting number.

There is also what looks like a C4 and a 9 separated by a large space. Is this the date code?

In another location there is a PA followed by two digits that I can't make out. Both of them could be 3 or 8. Finally, there is a circle of 11 dots with a dial pointing to the seventh dot. I can't find anything about what the PA code or the dots mean.

Also, he sent me this photo of this mysterious information located on the block near the oil filter. Can anyone shed some light on it?


Based on the block casting number and the head number, it seems like the engine is out of a '69, but if I'm reading the block date code correctly that would be highly improbable. Maybe what I think is an 8 is really nothing, and the 9 is the year? If that's the case then it seems like everything might match and someone swapped out the original engine for one from a '69. If anyone can help unconfuse me, I'd sure appreciate it.

 

Thanks, 3X2 and pltmgr. That's helpful info.

 

1. The casting date for the block, I believe, is Jan. 11, 1969 and for the head it's March 4, 1969 (screw between the 4 and nine). Could the gap in the block casting date be a screw head?
2. What you are seeing with PAxx is merely an abbreviation of "Passenger" as opposed to "Truck", nothing more.
3. The 11 dots and pointer is the clock indicating what shift was working when it was cast.
4. I don't recall if the K on the side of the block indicates which casting pattern was used... but that may be what it is. If so, different blocks will have different letters just by the luck of the draw of which patterns were used when pouring the hundreds of blocks per day(edit below). I know the pattern sometimes appears on the top of the rear flange where the casting number is located. (Casting info locations changed over time.)

What the dates mean is that the parts had to have been cast a week or more prior to the car's VIN (birthday) which doesn't seem to be the case, being the car is a '68.

edit: reworded so as not to imply a single pattern produced all blocks on a given day

 

OK, so then it appears that this is a 1969 motor, and it's either an L68 or an L36 that someone swapped the intake manifold and carbs. Is that your opinion, based on the limited info I've provided?

 

Yes. It sounds like what you would call a "period correct" L36.
Not a born-with motor.

So what if it is still a nice car?
Just make sure you pay appropriately.
Unless you really want a numbers matching car, and are willing to pay.

Mine is far from numbers matching.
But is still a 500+HP LS6 engine, and should be a hoot to drive, and I don't want to worry about driving a high dollar collector car in today's traffic.

It's not always about the money.

It could be about the fun.

 

I have a higher resolution version of that photo, and it sure looks like A118 9 to me. Maybe that's just because I was expecting it to be an 8 and now I can't unsee it.

Thank you for your help. You and all the others have provided a lot of very helpful information, and I really appreciate it.

I like the car a lot, and the replacement motor isn't a dealbreaker for me. I'd prefer the car had the original engine, but then again, I'm not looking for a show car. I want something I can drive every day and enjoy for the rest of my life. I had a '68 convertible once, and I've regretted selling it every day. I don't intend to make that mistake again

 

Welcome to the forum and post some pictures of the car so we can see it!
If you’re not worried about having the original engine, then just make sure you are getting what you really want.
One thing I really wanted was an unmolested Corvette to start with.
My engine was originally a numbers matching big block car, but I swapped the original engine and TH400 transmission with a 496 and 5 speed manual.
Crawl up underneath and check really good for rust on the frame and birdcage because that is more of a deal breaker than any engine swap.
Look up under the dash and feel for any rust on top of the wiring, components and anywhere else you can get your fingers into.
Good luck and keep us posted!

 

Thanks, OldCarBum. The frame looks really good. I suspect it may have been sandblasted at some point, maybe when the car was repainted. I couldn't see any evidence of rust along the windshield header or the A-pillars, and I saw only a little minor surface rust at the front body mount points. It didn't occur to me to check up under the dash. Thanks for pointing that out. I'll see what I can find there when I go back.

 

Whats the price....if its 30 or below then its fine if its not a matching numbers block as long as he realizes its not. If he keeps insisting walk away unless its for sale in the low 20s then it really doesnt matter, buy it because a big block chrome bumper car in the low 20s is a good price. IF he3 wants anything over 30 your are losing money on a non original car if you are buying it for NCRS shows. Hows the paint and interior. WHat the engine and engine bay look like. Whats the rear ratio.

As to your original question there is 1 way to know how your car came from the factory as a big block car...you are the original owner. Everything else can be faked even the broach marks and stampings down to casting numbers.
If he has the build sheet that is a positive. If the block wasnt decked then thats good too for resale but again, people have faked those in the past.

 

I have no intention of showing the car; I'm looking for a driver, and I don't plan to ever sell it. This car has been restored and looks like it's been garaged since then. I don't think it would get very far with an NCRS judge, but it would draw a lot of oohs and ahs at a local show.

The car has been repainted and the paint is very good, as is the interior. The carpet has been replaced and looks brand new. The upholstery looks original, but I think its condition is too good, so it may have been replaced as well. The gauges all work, and so does the clock. The fiber optics do not. The frame looks very good, with some rust but nothing that I think would be concerning. Windshield header and A-pillars look good to me, and there is only a little surface rust behind the kick panels. The engine bay is also very clean. The alternator, distributor, and wiper motor are all new. So are the brake master cylinder, power brake booster, calipers, and rotors. All signs point to the engine being a replacement out of a '69. The transmission looks original to the car, with the correct case stamp, date stamp, and VIN. Half shafts are new, and all the suspension bushings, front and rear, have been replaced. The car also has the aux hard top, a new soft top, and new weatherstripping all around. It also has power windows, for what that's worth.

$30K seems very low to me, even with the replacement motor. This one that sold on BaT a few weeks ago is nearly identical:

https://bringatrailer.com/listing/19...onvertible-55/

From the pictures it doesn't look to be in any better condition inside or out than the one I'm looking at, and the block stamp pad has obviously been altered. There wasn't enough evidence to prove one way or the other whether the engine was original to the car, and it still sold for $60K. That's far more than I'm willing to pay, but $30K still seems very low.