Block ID and Plate Numbers

[BoldUlysses]

Hi guys. Need a second opinion on this. Here's the story:

When my '72 was repainted in the late '70s, the engine bay was (sadly) blacked out. In the process, the ID plate that lives on the pass. strut tower just above the voltage regulator was painted over (which explains why I hadn't noticed it before now).

Sunday night I removed it and scraped as much paint off it as I was willing to (will do the whole thing eventually). The block number stamped into it reads 110555:

The number on the block itself, however, is 118555:

I'd originally thought it was some kind of typo. My dad is the car's original owner, it's always been in the family, and he swears up and down the engine was never, ever replaced. The engine was rebuilt in the mid-'90s, but (according to my dad) not replaced.

A gentleman on another Z forum conjectured:

Looks to me like you have a mis-stamped service block.

The numbers don't have the familiar 'cursive' bent normally associated with Nissan OEM Stamps.

See the "L24"? the scripted numbers for the engine block should be similar, with the top section of the "8" looking somewhat like an Onion with the green chopped off if that makes any sense. Along with the bottom section of the "5" being a bit more "open" and not a "Reverse C" configuration.

I have never seen a mismatched plate/engine from Nissan, ever.

My surmise would be that you have a 'service block' which arrived with NO serial number in it, and generally the dealers left that blank when they installed it.

Looks like someone sometime got a letter-number stamp and just put the numbers on your block.

And they mucked it up.

Having a Service Block in with NO serial number arguably can be said to have a "Factory Service-Replacement Nissan Engine" and wouldn't necessarily be knocked down for not having an 'original' engine (some Z-Owners blew their 70's engines at Auto-X and got replacement engines from Nissan UNDER WARRANTY! What happened to THOSE days GT-R Tranny Owners?)

Unfortunately what you have is most definitely NOT "Matching Numbers" but if you had service history to show the swap/change you could argue the accident like you theorize.

Based on that, I have a couple theories as to what happened:

1. I wonder if the block was replaced when the engine was rebuilt in the mid-'90s, unbeknownst to my dad. The engine bay had long been blacked out by that point, so maybe the rebuilder had trouble reading the plate # and made an error applying the numbers to the block? Of course, all that would assume L24 "service blocks" were still available from Nissan in the mid-'90s and that the rebuilder had access to them.

2. My dad bought the car new, but what if the engine had been replaced before he drove it off the lot? Would that be a possibility? The dealership is long gone, so I can't exactly investigate that theory.

The "numbers matching" thing doesn't matter to me with respect to the car's value, but I would like to be aware of its history.

What do you guys think?

[73str86]

The error in self-stamping the block by some Datsun/Nissan mechanic is plausible I suppose. If one noticed the mistake, they likely would not have told anyone or...told their supervisor and figured the owner would never know the difference. How many people know the block number on their new(er) daily driver nowadays? Not I. Lastly, I suppose if this was your conclusion, so be it. It just seems like an odd thing to mention to someone. But I also see it likely that your father (or anyone else's) may have forgotten about a surprisingly large repair bill 20+ years ago.

I'm also trying to delve into the history of my '73 Z. The PO I bought mine from owned it for 36 years, bought it with around 40,000 miles from a Datsun dealership in VA. I keep trying to jog his memory of anything he has done to it. I have all the documentation, titles, warranty book, etc. My block matches my plate number. But is also has '72 four screw carbs, a header, four point roll bar, chrome rims, and a rear sway bar. Besides normal repairs and maintenance, PO swears the only thing he ever did was have the "crap-shot flat-tops" replaced with earlier versions and install aftermarket mirrors.

Either way, it's fun to learn about the history of our cars. It's nice to hear yours is staying in the family.

[BoldUlysses]

The error in self-stamping the block by some Datsun/Nissan mechanic is plausible I suppose. If one noticed the mistake, they likely would not have told anyone or...told their supervisor and figured the owner would never know the difference. How many people know the block number on their new(er) daily driver nowadays? Not I. Lastly, I suppose if this was your conclusion, so be it. It just seems like an odd thing to mention to someone. But I also see it likely that your father (or anyone else's) may have forgotten about a surprisingly large repair bill 20+ years ago.

I'm also trying to delve into the history of my '73 Z. The PO I bought mine from owned it for 36 years, bought it with around 40,000 miles from a Datsun dealership in VA. I keep trying to jog his memory of anything he has done to it. I have all the documentation, titles, warranty book, etc. My block matches my plate number. But is also has '72 four screw carbs, a header, four point roll bar, chrome rims, and a rear sway bar. Besides normal repairs and maintenance, PO swears the only thing he ever did was have the "crap-shot flat-tops" replaced with earlier versions and install aftermarket mirrors.

Either way, it's fun to learn about the history of our cars. It's nice to hear yours is staying in the family.

Thanks for the reply. Part of my motivation concerns my goal for the car. It needs a down-to-the-metal restoration, and the engine needs a rebuild (was run w/o oil pressure for several minutes years ago and hasn't been started since). If the engine is original, then I want to rebuild it for sentimental reasons. If it's not, then I can just replace it with a compression-tested L28 or some such. So a big part of my goals for the project are riding on whether or not the engine is original. Next step: Locating the shop that did the rebuild in the '90s and seeing if they have any records.

Cool about yours! I hope you're able to piece together its history. Correct me if I wrong, but weren't the earlier carbs the 4-screws (~'70/'71)? My '72 has 3-screws.

[BoldUlysses]

Found another piece of the puzzle. Alex commented on my blog post detailing the block ID / plate mismatch, and posted a link to his registry, wherein there's a long list of VINs and engine numbers.

Turns out, if you focus on the section where my VIN (93069) falls:

that the only plausible block number would be the one that's actually on the block, 118555.

What that means is that the number stamped from the factory on the shock tower ID plate (110555) is wrong. Pretty wild.