Zed Head

This was a clue that it was an electrical problem. If the engine was still spinning because it was in gear then spark will still move the tachometer needle.

Another VRP car. Already sold once for $101,240. https://bringatrailer.com/listing/1972-datsun-240z-380/ https://bringatrailer.com/listing/1972-datsun-240z-93/

Should have put it on BaT so we could pick it apart!

It looks bent around the exhaust pipe. Maybe backed the pipe in to something and it caused some damage. Good Not so good, but not terrible. The bumper looks a bit dinged up on the bottom too.

I'd see if you can work out a deal for the proper head if you're looking to be close to a restoration. I don't want to hurt zKars' position but he did say "never been able to sell". Seems like he's been waiting for you... Good luck. I redid the math for what should be the E31 head and got 7.7. Didn't add your millimeter overbore though. Also found that some of the engine calculators out on the internet seem to have the wrong chamber volumes. I used the dimensions and reported CR from the FSM to calculate volume. Just for fun.

Is there a specific reason that you're trying to save the L20?

I got 7.5 for the CR of an L24 head on an L20 block, assuming the L24 head is the dual SU head. Probably want to get with zKars on that L20 head. Realized that I used the E88 L24 head for the calculations. 8.6 CR instead of 9.0. I'll redo them later. Probably still under 8 CR.

Disconnect at the manifold/header exit and run your borescope up that way. That distributor looks like just a magnetic pickup distributor, that uses an external ignition module. But your exhaust blockage sounds reasonable. Good luck. Post pictures.

I ruined a GM HEI module by running the engine with two spark plugs disconnected. I assume that a stray high voltage discharge, or some sort of "flyback" (it's a thing), made its way through the module. After I turned the engine off and reconnected the wires the engine wouldn't start. I checked spark and got a weak orange spark. The engine would start with starting fluid but would not without. Put a spare new module in and it fired right up. How about some details, just for fun, on the new electronic? Is it a ZX type or Pertronix or something else?

I've also seen old plug wires crossfire or short to ground. Waaayyy back in high school working with old worn out car parts. Used to have to arrange the wires to avoid problems. Also seen that visible weak spark does not always spark under cylinder pressures. Had a weak ignition module once. You're probably running points though?

You can back out combustion chamber volume using compression ratio and displacement. The 1972 FSM has the numbers. And if you have the head and block in hand you can take some measurements.

How about the old standard of mixed up firing order? Just watched a pro do that. It happens.

I think that I saw that or something similar on PBS or one of those channels. It was more focused on the main guy with the mustache. Rick Hall. Pretty fascinating show. https://en.wikipedia.org/wiki/Rick_Hall

Here's a nice No Reserve 72. Already up to $25K. https://bringatrailer.com/listing/1972-datsun-240z-379/

Here's one of those weird songs you might have heard once or twice but never knew who played it. Interesting story behind the band.

BOT!

Before you get too far you might as well find the ECU. The brain box. It's over by the driver's left leg, behind the kick panel. It controls the injectors. Unless you're planning to run carbs.

One of them is incorrect for the diff then. That's just the way they were built. You can see it in the eBay picture and in the illustrations. One is longer than the other. That's why you get the same result when you swap them. Because yours are the same length when they shouldn't be. If you bought the diff used it might be that the seller popped the axles out for storage and gave you a mismatched set by accident. I used to have several R200's and I stored them with the axles removed sometimes. Anyway, in short...your stub axles should be of two lengths, not one. Good luck.

The seller says it was put back to original color. The pictures of when it was red show green on the firewall and the floor. Overall, in the comments, there is much enthusing over a pile of parts. A shiny paint job will do that.

Pictures would help. When you say yoke do you mean flange? And when you say yoke again do you mean "stub axle"? Nissan calls them flange assemblies, most people call them stub axles. The original axles are of different lengths, side to side. Sounds like you're rebuilder might have put a long one where a short belongs. Notice the different part numbers from the carpartsmanual. https://ebay.us/m/jAyp3m Datsun Z Differential Gear, Pinion & Cover (R200)

Perfectly? That seems unlikely. It's odd enough that a British thread pitch would be used on a Japanense car in the late 60's/early 70's. Why would British be used on the block and US on the balance tube? Chaos! Your thread chaser might cut some new threads though. People have used NPT in the oil pressure sender hole and made it work. Soft metal will distort.

Here's a puzzle for somebody. Comes with a car cover. No reserve. https://bringatrailer.com/listing/1971-datsun-240z-330/

Read the articles here about the GM HEI module, if you find that your wiring is smoked or the factory Transistorized Ignition Unit (TIU), aka ignition module, is gone. You can run wires in the engine bay directly from that terminal block with the green and red wires. https://www.classiczcars.com/articles/electrical/

Is BSPT a possibility? The prevailing internet Z forums' "wisdom" is that the oil pressure sending unit holes are BSPT. JIS VS BSP: What's the different ?Before choosing a suitable thread standard, it is necessary to understand from various aspects. This article will introduce the difference between JIS and BSP, so that you can better choose the thread

Sounds like you're saying things have been just fine then something changed. As opposed to the brakes having always bothered you. If it was mine I'd find the source of the sudden problem before "upgrading" anything. Otherwise you could add the upgrades and end up with the same problem, never solved.