Zed Head

Looks like you're getting it figured out. How did he evaluate wipe pattern if the retainers were interfering with the rocker arms? Maybe he centered the lobes on the pads at a certain rotation point and didn't actually see the whole wipe. Or he checked it with the interfering parts and didn't realize. Not clear. Just seems odd that he missed the interference between the parts.

This is interesting. How deep did he go? This would also change chamber volume. Considering the variation and the odd logic it might actually be worthwhile to remove the head and take a close look at what's been done. Trying to grasp sinking the valve seats to deal with "archaic design". Esthetics, function, machining problems? Curious about what he was trying to fix.

Just an observation, but I'd guess that any 80's era ECU of any brand would have those types of parts inside. If you have a local wrecking yard and get tired of waiting. I don't think that electronics were as varied back then, they probably came from the same supplier. You probably know that. Looks like a fun project.

Low number 1970. 5201. Interesting blend of old crustiness, new paint, new parts and lack of critical information. Not sure what to make of it. No engine number mentioned or shown so can't tell if it's matching numbers. Wonder how it will do. https://bringatrailer.com/listing/1970-datsun-240z-123/#comments

I see "taking things apart" but not the corrective actions to be applied. Trying to help formulate a plan of action. Assessing the wipe pattern before going further will tell a lot. Might be that many of the others are actually off the edge but just not too noisy yet.

Might be just me Edit _ I see Diseazd suggested starting with patterns. So not just me. Anyway, more observing and measuring seems in order ...but I'd do the wipe pattern before doing anything else. If all of the patterns are good except the last one then you know you have a one valve problem. What can you fix on the other eleven if lash and pattern are good? Besides that you meed a starting point. The wipe pattern gives you that, telling you if you need taller or shorter pads. Might be a simpler problem than it seems. Good luck.

So, summarizing the state of current affairs, is there a problem besides the

I meant in your driving video. But, apparently that's the right number. Assuming that the distributor is the original. The FSM does not say anything about removing the hose though. That is definitely a US domestic old car thing. I'm not sure how Nissan did theirs. They don't say.

It's not a tooth, it's the hole that the locating pin uses. But what really matters is the location of the notch relative to the groove, at TDC. The locating hole - 1, 2, or 3 - is used to get the notch in the right place.

Is the vacuum advance mechanism connected? It's not an emissions thing. Not sure what you're saying. 17 is a lot of initial advance if the vaccum advance is connected. You didn't say if the notch and groove picture is taken at TDC. Actually you haven't really confirmed the things that were discussed earlier about the damper pulley and the marks. It would help to confirm TDC and the damper pulley zero mark and the notch and groove and the cam sprocket position. 1, 2, or 3. You said earlier that you moved it from the #1 position.

Sounds lean. I would do whatever is possible to make it run richer. I don't know SU's.

Might as well check the condenser before you get too far along. It should have "OL" from the wire to the condenser body metal. No continuity. You can also measure capacitance if you have the right meter but it's not commonly done. And .020 is your point gap. It should determine the dwell on a new cam but a dwell measurement is more precise. It's measured in degrees with a dwell meter. As the cam wears the dwell could change. Mechanical ignition systems are more complex than they seem. Kind of amazing that they work like they do at high RPM. Here's a pretty good article from Pertronix. https://pertronixbrands.com/blogs/product-higlights/understanding-ignition-dwell?srsltid=AfmBOooVjLx4762Zc7UGTaiEOiTUuhwututQ4aKVsDB2ZJPHPywx_gMZ

Here's an experiment you could try if you just want to mess around and try things. It fits my earlier comment about too much current maybe screwing up the tach function (even though many people have done the conversion with no problems). Run a parallel power wire to the coil. This will reduce current through the tach sensor loop. You can run a jumper, then if it works, just run a permanent bypass wire. Overall though, considering cgsheen's comment about all of the people he knows with no problems, it might just be that the tach components are wearing out. There are many posts about flakey (flaky?) tachs. My 76 tach flaked out in the first few years after I brought the car back to life. It also had problems after the GM HEI module conversion even though it was already designed for electronic ignition. Electronics components weren't as high volume and consistent in quality in the 70's as they are today. Today's light bulbs have printed circuit boards inside. It's crazy. Anywyay, this shouldn't hurt anything. Not sure why that red line came out pink. p.s. you can just run a wire directly from the battery terminal for the test. The engine will keep running though until you remove it. Hot wire.

The modules work the same way. It could be a permanent change.

You don't like the four lug wheel options?

It can still be difficult if you have a dash cap. The cap holes are barely big enough. The 260Z and 280Z tachs are voltage driven. They'd work but you'd need to rewire them with a wire from the negative post of the coil. Probably with the 2.2 kohm resistor. And you'd need to connect the power wires when you remove the 240Z tach since igntion power runs through it. Not a big deal really. And, the fonts are different. A new thought - it might also be that the matchbox module is failing. Is it Nissan original or aftermarket? You could wire in a GM HEI module as an experiemnt for about $30. Always good to have a backup anyway.

If it was mine I'd reach up and wiggle that wire around while the engine is running. If something changes you'll know there's a possibility. I might even attach some extraneous metal to the post that the wire encircles. I don't know what exactly happens as current pulses through that small coil of wire but I imagine that it generates a field in that core that passes in to the body of the tach. Then magic happens.

Move the lathe to the car. On-car-rotor turning is a thing. And who checks their new rotors for runout? That's not obvious either! What's going on here!

I can't remember the exact details but I know that people have fiffled with the loop of wire on the back of the tach and had good rresults. I think that they might have removed a loop or made it bigger. It generates an electromagnetic feild and the electronic igntion boxes apparently overload the current sensing system. They pass more amps. As I understood what I had read and barely remember. I think that you can reach it from underneath without removing the tach. https://www.ebay.com/itm/235464345938?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=sQc_o1-rRnS&sssrc=2047675&ssuid=&widget_ver=artemis&media=COPY

Here's what the matchbox expects. Don't know if it will help the tach. From the 1982 FSM.

What is being investigated? It's not obvious.

1972 electronics technology and parts inside these current sensing devices. I found this interesting page on the internet. Might have something for the guys with electronics expertise. Seems like a tachometer rebuild might be in order. The page is a good example of how wrong things can get when a person tries to be clever with page color and font. Easier to read if you highlight the text with your cursor. Not sure of the quality of the information but it's an example. https://www.sw-em.com/Smith's Tachometer.htm

The collector/investor car market is a strange place. https://bringatrailer.com/listing/2010-honda-element-22/

In the States they just stuck on the finned cover and called it good. The 300ZX's got them with the LSD diffs, CLSD for sure and I think the 88 Shiro VLSD. Only 87-89 I believe. The FSM shows maintenance procedures on the CLSD's but no pictures of the cover. It's one of those things to look for for those trying to get limited slip for their early Z's. Like finding gold in the wrecking yard. Here's a typical finned cover. https://bringatrailer.com/listing/1988-nissan-300zx-43/ But this one looks like it might have the plumbing for fluid cooling. Different cover. First time I've seen it. Interesting. https://bringatrailer.com/listing/1989-nissan-fairlady-z-2/

@Mike Edit - but now it has come back. Strange stuff. Probably uncipherable. This thread has disappeared from the Activity page. It should be one of the top ones since I posted three hours ago. But I can get to it through the Notifications links. Weird. Here's the latest on the Activity page. CO's five hour old post is top of the page.