Captain Obvious

There is a plastic bushing in the linkage piece mounted to the firewall that started sloppy from the factory and has only gotten worse over the years. It is not replacable as there is a metal joint swaged into place that prevents disassembly. Many moons ago, I rebuilt one, spending a completely unprofitable amount of time milling the swaged metal off so I could take it apart, making a new bushing, and threading the previously swaged joint for reassembly. Turned out great, but I would loathe doing it again. As for the spring and washer joint at the end of the hook... It looks stock to me. Maybe a missing washer between the spring and the linkage? But no... That system was not dreamed up by your PO. Nissan did that.

The linkage piece that mounts in the balance tube is very different between the round tops and the flat tops including the location of the slot where the shepherds hook connects. The round tops require a longer shepherds hook. I'm not an expert at reading the parts fiche, but it seems to me they did use different parts. Goes like this: 12 ASSY-TORSION SHAFT A 18300-E4600 L241 18300-E4601 L24 7206 18300-N3300 L24 7207-7307 18300-N3600 L26 7308-7408 18300-N4310 L26 7409 I'm thinking you're looking for 18300-E4600 or E4601 which were used until 6/72. Your car came with 18300-N3300 which started in 7/72.

My work leads me to believe that they would not absorb fluid. That said, however... If I have a damaged one and a non-damaged one, I'ma gonna use the undamaged one.

I took a quick look into this and I think the female contacts are Junior Timer (not JPT, just JT). Here's some pics and part numbers for you to dig around with. 825213-1 - This should be something close to the ECU mounted male tab connector: 827663-5 - This should be something close to the harness mounted female contact connector: And here's an example of the female junior timer contacts: I took a look at the harness I have here and it appears the contacts have a gap between the fingers, and this modification shows up in one of the catalogs as a "special version". Looks like this: If you need part numbers for junior timer contacts, let me know, but I suspect armed with the above, you should be able to easily turn up something that will work.

I could easily attribute a 0.2mm difference to manufacturing tolerances or measurement variability. Maybe there's a burr kicked up on the piece you measured as a result of the shearing or forming operation?

Hmmm... I thought they were junior power timer as well. I've got some connectors here. I'll take a closer look when I get the chance. I'm headed out of town today, so it won't be for a couple days, but when I get back, I'll look into it.

Another fail: "Using a feeler gauge, measure the gap between the rocker arm and the valve stem." Not happening...

He hates these cans!!!

I started putting some of it here: https://www.classiczcars.com/forums/topic/67864-ignition-systems-analysls/ But it kinda fell by the wayside?

Absolutely. Don't misinterpret my skepticism about location of the resistance (AKA "ballast"). The points you're bringing up are good stuff and completely valid: Yes, having the ballast resistance outside the coil will also keep the heat generated in that resistance outside the coil. And yes having an external ballast resistor allows for the ability to short across that resistance during engine cranking which could help providing a healthy spark even when the starter current is dragging the system voltage down due to it's large load. If the current limiting resistor is inside the coil, you lose that feature. I'm just thinking that if you've got a good enough ignition system such that you can still easily start the car even while the starter load is pulling the battery voltage down .and. you have dwell length in control in such a manner that you are dissipating a small amount of power in the coil, then it should not really matter where the resistance is. Either inside or outside the coil would be fine. But getting back to the OP's application, I guess the question is "Does the 75 ignition module meet those two above criteria?" I've never opened up a 75 ignition module. I've reverse engineered the 77 and 78 and done a bunch of poking around with the matchbox modules, but I've never opened up a 75. I would expect it to be similar to the 77, but I really don't know for sure. Maybe the 75 module design is weak enough that you DO need to defeat the ballast during starting, and maybe the dwell control is looser than the later versions of the module? Clearly by 78 they thought the module was good enough that they could use an internal resistance and eliminate the external ballast.

I'm unconvinced. That article (which I must say was very poorly written*) talks about the concept of a "fixed ballast resistor" which is what the ignition system uses. They also referenced a simple LED circuit with a fixed resistor being used as a "ballast resistor" in the circuit. So it seems that a normal fixed resistor can be a "ballast". Same with the fan example. Granted, ballasts that are designed to purposefully change their resistance as the temperature goes up is a thing. And active ballasts like they use in fluorescent lights are clearly a thing too. But those are specifically designed to change their resistance as the current through them changes. I will dig around a little and see if I have a Z ballast laying loose around here. If I do, I will try to see if I can measure resistance changes with respect to temperature. I mean... Pretty much all things change resistance as their temperature changes, but I ought to be able to tell if the ignition ballast changes are "on purpose" or not. * that article seems to be a modified version of this page. Not sure which came first, but this one is (slightly) better written? https://www.electrical4u.com/ballast-resistor/

I'm not sure which "he" you're talking about at this point... If you talking about your buddy with the 75 using a 1.6 Ohm coil with the stock 75 ignition module, then I think he is only 0.3 Ohms off from stock, not 0.8. The stock 75 coil was 0.5 Ohms paired with a 1.3 Ohm ballast. The result is 1.8 Ohms total. Is your buddy using a non-stock 1.5 Ohm coil instead of the stock 0.5 Ohm coil?

So now that we've got all this distraction in this thread... I hope the OP has solved his issues!

Didn't do what from the start? The current limiting? I'm thinking that as technology progressed and emissions and performance requirements got harder to achieve, they made the modules better. It takes a couple more components to do the current limit and those components cost a couple pennies. Looking at the insides of the modules, you can see the transition of the development technology from early seventies to late seventies. The early ones are metal can transistors on a PCB that was clearly laid out and taped by hand. And then by 77 they were using plastic case transistors on a CAD digitized board. The technology of both the parts used and the tools used to design that kind of stuff was moving VERY fast. Kind of a transition period in time.

From 74 through 77 they used a 0.5 Ohm coil and a 1.3 Ohm ballast resistor. Then from 78 through 83 they used as 1.0 Ohm coil and no ballast resistor, but they also put an "on-purpose" coil current limit built into the ignition modules. Pre-78 modules had no such feature. So Datsun wanted the 74-77 modules to be paired with a 1.8 Ohm resistor (except when cranking in START), and they wanted the 78-83 modules to be paired with a 1.0 Ohm resistor. I assume those pairings were somewhat derived through experimentation and analysis at their end. So I'm no ignition expert, but here's my read getting to the meat of your question.... "Is it OK to run the ZX matchbox module (which was intended to be paired with a 1.0 Ohm coil) with a 71 coil instead?" I just took a look at the 72 FSM and it says the coil resistance is 1.6 Ohms. Using a 1.6 Ohm coil with the ZX module would result in the coil current being lower than as-designed, but if it runs OK and doesn't break up at higher RPM, then I'd let it be.

That's ridiculous. Nobody in their right mind does that.

The original ballast resistor nominal is 1.3 Ohms . And the original coil spec is 0.5 Ohms. The total nominal resistance of the two in series is 1.8 Ohms. (Page EE-45 of the 75 FSM) I'm thinking that with a 1.5 Ohm coil and no ballast resistor, you're very close to stock. You've just moved the resistances around. And since everyone likes pics:

Haha!! Yeah, I got all excited when I saw someone working on a 260. Then I saw the note about the round tops.

Round tops. Or I would have been involved at the start.

What he said. And it doesn't matter whether you are tightening or loosening. The mechanics of the static friction are the same. I'm not trying to cast dispersions on your work, but what I'm saying is don't get all caught up in the absolute numbers you think you are seeing. I'm saying that just because YOUR wrench doesn't click until 50 ftlb on a fastener that was supposed to be torqued to an upper limit of 40 does not convince me that bolt was originally torqued higher than the spec. So you've got an engine with a bunch of time and heat cycles on it. And when you used your torque wrench (with some unknown accuracy), it took more torque than spec to move the bolts that have been in there for some time. No surprise there.

I'm not a mechanical engineer, but I have serious reservations about using the torque required to crack a bolt loose to determine what said bolt was originally torqued to. I mean... I bet it's proportional (like the more it was torqued to, the more it would take to break it free), but as far as determining absolute value... I'm very skeptical. @Wally, You just torqued your main bolts to 38 ft-lb, right? Put your wrench back onto a couple of them and see what torque it takes to remove them. See if it takes 38, or if it takes more than that. I bet it takes more. Static friction is higher than sliding friction and all that?

Well I have my doubts about the theory that those marks were from an attempt to expand the end of the shaft, but who knows. I wasn't there when they did that, but I would have expected that someone who thought they knew enough about such maneuvers would have done a better job. Forensic analysis from my comfy chair shows file marks on the end of the shaft. Further, the fact that the upset areas around the screwdriver divots do not exist, it would be my suggestion that the upset "burrs" around the craters were filed off. And since the shaft does not sit proud of the hole it is recessed in, that filing operation must have occurred after the impact operation. Presumably in an attempt to make it look better? LOL! Whatever happened, it's gruesome.

So out of curiosity, how did the leather dash people make the contours fit? Did they do it with sewn seams? Got any pics of one of them installed?

Probably just me, but when I see the 240 dash, I see this: