Captain Obvious

The flat top pistons for the F54/P79 system stick up a half millimeter (,020 in) out of the block above the deck. I measured the thickness of a used factory gasket for that combo to be about 1.2 mm (.047 in), I don't know if the earlier years head gaskets are thicker, but for the later years, it seemed to work fine.

For failures like that, typical SOP where I come from is to solder jumper wires over the damaged section (like the PO did), but do it with a little higher quality workmanship. That board looks simple enough that you could probably daisy-chain point-to-point wire the whole thing. Do you have a need to lay down new copper where the damaged trace is, or you just want something that works?

As I mentioned before, based on how clean everything is on the valve train, someone has been in there, and very recently. Way more recently than even 30K miles ago. Today's oils aren't going to keep things that clean, and certainly not 1978's oils. I'm thinking someone had the head off right before your bought the car? That thing is cleaner on the inside than it is on the outside! So what are the paint marks on the cam? Is that a "7" I can see in the one pic? And paint stripes on the tops of all the followers?

I know, and I agree completely. I was just making a joke about the nickname your mechanic coined said some time ago.

And the guy who made preparations A through G. They were complete failures.

Woof. Still considering yourself "lucky"? So you're thinking oil getting pulled up past the rings and then getting sucked out the intake valves into the plenum?

Looking at the cleanliness of that valve train, it's clear someone has been in there not many miles ago. How far are you from Flemington?

So this welded cutter you talked about... You're not using a boring bar in a boring head? In your close-up pic, that's what it looks like. But surely you're not thinking of welding the bar INTO the boring head, are you? I was being sarcastic above, but now that you brought it up again, I'm wondering if you're serious, or I'm simply confused as to what your cutter consists of. So you got a mill-drill. We're not judging. I was going to ask before, but thought you had set-up worked out... Can you mount the bell housing trans side up so the hole you want to bore is closer to the head? Or is the bell then too large to get enough clamps on it to lock it to the table? If you can mount it that way, you'd have no problems with Z travel length. They call that "piloted" as in you're using a "piloted cutter". Not uncommon, and a good way to achieve higher accuracy, especially in flexible set-ups.

Yup. That's what I meant with a standard indicator. Doesn't have to be the fancy co-ax. The co-ax just keeps the reading dial facing forward and makes it easier. Not required, but easier. I use my very old Starrett "Last Word" most of the time. Chuck the tail up in the spindle and take her for a spin:

Pretty sure you know this already, but it'll be more accurate if you don't try to do it all in one pass. Flex and all. I would consider a hundred thousandths cut relatively aggressive. And if you're looking for a great cutting oil for aluminum... WD-40. And your spot weld idea is fantastic. I've got a cabinet of boring heads with the bars welded in for specific diameters. Said no machinist ever.

LOL. It's a calling. And for the record... I've never done anything like that. Ever. For sure. Never. Especially when threading. Where's the growing nose emoticon?

Nice! The tooling store works fast for you! I'm guessing you already had the boring head, but just kinda forgot about it? MT3 spindle on the mill? Make sure you have the cutter in the right way... The way you have it now your gonna have to run in reverse. You have a back-gear on the mill? And the co-ax indicator isn't a top priority piece of tooling, but it sure is nice when you get to use it. You could just mount a traditional indicator in a collet in the spindle and spin that. The co-ax indicators are nice because you can keep the dial facing forward and don't need to peek around back to get the reading when the spindle is halfway around or at 270 degrees.

I know you know this already, but you always need more tooling. Always.

Simple... I wouldn't have to create anything. I'd use a boring head who's purpose in life is to do exactly what you described. And if your mill is R8 native spindle, you can skip the collet as well. Use a small one (like 2 inch) and dial it in. Easy-peasy. And as for the centering, I wouldn't mess around with that either. I'd whip out the Blake co-ax and indicate it in-situ. Blake is expensive, but there are far-east options that won't blake the bank. If you don't have a boring head, or a co-ax, you could resort to a fly-cutter and an edge finder.

I got this available:

I took a look at the FSM to refresh my memory, and the ring gap should be measured at the bottom of the bore where the wear is the least (77 manual EM-15 bottom left). Makes sense since what you really don't want to have happen is for that gap to close up to zero when things heat up. You're a couple thousandths smaller gap at the bottom of the bores, right? I'm no engine rebuild expert, but I think you're fine.

Wait... The earth is a toroid?

I just looked up the SDS for Purple Power, and the main cleaning agent is sodium hydroxide (lye) which can be an issue for damaging aluminum. Looks like a quick ten minute spray and rinse is OK, but I wouldn't dunk the pistons in it and leave them overnight. 1. Sodium Hydroxide 25% Concentration 3 - 4 % (weight) CAS no. 1310-73-2 2. Chelating Agent Concentration 1 - 2 % (weight) CAS no. 67401-50-7 3. Diethylene Glycol Monobutyl ether Concentration 1 - 2 % (weight) CAS no. 112-34-5 Notes - I looked up the chelating agent and it's Ethylenediaminetetraacetic acid (EDTA) and the last item is an organic solvent (2-(2-Butoxyethoxy)ethanol. Reference - https://f405ae25-bd48-4e9f-92a9-0f03256f19bb.filesusr.com/ugd/14ad0e_342940d078d94505b11d1358c997718c.pdf

Clean enough to eat off of!!

I pulled my ultrasonic off the shelf a couple days ago to see if it was large enough to fit the piston top inside to clean the ring grooves, and it's not only large enough for that, but it's actually large enough to accept an entire piston AND rod. Sounds like I should get myself a bottle of Purple Power as my cleaner liquid for the US!

Question for the collective... So what was the deal with this car? He bought it at Mecum for 12.5K (plus buyers premium) in April and everyone went nuts for the car saying "He stole it at that price" and he could instantly flip it and make $$thousands$$: https://www.classiczcars.com/forums/topic/62036-my-mecum-purchase-1972-240z/ He put about $4K into it: https://www.classiczcars.com/forums/topic/62036-my-mecum-purchase-1972-240z/?do=findComment&comment=577203 And then started trying to sell it in July. Didn't sell for 25.5K: https://www.classiczcars.com/forums/topic/62553-saturday-houston-auction-of-my-1972-240z/ Didn't sell for 23.9K and didn't sell for 19.9K: https://www.classiczcars.com/forums/topic/62704-for-sale-1972-datsun-240z-23900-or-best-offer/ And then in the end, it finally sold for 15K plus commission: https://www.classiczcars.com/forums/topic/63201-auction-for-my-72-240z/?do=findComment&comment=588925 So I've passed on a couple 240's because I wasn't sure I could get my money back and ended up kicking myself a little later because they sold later for a good profit. But then this example comes along and that does not happen. Anyone have any insights as to why? Is it just a fickle market?

I think that comment is simply a reflection of the available ranges for current measurement. Those reviews look to me like they were written by "electricians" who spend their days working on 120-240 AC circuits. House wiring and appliances. They are making a distinction between that type of work, and the "electronics tech" sitting at his workbench troubleshooting a radio. They're implying that the guy working on radios might need something better for measuring low currents in the milliamp or microamp range. My thought is that even though there are some "really small current" devices on the Z cars, I don't think most people would need a meter to mess with them. Things like fixing a radio, or the clock. And that other stuff about spurious "ghost" voltages and stuff? Scares me more than it seems like a feature. Best I can tell is they're saying that "ghost voltages" are sources of voltages that have a high source impedance. Goes like this... Your normal voltmeter draws very little current in order to make it's measurement. In fact, the lower the better. You want to draw very little current, because any current you draw with meter will affect the reading. But they're saying that in "electrician" work, you can run into the situation where you might read a voltage on something (their video measured 4V between H and G on a power strip), but they're saying that if you switch over to their "LoZ" range, it will show you zero volts. The implication is that when you apply a load to that voltage, it drags it down to zero because the source impedance is so high. Frankly, I'd want to know where the high impedance bleed over is in my circuit that is allowing me to read 4V where I should be reading 0. What's the threshold for ground fault interrupters anyway? The 117 also has a non-contact voltage alert range, but I'm sure you've already got a pocket sized non-contact indicator you've been using for years and already trust. I'd just stick with that. Personally, I'd always measure it before I go sticking my hand in there, regardless of what a non-contact indicator says. My bottom line? I don't think there's anything on the 117 that you would need over the 115 unless you want to toss out your old non-contact indicator and want to start taking the 117 to the job site.

I'm thinking our introduction to tranny wrestling occurred at about the same time and on the same vein of cars. Ahhhhhh... the smell of gear oil in your hair. Good times... Good times!

I'm not sure what they mean by "consistent spurious currents". Have you got a link to the discussion?

You've got a lathe, right? That bushing should be easy-peasy!