Captain Obvious

I think a direct vacuum line from the engine would work fine. You could install a little check valve in the line so that vacuum applied to that cokk would not be able to bleed off back into the intake manifold. Never a perfect seal, but would probably slow the bleed-off down to the point where that cokk would stay open. Might close down again overnight when the engine isn't running, but as long as the engine is running, that cokk would be forced open. I was only suggesting trying mouth vacuum first (before you invested time running vacuum lines to the engine) because there may be other problems as well. Your heater core might be plugged solid for example. You may have forgotten to connect the heater hoses up in the engine compartment. The mouth vacuum was just a quick way to identify one possible cause for your no heat condition. From where I sit it's the most probable cause, but not the only one.

OK. So no vacuum reservoir, no magnet valves, no nuthin'. You should be able to connect a vacuum line from the intake manifold directly to that vacuum cokk. In theory, any time the engine is running and there's manifold vacuum, that vacuum cokk should be open. If you floor it, you're likely to lose vacuum and the cokk could close, but I suspect that's the least of your worries. So before you go through the effort to run a new piece of tube through the firewall, you could test the theory with just a small piece of tubing and mouth vacuum. I don't know how much vacuum it takes to open that valve (especially one that's been shut for years and may be stuck), but if it's not a lot of vacuum required, you might be able to open it manually.

Yup. Those are the vacuum lines that are supposed to control the system. Although I'm not sure about the use of the word "start". Semantics, but for me, the "start" of the vacuum lines system is up in the engine compartment. My guess is that the ones that are there are dried out, brittle, and have lots of leaks. And what isn't leaking right now, will be as soon as you bump it. That thing in the pic above is a vacuum switch. It's a little valve that directs vacuum line to the appropriate destinations based on the position of the heater control lever. The vacuum line marked "S" is "SOURCE" and it's supposed to be the vacuum source coming from the engine. Up in the engine compartment is supposed to be a vacuum reservoir and a couple little "magnet valves" (solenoid valves) to control the routing of the vacuum. Is any of that stuff present up in the engine bay? The vacuum line marked "D1" is supposed to go to that vacuum cokk on the heater core water line. You really need a copy of the FSM. Download one and read through the A/C section. Out of curiosity, what year is your 260? In the US, the only answer would be "1974", but I think in other parts of the world, the answer could be anything from 74 to 78. I don't know what the UK got. You could probably "bypass" most of the system by running one dedicated vacuum line, but might depend on the year.

Looking at the pics, it appears that your 260 came with A/C. If that is correct, there's vacuum involved. That unconnected device is what Datsun called a "vacuum cokk", and it's purpose was to block all the water flowing through the heater core under some circumstances (like you had the A/C on). It's set-up dead-man switch style and is closed if there is no vacuum present. So yes... That could a reason you aren't getting any heat. There could be lots of other reasons as well, but I'd start with that one. Take a look at the 74 FSM (Factory Service Manual) in the Air-Conditioning section. It explains the function of that vacuum cokk. What is the current state of the system? Vacuum lines present and recently replaced? Vacuum lines present but old and leaky? Vacuum lines non-existent? No idea what I'm talking about at all?

Simple. Because: "All animals are equal, but some animals are more equal than others." - Animal Farm (1945) Not to be confused with "You fukked up. You trusted us." - Animal House (1978)

OK. Then I blame Jon as well. Works for me.

Thanks for the pics. I'm guessing that white thing was originally intended for home downspout connection. To convert from rectangular downspouts to circular drain piping? In any event, it looks like they repurposed that stuff and sealed with polyurethane expanding foam. "Functional is not how I would describe it. " Good luck with the reconstruction project. Looks like most of that is removable. Just a matter of getting your hands on the right parts.

@AK260, So a little bit ago, you suggested that the optimum crank position for peak pressure was 22 degrees ATDC, but the articles we've bantered around suggest that 14 degrees ATDC is optimum. Do you know the origin of your 22 degree suggestion?

Hey Ash, Is that smaller fan housing actually functional? If so, how is the air inlet connected to the firewall hole? Can you take a pic from a little farther back to show how it's situated?

"A bad day in the yard is better than a good day at work. My labor and risking life and limb in snake infested tall grass is free."

So? How about a close-up of one of yours next to a stock one?? And just think... In the beginning, it was a pipe dream and all sounded so difficult!

Counting his, mine, and granny's? About 40.

Awesome. When you said you were going to cut off the excess material on the lathe, I was going to suggest trepanning. I suspected that if you tried a traditional outside edge cut, there was no way you were going to be able to do that mounted on a mandrel like that. The interrupted cut would have made that impossible. Either the part would spin on the mandrel or the corners would have just bent over. Seems you're a step ahead of me! Looks great!

Cool. Just make sure you're careful if there's any fluorocarbon (for example... Viton) in there. Don't get it too hot.

Bummer. I had heard about one of those in my area, but never checked it out. Wonder if they're still in business or if they dried up.

Let me see what I have here first before you send parts. I know I have a complete working unit on my car, so I can take handle measurements off that (assuming they didn't change any over the years). What I'm not sure about is if I have a broken one laying around. I'll take a look when I get a chance. I did have one more thought on a repro technique... Make the whole thing out of metal, but make the handle section narrower than stock (and not tapered). Then glue on a hollow white plastic handle. Or a black one. Or a teak one. Or mother of pearl...

Agreed. I'm assuming weather and heat exposure are the two biggest contributors to the deterioration. Have you got one where it's broken, but you have all the parts still? You could sent it my way and I could poke around with it.

Yeah, I saw that. The quote I'm hearing from a lot of people "Shite just got real!"

Right. Her - "Hey, honey... The zombie apocalypse is coming. What should we do?" Me - "Well I don't know what you're gonna do, but I'm gonna stay home and work on my Z."

Can you post a pic of a working one and also post another pic of what yours does instead?

Absolutely. That would be an easy part for 3D printing. My only concern would be how durable would it be? I'm not sure how brittle that stuff is. My SWAG would be that the original part is glass reinforced nylon. So @jfa.series1, the original parts all snap off where the handle meets the spherical section, right? Another possibility would be to just make a "handle" and drill out a hole in the original sphere and glue a new handle in place? Tricky tooling setup, but might take less time than making a whole new piece from scratch. I still think that painting a metal one flat white would be the best all around solution. I'll just have to carry a magnet with me to shows in the future so I can tell originals from repros and judge the cars appropriately.

Nice. I did the same thing with the Dremel. Cut out the peened section enough that I was able to get the old nuts off without smearing any threads. The post-process lathe work was gilding the lily just to clean everything up and make it look all nice and purty.

I get you bro. !! And I agree with your assessment about the rising VE. And also agree that would be very difficult with springs and weights. Maybe I could whip up some little programmable device to try that. With the state of world events, I guess I have the time to work on projects at home...

Yes we do. That would be quite cool. And thanks for the info links as well. I dug into the one from ls1tech and it led me to another one on that same forum which led me to another good one. Here's what I found: https://ls1tech.com/forums/advanced-engineering-tech/254868-ignition-timing-101-a-4.html and the original article it was based on: http://www.contactmagazine.com/Issue54/EngineBasics.html

Someone with a properly tooled lathe could make this: