Zed Head

What procedure are you using to adjust rocker arm clearance (lash)? If it ran fine before then your work must have done something to change something. Are you rotating the engine and camshaft as you measure and set lash to be sure that each lobe is on the base circle? Seems like a very loose rocker arm is the most likely possibility for that kind of noise and the work you did, considering that it "ran fine" before. Don't really see any other moving parts in the engine that you touched that could cause it.

That noise still sounds pretty solid. Like objects with large mass. I'm changing my guess to rod bearing. Or not. Can't really tell. Your videos are at idle. What happens if you rev the engine?

Search "280Z tachometer" and you'll find pictures of the plug out of its socket. Might give you the confidence to pull harder. My tachometer used to stick when the weather got warm. The capacitive discharge ignition systems are well-known for causing tachometer problems. MSD, Crane, etc. Might be worth your while to reconnect the old ignition module and see if the problem goes away.

Here's your historian. @Carl Beck

Somebody stuck a fill plug in the drain hole, probably because the socket type drain plug is a pain to remove. Browse through these listings, below, and you'll find a few pictures of the original setup. I don't think that Nissan did any "one-off" plug arrangements. You should post the replacements that are not of this type just so that people can see them. Might be an aftermarket guy offering an improvement. https://bringatrailer.com/datsun/240z/?q=240z

One of the great ironies of the situation, and one of the reasons that I believe in the vaccines, is that any pharma company that released a vaccine that damaged people would get destroyed in the stock market. The spotlight is so bright that they would not be able to BS their way out of it.

The point was that FDA approval is not worth much. I think that overall we got got lucky that there are good individuals in these various bureaucracies that know how to work within them to get good things done. But eventually the bureaucracies will get so corrupted that nobody can get anything done. It's already happening in branches of government. Let's hope that some rebuilding happens after this close call. And be thankful for the people that pushed the working vaccines through. If you believe the reporting, they actually work, with no side effects. I feel fine.

The Black Box. Probably would have had to get a "Q" clearance. Q used to mean just a certain level of security clearance. I assume that "Q", whoever Q is/are, has/had a Q clearance, hence the moniker "Q". Anyway, you missed out on the whole Boeing culture in the PNW. Work hard, get laid off, collect unemployment knowing that the cycle will repeat. I had some friends in the Boeing world. No offense Racer I don't know if you're an engineer or not. But there really is a "Boeing way of life" out here.

The FDA is not really what people think it is. It suffers from serious "mission drift". It needs a major overhaul. https://www.reuters.com/article/us-health-coronavirus-vaccines-fda-exclu/exclusive-top-adviser-steps-aside-from-fda-covid-19-vaccine-reviews-over-potential-conflict-idUSKCN26E3IW https://ethics.harvard.edu/blog/risky-drugs-why-fda-cannot-be-trusted

Some work with a meter and a battery, should do the job. Measure resistance and direction. A fun project.

Different cars, for sure. The 120 is the one you want, apparently. I wonder which Ford used it.

There's a 120 and and a 121. The 121 says "Jetronic", the 120 doesn't. Wonder if diodes/resistors is the difference. I know that their typical 5 pin relays come in different flavors. Same basic functions, just some have a few extra parts inside. Usually they show it on the cover, but these don't. Edit - the 121 has 13 pins vs 11 for 120. Not sure how that affects things. Haven't studied the pin diagram. https://www.amazon.com/Bosch-0332514121-BOS0332514121/dp/B006NYJ328 https://www.amazon.com/Bosch-Automotive-0332514120-Relay/dp/B004Z0W1C6

Fundamental red 71. https://bringatrailer.com/listing/1971-datsun-240z-60-2/

There's actually three of them. Family operation. https://www.motormanfuelinjection.com/contact.html They might have a new version also. Never know. https://www.motormanfuelinjection.com/location.html

I think it's the same guy. The site shows that his focus is on the parts not the hype. When he put that web site together I think it was state of the art. Look at all of the information on it. Use the contact page. Call him up. It's probably a land line to a rotary phone. https://www.motormanfuelinjection.com/request-form.html

Just came across this one. Who knows what the innards look like. The problems don't show on the outside. https://www.ebay.com/itm/174753879999?hash=item28b02497bf:g:JK8AAOSwzOhgjcRl

I posted the wrong Motorman link. Need to fix it. I'd just go directly to his web site. Says $29.99 for the Bosch injectors. Bosch is good quality. His web site is prehistoric. But he has survived. https://www.motormanfuelinjection.com/NISSAN_FUEL_INJECTORS.html

When parts get scarce the stores mark things up higher. I'm pretty sure that many of them just buy from Rockauto and resell. The Datsun Garage part listing doesn't say "new". They look like these remans. Edit - I copied the wrong link here too. This is the right one. Very similar to Datsun Garage. https://www.ebay.com/itm/201509531117?_trkparms=aid%3D1110006%26algo%3DHOMESPLICE.SIM%26ao%3D1%26asc%3D20200818143230%26meid%3D621deb4a130e45adb2d2f8e5e1c2cc31%26pid%3D101224%26rk%3D1%26rkt%3D5%26sd%3D201317301856%26itm%3D201509531117%26pmt%3D0%26noa%3D1%26pg%3D2047675%26algv%3DDefaultOrganic%26brand%3DNissan&_trksid=p2047675.c101224.m-1

I think the reality of aftermarket parts is that a cleaned, refurbished and tested OEM part is often better than a brand new aftermarket part. OEM parts are designed to last tens of thousands of miles. Aftermarket parts are as sketchy as reman OEM, I think. Worst is probably a reman aftermarket part. I think that all of the aftermarket parts come from the same few places. Standard is a big one. Don't spend big money from a big name shop just to find out it's a $45 Standard product that you could get from Rockauto. People like these Standard injectors. https://www.rockauto.com/en/catalog/nissan,1976,280z,2.8l+l6,1209226,fuel+&+air,fuel+injector,6224

I'd check eBay. Motorman is a reputable refurbisher. Been around a long time. https://www.motormanfuelinjection.com/NISSAN_FUEL_INJECTORS.html https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2499334.m570.l1313&_nkw=280z+fuel+injectors&_sacat=33554

Where do you see $450? The auto store injectors are pretty good. Looks like you can get them for under $60. $360 total. Still spendy. https://www.oreillyauto.com/search/v/a/6637/automotive-car-1978-nissan-280z?q=injectors

Here you go, with one old post. It was SteveJ, and maybe Captain Obvious before him. Not sure if EuroDat is in there or not. (The Share thing is not working right, try this one.) Just go to post #42, Share is messed up.

I have a vague memory of @EuroDat posting about this. You should put "Bosch relay" in your title. That will catch the eye of the people who know.

@Terrapin Z might have a used set. Or @zKars Anybody who's had a few Z's starts collecting. Stuff that they'll never use.

Any Z or ZX from 75 - 83 would work. Also the early Maximas with the L24E. And various Volkswagen Super Beetles. There's actually not a lot in the wrecking years anymore though. I think that I got lucky because the government was doing their cash for junkers program so a lot of Z's, ZX's, etc. ended up in the wrecking yards in my area.