Zed Head

Can you take another picture and pan out to include the timing tab on the left.? Never seen that many points. You need to decide which one you want to use as zero. Grab on to that damper (an engineering/physics word, not dampener) and yank it around and back and forth. See if it's loose. It's been known the that the wrong combination of bolt and washer can leaver the damper loose on the crankshaft. Plus the PO replaced it for a reason, there might be damage under there. That bolt head looks pretty beat up.

In the States the 280ZX changed ratios in 1980. According to the FSM's. 1979 had the older wide ratio 5 speeds, 1980 had the new close ratio. 1980 also had the odd 0.773 overdrive (although I got one from a 1981 car, not sure how it got in there). So a generic "280ZX" remark can be confusing. If you want to see something wild check out all of the differential ratios and vehicle combos for 1979. They kind of went nuts. I've never seen a 3.7 long nose R200 but according to the book they were available. Even the 3.364 R180 is out there, supposedly. And, the 4 speed is still shown.

If the valves are sitting proud of the seats they can warp. AKA burn. It is odd what you're seeing. Might be interesting to take a measurement on 3, put the plug back in, start it and rev it and measure again. If your carbon theory is correct you'd think it would blow off and you'd get a different number.

Maybe you have some sticking valves. Be ready for a rocker arm to pop off.

Sometimes an exhaust leak can sound mechanical. Nissan actually provided a way to monitor chain wear. The notch and groove. Some aftermarket sprockets don't have the notch though.

You are turning the engine the right way but you are pushing on the side that should be pulled by the crankshaft sprocket, when you use the camshaft bolt. Since you're using the camshaft bolt you have to turn the engine backwards. That will keep the tight side tight. But it will also run the chain over the tensioner backwards. If you're worried use the crank bolt and see if the noise is still there. Pull down on the tight side. And if you get your eyeball in just the right spot I think that you can see the tensioner. Or use a mirror.

Is this your 75 with original engine? They have the poor valve seat material. Needs lead.

Wires are affected by current and current results from the draw of the devices at the ends of the wires. The alternator is a pusher. Your battery has all of the energy necessary to smoke all of your wires in to dust, except the giant battery cables, which would probably cause the battery to melt down before they withered away. It would be a contest. Even the cheapest battery has 675 cold cranking amps (CCA) available. They're the same amps that an alternator puts out. Take a small piece of wire and touch the ends to the positive and negative terminals of your battery at the same time for a demonstration. Wear gloves or use pliers. Post a video. Seriously, it will be a neat demo. The battery is just sitting there waiting to destroy your wires. https://www.oreillyauto.com/detail/c/economy/battery---accessories/batteries/31624da3221a/super-start-economy-battery-group-size-26/ssbd/26ecoj/v/a/16439/automotive-car-1971-nissan-240z?pos=9

I came across another variable reluctor system. AMC. Very similar to Nissan's in concept but not so bulky. Also switched to a fancier module as it progressed. https://www.rockauto.com/en/catalog/american+motors,1976,hornet,4.2l+258cid+l6,1004500,ignition,distributor,7108 https://www.rockauto.com/en/catalog/american+motors,1976,hornet,4.2l+258cid+l6,1004500,ignition,ignition+control+module+(icm),7172 https://www.rockauto.com/en/catalog/american+motors,1978,gremlin,4.2l+258cid+l6,1003936,ignition,distributor,7108 https://www.rockauto.com/en/catalog/american+motors,1978,gremlin,4.2l+258cid+l6,1003936,ignition,ignition+control+module+(icm),7172

How do you know it's #6? The brake booster supply hose is back there, and the heater/AC valve vacuum supply. I've noticed that the intake air supply across all six is not even. #1 tends to run lean (whiter plugs, more air), and 5 and 6 tend to run rich (dark plugs, less). Could be too lean from a vacuum leak or too rich because of design.

I wouldn't assume that whatever you might find needs a rebuild. Look around for a complete junked 280ZX or 280Z. Buy the whole car and scrap the rest for $50. As far as the 71A the car will probably be worth more with it installed. Not clear what your long-term plans are. Your problem description makes it not clear what exactly is wrong with it. Might be a simple fix, who knows. Don't overlook just buying a cheap 71B 4 speed while you look for a long term solution. Sometimes people give them away. @Racer X has what you need, probably of all three varieties, but it might take some work to get to. He's right down the road...

Post #33

The external regulator acts as a relay for other relays. When you take it out of the picture and use some of the various wiring diagrams out there for converting you end up closing the circuit to the other relay without realizing it when you jump those wires. The L pin on the externally regulated alternator is a path to ground. So if you see voltage on the wire that connects to the L pin, after you wired the jumpers in, with the key off, then the voltage will have a path to ground with the key off. The S pin sees voltage all of the time, normally. It is not a path to ground. Here's 1982 -

This part does suggest either a bad alternator or a device on the L wire, like a relay, that is powered by the newly jumpered wires. It would be on the L circuit. If you measure voltage on the L wire with the key off then the problem is in your wiring. I had this problem on my 76 with the brake warning lamp check relay but I don't know how the 71's are wired. It should show on a wiring diagram.

You don't have to wait for the new alternator. SteveJ's tests are for the harness. The wire that goes to the L terminal would have to have voltage from the battery in order for the battery to discharge through the Lamp circuit. if the alternator is okay. Put your meter on the L wire in the harness and see if it has voltage with the battery connected and key off. The S wire will always have voltage and could only cause a draw if the alternator had an internal short. Don't overlook that the original wiring might have other devices on the L circuit. S and L are the labels for the internally regulated alternator systems. The top of the T is S, the upright is L.

You can use a meter to see if there's a short through the alternator. You should be using a meter anyway when modifying wiring.

The BAT people take a lot of abuse over that, reporting the correct numbers. Surprising that they did not call it out in their description. As I understand things, BAT writes the description, not the seller. On the other hand though, anyone that follows the 240Z auctions knows to verify that. The bidder, MRM, has bought and bid on several 240Z's. You'd think that they knew what they were bidding on. Who knows. Drama! https://bringatrailer.com/member/mrm/

The market is a combination of enthusiasts (the V8 car went for a good price), collectors (the imperfections detract), and investors (the low VIN number has inherent value that will increase as time goes by). I think that the investor class is growing as the stock market loses value. Hard assets bought by investors who like neat cars. Here's the BAT price plot for 240Z's with a limit of 60K. The trend is still up. Even the low end is up.

The brass nubbin modified switch could be tested with an ohm-meter. If you're waiting to install it to test it with power. Actually, it should be tested with an ohm-meter before applying power. The comment about shorts and erratic device operation are interesting but there are no details. Can't tell what exactly was done.

The Z money is coming back. Three in the 30's, a wide range of styles. https://bringatrailer.com/listing/1977-datsun-280z-84/ https://bringatrailer.com/listing/1972-datsun-240z-255/ https://bringatrailer.com/listing/1972-datsun-240z-201/

LOW VIN NUMBER ALERT! LOW VIN NUMBER ALERT! 🚩 🚩 🚩 https://bringatrailer.com/listing/1970-datsun-240z-96/

My mistake. I was thinking of the front cover. Also remembered some old stuff about the reverse switch. I think you mentioned it in your other thread about doing the rod instead. http://zhome.com/ZCMnL/tech/240SX5spd/Transmission2.htm It's not obvious in the first picture below but he's showing both positions filled with a switch. The original hole and the new hole.

I thought it might be. It's just how he rolls. Hasn't changed. Put a magnet on it to see what it is. Doesn't really matter for your purpose but will confirm zKars's theory. Actually, all he (or the guy that does his work for him) had to do is what zKars's described in his thread, posted above. Weird how that circle got completed...

Big money for a resto'ed 73. It even has the splash pan underneath. Crazy 8's... https://bringatrailer.com/listing/1973-datsun-240z-205/

The videos were telling. Looks like somebody cobbled some parts together and didn't get things completely right. You could make your own switch up on the shift lever. Wouldn't be too hard to do. Where'd you get the transmission? To zKars's point - is the front case with the switch holes iron or aluminum? WRONG!!!>>> I think that the 4 speeds were all iron.