Captain Obvious

What Mark said... What kind of oil did you use to fill the damper tubes on the SU's when you put them on? It sounds like a classic case of too thin of an oil or a damper dashpot not working properly. Can you elaborate a little on the "chatter" you mentioned with the pistons? Any chance you can take a video of that?

To answer some of your questions directly... The initial mechanical setting of the float level is just to get into the ballpark. The sight glass is the real test. The desired level does depend on the carb design though. What year are you working on? 73 or 74? Can you post a pic or two of the power valves? That's another easy way to know for sure. However, without even seeing the carbs, I suspect the fuel level should be right at the dot in the middle of the window and your level is way too high. Tips for cracking the power valve open? Not really. The gaskets hold tight and can make it difficult to separate the wafer stack. Other than brute force, I don't have any suggestions. And testing the carb off the car? I don't have any way to do that. If it was running great one day, and then the next day it wouldn't start at all, I'm not convinced that it was a carb problem in the beginning. But now that you've opened them up and let the magic out, there might be one now. Did you try starting it by holding your foot down a little on the pedal while you cranked it?

Wow Geoff, So sorry that happened. Glad everyone is OK. I'm gonna stop complaining about my car problems now...

Shhhhhhh..... Zed Head, I could take the back half of the cam out easy. Maybe I'll do that (if I can sneak some time in the garage when I "should be working on other things")

Excellent. That all makes perfect sense. A cold lean idle is an unhappy idle. You want every molecule of air going through the venturi, not around it! Glad you found it!!

I haven't decided what path forward I'm going to take, but whatever that path, I will be sure to take pics. I did not look for stuck valves. I haven't done anything else beyond that short video clip other than go out to the driveway and open the hood on the 83 and look inside. I was NOT getting bored. I'm so backed up with car work at this point that one more thing is absolutely not desired at this point. In fact... I'm cleaning up after dinner last night and the hot water coming out of the tap is way hotter than usual. Dangerously scalding hot. Take a look a the water heater and it's got water dripping from somewhere out the top. Not good... I killed the breaker. SWMBO isn't going to appreciate cold showers. Especially if I'm out in the driveway working on my car. Anyone want to help me wrestle a water heater down into the basement? I'm getting too old for this crap.

First time I hit the key, I just wanted to see everything rock around like it's supposed to. It was so striking that I had to do it again. I was like "Wait.... What???" I was stunned. Took a couple seconds to sink in, and then I was really bummed. So what are the prospects for bent valves? Is the L28 an interference engine?

Haha!!!

No, I do not. The one in there is an "A" grind from 1977. I've got an F54/P79 combo here from an 83. That might be the same cam, but if I'm going into that motor, it's for the intention of dropping it in where my existing motor is. LOL. Maybe I will! Bug spray and sunscreen!

Haha!!!

I bought this car used a couple years ago, and I don't know the history of the engine. I did get some pics from the PO including some shots with the head off the engine, so I know it's been apart at least that far. I don't know if he ever pulled the cam off the head or took the towers off the head. It's stock parts (cam is Nissan "A" grind stock), but I don't know if it's original to this car. I suspect that it is, however. I've been driving this car on that engine since I bought it, and have never had a hint that I had trouble like that brewing. No idea what happened. I was not at high RPM's when it let go, and I don't think I've ever hit redline with that engine. I take it to maybe 5K often, but that's about it. Anyway, no idea why it finally let go, but it's gone now! So I haven't dug into it at all and don't know if that rear cam section is seized in the journals. I kinda doubt it. I suspect it spins just fine. I'll find out when I start taking stuff apart. And about a path forward... I could either put a new cam in that engine, or... Exactly what I was thinking as well. I kept telling you I was going to do it this summer, right? The only problem is that it's Z driving season right now and it would be faster to toss another cam into my existing engine. Yeah, me either. That's the "whatever remains, however improbable, must be the truth." part!

Sorry guys. I was trying to be cute and I guess the issue doesn't come across so obviously in the video. That's what I get for holding my antique crappy camera in one hand and reaching in with my other hand to crank the engine. If you look at the camshaft while I'm cranking the engine, you'll notice that only the front half turns. The back half doesn't move at all. My crankshaft completely cracked into two pieces. This is just behind the center support bearing:

Uhhhhh.... Did you watch the video?

So I'm out driving around today, just minding my own business... All of a sudden, out of the blue, it starts running exceptionally poorly. Somehow (still not sure how), I managed to limp it about five miles home. Get home and start the troubleshooting. It's completely missing on the rear three cylinders and front firing out the intake like the timing is way off. So, what can cause a complete miss on the rear three cylinders and run like turds on the others? ECU? Nope. That's not it. Dropping resistor? Nope, not it either. Bunch of lash pads fly out? Nope. "When you have eliminated the impossible, whatever remains, however improbable, must be the truth." https://youtu.be/4nE4QhK4LMY Woof.

Everything on the engine works better when warm. They really don't like running when cold, especially at cold idle. In fact, that's why there is usually some sort of idle speed boost method employed that can be engaged at cold idle. For the 240 and 260 Z's, that idle boost is built into the choke mechanism. And for the 280's that function is performed by the AAR. The point is... If you are not employing the use of some sort of cold idle boosting method, or if your boosting method is not artificially raising the idle enough, then it would be perfectly normal for the idle to go up as the engine warms up. Other thoughts? If you are having some issues when you first hit the throttle you may be running a little lean. A lean cold idle is an unhappy idle. If you're running a little lean, the idle would get better when the engine warms up. That all seems to dovetail together. Sounds like you feel reluctant to come to the forum for help? Don't worry about that. Bring it.

Yup. That one with the bruised nose is my local buddy's. He was going to fix it, but he got lucky and turned up a replacement instead that was in really great shape. The luxury he had was that he was not in a hurry at the time and wasn't under the pressure from a painter to get parts yesterday. No prob. Glad to (try to) help.

For the collective, here's a pic of the dent on the nose of the hood I mentioned above. For those of you with body experience... How hard of a repair is this? I know everything is repairable with enough time and effort, but where on the scale does this fall?

Sending you PM...

I believe my buddy @GGRIII (you met him at my place at the wheel bearing party) has the original hood from his 260. It has the traditional parking lot dent on the front point, but other than that, I believe it's straight. He was going to fix it but found a near perfect replacement instead that saved him some time when he did his car. Would you like me to find out if it's for sale or if he had plans for it?

I sure do and I bet I'm not the only one!

LOL! Whew!! Close call!

I've got a tiny (tiny) bit of molding experience, and in my miniscule experience, it can be really really hard to fill a cavity and have all the air be properly displaced by the filling liquid. Since the block and head (not to mention the heater system) are rough and complex internal shapes, I would be very very surprised if you can just pour water into the radiator cap hole and have 100% of the air in the system be exchanged with water on the first try. I bet there would be significant pockets of air remaining after the fill. And that's where the overflow system comes into play. Putting some rough numbers on it... The volume of air in the system will expand closely related to the ideal gas law, while the volume of water in the system will expand at a much smaller rate. Quick search on the web says the volumetric coefficient of expansion for water is .00021 while air is .0036 . In other words, for the same temperature change, air expands about seventeen times more in volume than water does. That can certainly cause a vurp. It is my belief that the air will eventually be trapped in the filler neck as bubbles circulate in the system. The filler neck acting as a vertical trap as the bubbles flow by and getting pushed out the overflow when the system pressure increases. Then (assuming an overflow bottle is connected and has liquid in it) when the system cools down and contracts, it will pull liquid back in where the air used to be. I also do not believe this happens all at once, but can happen over a number of warm-up / cool-down cycles after filling. So... The bottom line? I think you should connect up the overflow tank, put some coolant in it, top off the radiator, and then heat cycle the system a couple times. If you are watching the tank, you might even see some bubbles burp out. If that's the case, the level in the overflow tank will end up a little lower than when you started because some of that liquid will be pulled into the system. And after a couple cycles, hopefully you would have all the air worked out.

My point about the gas being compressible means that it might not be fine. Just because it doesn't overpower the spring in the cap and push anything out, doesn't mean it's OK. In fact... When the system is working properly, there is SUPPOSED to be some liquid pushed out of the cap and into the tank. Then when it cools, that liquid is supposed to be pulled back in. With the cap on, if you aren't getting anything at all pushed out, that is another indication that you might have air in the system.

About the burping... I suspect it could just be an air pocket somewhere that hadn't worked it's way out. If you've got a gas bubble anywhere in the system, it will expand a huge amount compared to an equal volume of liquid and can push vurps of liquid out like that. The recovery tank and two way valve built into the radiator cap is intended to eventually work that gas out of the system and replace it with liquid. The gas is also compressible though, and it will compress first, before the system reaches the cracking pressure of the cap. If you have too much gas in the system, you may never even reach that cracking pressure because the gas will just compress. So with that in mind... Do you have a recovery tank installed or are have you been running open system?

Why yes... Yes, it does. Enjoy.