Mixelplix

Simplegreen at first, claybar second, buff third

I personally would strip it just for peace of mind.

As a follow up to this conversation (and hopefully help to anyone with a similar problem). I ordered and replaced the exhaust manifold, and it did not correct the problem. Grasping at straws, I decided to order two rocker arms, and lash pads. I removed and inspected the rockers and lash pads on cylinders 4, 5, and 6 and discovered that the lash pads on cylinder 6 were worn more than the others. I replaced the rockers and lash pads on cyl 6, and it's quiet as a mouse now. I suspect my oiling bar was not properly lubricating cyl 6. I also suspect my cam has wear on cyl 6, but I'm going to leave it for the time being.

I'll do that tomorrow.

I assume I'd be able to feel a dead valve spring by applying pressure to them? Should it be obvious? In my years if screwing with cars I've only ever seen broken valve springs... Do they have the ability yo just loose their tension?

Attached is the YouTube video. 260z valve rap: 260z valve rap - YouTube

Thanks for the heads up Sean! While I'm running the OEM cast manifold, I'll definitely take more time to inspect the head to manifold bolts for tightness. I couldn't see any logical reason why my cast manifold would warp overnight, so I think that's ruled out. From the manifold down is headder wrapped however, so I'll take a close look at that too.

As an update, I got a chance to jump on this a little last night. I adjusted the valves in question both much tighter, and way more loose and the noise still persists. I'm convinced it's valvetrain noise - but I'm at a loss as to why it's so much noisier all of a sudden. I'm going to try to take a video and post it tonight.

When you say rock the rocker, do you mean front to rear, or drivers side to passenger side? Both my 5 & 6 exhaust rockers seem to move a tiny bit more in the front to rear direction than the other ten. And I mean such a tiny amount that it might be placebo effect. And do you mean loosen the lash when you say 'take some out'? My mouse trap springs are ok. It did make the noise before... but it's more pronounced now (both because the valvetrain is overall less noisy, and the rapping noise became louder.

On your suggestion I retightened the exhaust studs. Number 6 was loose, but it didn't effect the noise. Zed Head, I know how you feel. My Land Cruiser is the same way. However, this noise is so loud that it's literally a spectacle. I had one of my non mechanic friends say 'There's something broken in your motor'.

gear backlash can only be checked with the diff opened up.

I agree with improper lash on the ring and pinion. I've had to redo my land cruiser for the exact same reason. To describe it as best I can: It's a powerful reverberation bass noise that comes on suddenly and doesn't go away.

Just a little more info: It runs and idles excellent. The compression is terrific and equal across all six cylinders. I do lose a little oil from valve stem seals (slightly at first start up, and under heavy throttle).

While slowly reconditioning my early 74 260z, I decided to do a valve lash adjustment. After I was done I was able to notice a significant valve train noise somewhere around cylinder 5 or 6. The noise is sharp and follows the RPM. It's the same hot or cold. With a stethoscope it appears to be more loud on the passenger side. It makes the noise regardless if the spark plug wire is plugged in or not. I've triple checked the lash both hot and cold. And they're extremely close to perfect at .008 intake / .010 (cold) and .10 intake / .012 (hot). My oiling bar is recently cleaned and silver soldered by me, and I visually verified that it is working (what a mess). I believe it did make the noise prior to the lash adjustment, but it's definitely louder now. The cam looks fine, the wipe pattern between the cam and rocker seems fine, the springs and retainers are all there and not obviously broken. I'm not a novice mechanic, but nearly all of my experience is from much newer cars. What procedure should I follow to figure out what the problem is exactly? Desmond