Am I positive? No. As I said I couldn't really pinpoint the sound as it started raining. It was loudest at the rear of the motor on the flat part of the transmission. Now is this where it's coming from I can't tell you. I will be doing more tests tomorrow or later this week so I'll know more as the weeks progress.

Jan

Ding-ding-ding.You win a Kewpie doll.

As quoted above it is in fact the timing chain rubbing. Thanks guys for all the help

Jan

That was mentioned many times on the first page. (Just sayin') Anyway, glad you found it.

Well sadly replacing the timing chain did not fix said sound. I'm not saying it wasn't needed as the old chain was about an inch longer than the new one and the tensioner spring was roughly a third of the size of the new one, so it wasn't all a waste. Atop that the cam was off time and there was about an inch of sludge in the oil pan, so it was most definitely needed.

Anyhow the sound has now become more localized from when it first appeared. For what I can determine (and my mechanic I go to) the sound appears to be coming from the mid to rear section of the valve cover.

Before I go further this is what occurs. The sound only appears between 1 and 2K on the tachometer. Only does it on deceleration (not on acceleration) it doesn't really vary with pitch or frequency even if I go up to 5k and release the throttle, it seems to be rather constant and only occurs at said specified ranges.

My mechanic suggested that maybe one of the rocker arms in the motor is wobbling or moving when decelerating (that is load being taken off). Any ideas guys? This is rather annoying.

Jan

Well I guess you just have to pop that valve cover off and set it straight. When valves and or rockers get loose they start to rattle. Before my engine was rebuilt I had that same effect at 4500RPM and above. Valves needed adjusting basically.

Edited March 19, 201015 yr by WingZr0

I came across this thread and thought of this discussion.

http://www.classiczcars.com/forums/showthread.php?t=36331

Not sure if the problem is related but there is some good advice in the thread that might give you a fresh perspective.

I have check many of the things mentioned in the link you posted. Thanks a lot though. The noise does not occur when the engine is cold though if that helps anyone eliminate anything, it only occurs at or near operating temp.

Jan

Hey guys.

I know this is old post but here's a bit of an odd update. Sunday I decided to clean and wax the Z. In the process I found that I have a can of Seafoam in the car. Decided, hell why not clean the motor too. Poured a third of the bottle in the motor and let it sit for a bit. Started her up and saw just a tad bit of white smoke. (let it sit of about 5 min).

To my amazement I come out this morning (when its like 85 degrees) and take the Z for a drive. No noise, nothing, nadda, it's gone. It was there the night before when I poured the seafoam in. Today it did it twice in a 20 minute drive. (for reference it used to do it all the time, anytime I revved the motor on the way down it would rattle). Any ideas? Could it be a stuck valve or something?

Jan

Hey guys.

I know this is old post but here's a bit of an odd update. Sunday I decided to clean and wax the Z. In the process I found that I have a can of Seafoam in the car. Decided, hell why not clean the motor too. Poured a third of the bottle in the motor and let it sit for a bit. Started her up and saw just a tad bit of white smoke. (let it sit of about 5 min).

To my amazement I come out this morning (when its like 85 degrees) and take the Z for a drive. No noise, nothing, nadda, it's gone. It was there the night before when I poured the seafoam in. Today it did it twice in a 20 minute drive. (for reference it used to do it all the time, anytime I revved the motor on the way down it would rattle). Any ideas? Could it be a stuck valve or something?

Jan

Maybe the can of Seafoam was rattling when you revved the motor.

I have actually spent a few moments in the past wondering what "that noise" was from the rear end of the car then realized it was the old beat up speakers behind the seats sliding back and forth...