I'm having a "valve noise" problem with my 390.
I just recently got the thing running after sitting for about a year.
I installed a new EDL-1411 carb and an EDL-2105 intake manifold. The rest is stock.
During the install, I removed and cleaned each lifter. I also rolled each push rod on a glass surface.
Once bolted back together, under a little throttle it started clacking.
So, using a piece of PVC pipe, I pressed it against each rocker until I tracked the noise down to the #5 cyl. I don't recall if it's the intake or the exhaust, but, it's the second rocker (from the front) that's making the noise.
I couldn't seem to pull the lifter out from between the intake and the head, so, I had to remove the intake again and replace that lifter with a new one.
The clatter remains....(?)
In addition to the clatter, if I punch the throttle, it will back-fire, as if it's back-firing into the intake.
I can't figure if it's: 1) the cheap 87 octane I'm using,... 2) a valve problem (burnt or chipped)... or 3) something else.
I could see nothing wrong with the rocker-arm shaft...
The new carb/intake seems to be working fine and I replaced the vacuum advance, as it *was* defective.
Any ideas...?
Thanks,
steve

 

I think its pinging. Check your timing with the vacuum hose that goes to the distributor pulled and plugged. It should be around 10 degrees BTDC.

 

Does this noise happen at idle? How did you determine that it was #5?

-Scouder

 

Could Be Bad Cam. Cam Lobes Wear And Round Off ,causing Valve Not To Open Fully. If Exxaust Valve , Exaust Back Up And Causes Poping Or Back Fire Out Carb.

 

I've got a mysterious noise in my motor that sounds VERY similar to yours. I always thought it was my valvetrain (and may still be) but I replaced/ checked lifters, pushrods, rocker shafts, rocker arms, checked torque, made sure I had the odd oil bolt on number 3 and 6 rocker arms, checked for oil pump pumping with a cut up valve cover. Seemed to be pumping fine, just the normal lame dribble of oil out of the top of them. AND I STILL HAVEN'T FOUND THE PROBLEM EITHER! I found that some of it was my fuel pump and it went away when I replaced my fuel pump, but now it's back again.... It's loud enough I can hear it at idle and mostly at 2000rpm-ish. I still swear it's in my valvetrain, lets find this problem we're having because it's driving me crazy!

 

Exhaust leak maybe?

 

Mine's good Rusty, I couldn't find any header leaks. It's def a tap or a knock coming from up top. I wonder if it's inside of one of my heads... Mine seems to get worse as the motor warms up.

 

Hrm. Now do you have the adjustable valvetrain on that? If so, pop the valve covers off and check for loose adjuster screws. It should take at least 7 ft-lbs to turn 'em. Also check for loose pushrods. I'd go through the firing order and reset the lifter preload, and see if it goes away.

 

Rusty,
I checked the timing,...it was a little high, so I set it to around 9 BTDC.

Scouder,
Only faintly, in back ground. I removed the VC and held a piece of PVC pipe (used as a stethiscope...sp?) up to each rocker to hear the sound it made. The right-side rocker of #5 made a definite "clack-clack" sound, even at idle, compared to all others.

**Update: (since original posting,...)
I added a pint of octane booster to a half tank and topped off with 91 octane and put a hundred miles on it. Much of the top end noise has cleared up considerably, but, there is still this persistant "clacking" noise under any degree of throttle. I don't hear it under idle,...only on the road.
#5 rocker has quieted down, too. So, I don't think it's any longer the source of the noise.
Rusty,
Using my piece of PVC pipe, I began listening along the edges of the exhaust manifolds. I Located a small leak coming from #3 exhaust port at the manifold. With all the background noise I could barely hear it without the pipe.

I just finished pulling the exhaust manifold and it does show signs of an exhaust leak.
The odd thing is, this is a brand new manifold gasket.
Tomorrow morning I will put on a new gasket and see what it sounds like.

ceetwarrior,
hope this all helps.

Thanks,
steve

 

Steve, how would octane help the noise? That's funky.

Rusty, no adjustables for me, just old non-adjustables.

I have a mechanics stethoscope I wonder if I should try that to find my problem. I guess I can't worry about it much, this weeknd I'm swapping in my NV4500 5-speed... eek!

 

What did you torque the rocker bolts down to? Believe 40 lbs is the right torque on those bolts.

 

45lbs for me....

 

ceetwarrior:
I'm not absolutely sure just how much noise is generated by pre-detonation, but, from the archived posts I've read and here, the indication is that low octane fuel will produce top-end noise that sounds like a bad valve train.
Previously, I thought it just caused dieseling when you shut the engine off. I didn't know about the top-end noise too.
I haven't owned a V8 in 20 plus years. Back then, leaded gas eliminated knock and ping. Those are things I've only heard of up to now. (Hmm... can I just drop some lead fishing weights into my gas tank,...?)
Update:
I slapped a new exhaust manifold gasket on and lit her up. After it warmed up, I re-torqued the manifold bolts. No more *odd* sound coming from that part of the engine. In fact, it was pretty darn quiet.
I then took out my trusty, 3ft. piece of 1/2-inch PVC pipe and did a sweep of the entire top end again, at idled. I detected a very slight "chuh-chuh-chuh" sound coming from the manifold gasket around #7 cyl. exhaust port. Over the fan noise, I could hear none of this, without the PVC pipe.
I took it for a spin and sure enough, under a little throttle, there was a small "clacking" sound coming from the drivers side of the engine. Sounded just like a noisy lifter or rocker, except I'm pretty sure it's an exhaust leak !!!
steve

 

Just studied up on pre-ignition and detonation (there is no such thing as pre-detonation) - the best article I found was:
http://www.streetrodstuff.com/Articl...tion/index.php

Your engine can handle a lot of detonation, but pre-ignition almost always melts your piston before you even know it is happening. I recomend reading what this guy has to say -

 

I stand corrected !
I mis-spoke when I wrote pre-detonation, when I meant pre-ignition. I'm new to all this terminology.