noise under mid-hard acceleration 71 340 cuda

[Katfish]

What did you set it to for test?
IMO 36 is way too high, mine detonates at anything above 28

[culp71]

I don't recall off the top of my head, I noted them at home while i did it each one, I tried about 6 different timing settings all back from 36, none of which changed the noise.

I do not know what vacuum @ idle I currently have, I know it powers my brakes sufficiently...

if it turns out to be engine lean related I suppose ill have to take the carb apart and try different jet, rods and metering rod spring, as I don't think I changed the spring from the stock 1406 spring prior.

(stock 340 block bored over 40, forged crank, "stock" valve setup , stock cast heads and rocker setup, w Edelbrock cam and 1406 carb)

I hate to do this as its a shaker car, so really hate having to take all of that off, it was tricky enough adjusting distributor with the shaker in place. but got to figure this out

[Scooter]

What did you set it to for test?
IMO 36 is way too high, mine detonates at anything above 28

Usually 34~36 degrees all in is pretty typical on most street (pump gas) motors. What are you running?

[culp71]

so since it seems a timing change did not affect this noise, could a lean carb issue on the mid-top throttle cause a similar valve (knock, ping, rattle, detonation) noise?

[Solarguy]

An exhaust leak can make a rattling sound especially under acceleration.  I just replaced exhaust manifold that had a crack,  sounded alot like detonation pinging and only occurred under load, not in park or neutural

[Shane Kelley]

So your getting bounced in all different directions. You have established the fan is not hitting the top of the shroud. Usually won't hear that anyway but you have checked so that is done. What's the best way to check for detonation? You start where the tattle tell will be and that's the spark plugs. So you need to pull the plugs and look for tiny fragments that look like shiny specks. You need a hand help micro scope or something similar. You can't see it with the naked eye. Also you can see how your plugs look to see if your lean or rich. Just from what your saying it sounds like detonation but we can only speculate at this point. You also need to put a timing light on the motor and see what total timing is so we can establish a baseline. With the timing light on give it some throttle until you see the mark move to the highest spot and that will be your total timing.  Might be in the 3000-4000 range depending on your distributor. Let's start with these things and then go from there. This microscope is cheap and works great for reading plugs.

https://www.amazon.com/SE-MW10084-LED-Illuminated-Pocket-Microscope/dp/B000OVHVVQ/ref=sr_1_63?crid=3TG2PV82BLHBC&dchild=1&keywords=handheld+microscope&qid=1598359536&sprefix=handhelp+mi%2Caps%2C168&sr=8-63

[mopar jack]

Did you eliminate the torque converter as a source? I have had the inspection covers rattle under load. They can get bent easily and hit the flex plate bolts.

[culp71]

a lot of directions but anything to find this issue, I appreciate all.

"Did you eliminate the torque converter as a source? I have had the inspection covers rattle under load. They can get bent easily and hit the flex plate bolts"

yes I did, early on I had a problem with the torque converter flex plate bolts hitting the back of the original inspection plate. I tried bending it to clear everything I seen hitting it but ended up replacing it with a aftermarket one which seem to be better and cleared everything.
so right after I first had this noise, (a week or so ago) I removed it completely and took a test drive, unfortunately the noise was still there. 

I can also add after a drive last eve that the sound seems to be more on the driver side up under the hood. it also doesn't always seem to be re-creatable in the same manner, I put rubber hoses on all the brake line "spring wraps" with zip ties, bent a PS hard line that looked to be very close to the PS mounting bracket, might have been touching with certain vibrations, added rubber spacers to few other possible areas, but sadly took it on another drive and it still made the noise.

I removed the pass side exhaust manifold and it seem to have a perfect condition no cracks and gasket with no leaks. I put it all back together and it still makes this noise. I will check the driver side manifold this eve.

timing light confirmed around 3200 timing is all in advanced at 35, (10 initial and 24 from mec advance /no vacuum) doesn't exceed this 35 with increased rpms. possible that the mec advance is coming on to much to late or not curved properly? I will pull the plugs and inspect.

[culp71]

I pulled driver side exhaust manifold and it too is perfect, no cracks etc. I thought Id had figured it out as I dug around and found that the warm air door on the bottom front edge of the shaker base would move around a lot, making a lot of rattle metal on metal noise, and free flapping even though it was connected to the shaker cable correctly. it was very loose on the pivot rod and against the surrounding shaker base/flap. it could easily cause the rattling noise. I secured it so it couldn't move, and took it for another drive,  I also changed some linkage, added some spacers as the Trans and throttle linkage was able to move around ( especially the trans linkage) and could have been the source of the noise as well, but the noise still remains.
I will be removing plugs to check for color and particles, fingers crossed that this will not be the case. I really highly doubt it. but running out of options.  it also seems to be more isolated after initial load and acceleration, only after about 2 second then noise goes away, then comes back right before I let off. not constant and not right away when throttle is pressed quickly.

any one have alternator or steering pump make a rattling noise at high rpms?

[Jay Bee]

Back in 2013 I was trying to track down an intermittent metallic rattling sound from my car. I thought for sure it was somewhere from the exhaust, usually went away after the car warmed up. To make a long story short, my thrust bearing wore out to the point where the torque converter/ flex plate bolts were hitting the block. Just wanted to share an elusive noise situation I had and really hope it's not your situation.

I've read that you've checked those but made take a second closer look.

[culp71]

  you guys are the best. 
thanks to ALL of you and all of your help!
I have finally tracked down the noise....it ended up being the timing.
based on your guys first suggestions of a possible timing issue, I had ordered a new dis from summit, as I remembering not being happy with the current dis appearance or fitment anyway, and wanted to have a replacement if this was the case.

Clearly evident now that something in that dis was not right.
It was new 2 years ago and I had set it up initially when completing restoration on the car. set to 25 advanced the 30 then closer to 35, it ran fine, I since have put on around 900 miles and then noticed a new random light rattling noise during the first ever hard acceleration, since I have checked and adjusted the timing at least 50 times. I tried a few timing changes but while sometimes it seem to get rid of it for a while it would always come back from. after trying everything else I could think of I decided to check the timing...yes, again.
So on Friday I checked it a bunch of times in a row, a lot. The timing while usually right on, would spontaneously jump all over the place, up to 40 and even closer to 50 sometimes, (no noise) but way past timing tape marks....but then the very next time it was nuts on with no more then 35. I loosened the hold down and tried to turn back the timing, but dis rotation did not seem to affect timing very much.
I turned it 1/16, then 1/8, then almost 1/4 turn ,first counter clockwise then clock wise with very little or no change in timing...
what the shit I thought?!
I turned everything off. tried again the timing again was again perfect, then all over, then fine.very jumpy and erratic.

Reluctantly I removed the shaker and all that that involves, so I could pull the dis. Figured I'd find a twisted, broken or missing slot tab on the bottom of the shaft. the tab looked fine. I was preparing to take it apart the check weights, springs, shaft etc,..but at this point I was ready to go "office space" on this thing...I was so done with this dis...about 30 second later UPS pulled up and i seen him carrying a summit racing box, hot damn!
I opened the box, dropped in the new dis from summit, put on a temporary air cleaner connected timing light, set the distributor itself to around similar rotation location as prior and turned it over. I had to rotate distributor counter clock wise about 1/6 turn counter clockwise compared to the prior dis, to get it start and run, as soon as i did that it was instantly completely different.

Timing was nice and touchy with dis rotation, I easily set it to around 10 initial, and ran it up, mec advance kicked in super solid and super steady up to around 35, it never jumped around at all or progressed past this point. I then let off throttle and it came down to "idle" but it was around 1500 rpms, it was racing. previously idled around 900, so I turned my idle stop screw about 4 turns out, rpms then came down to around 850 and WOW! does it ever sound different, it now has a that slight thump and that gutsy sound that it never really had before. I had put in a slightly aggressive cam compare to stock, but after getting it done I always wished I went more aggressive as it seemed to be really smooth and not have a thumpy idle i wanted. evidentially this too was all due to that damn distributor.
Now, it has a nice thumpy idle, starts super easily, just barely bump the starter, at idle the thumpy cam rocks the shaker a little and improved throttle response, a ton of power and torque, that thunder-ise gutsy power and grunt,
and best of all no noise of any kind.

I pulled the plugs and find no evidence of any metallic material or damage, thank god.
I put in a new set of plugs so I can really dial in my carb setting now knowing everything else is spot on.

It is a completely different beast now!

while the noise had only happened a few times before, now since the dis change it hasn't happen once.
I drove it Friday for about 2 hours, sat for another 2, then Sunday for about 3.
and I have put the pedal down more times then I ever have collectively in all my cars ever.

With this timing issue behind me and corrected is there anything else I should check or do or be concerned with?

[anlauto]

That's awesome news    What distributor did you buy from Summit ?

[culp71]

it is the Summit Racing® Electronic Mopar Distributors SUM-850003-1
perfect fit and function and looks fairly stock i think, anlauto would know way better. 

https://www.summitracing.com/parts/sum-850003-1

[culp71]

With this timing issue behind me and corrected is there anything else I should do, check or be concerned with?

[anlauto]

it is the Summit Racing® Electronic Mopar Distributors SUM-850003-1
perfect fit and function and looks fairly stock i think, anlauto would know way better. 

https://www.summitracing.com/parts/sum-850003-1

I was just curious, That's the same distributor I've installed in a few cars now