New noise from a new engine

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Well, it's not the TC bolts. They're all tight with no witness marks. Don't see any marks inside the distributor cap. Riser valve has been removed from the manifold. So now I'm leaning back toward an exhaust leak.

I'm a rookie engine builder, and I'm thinking maybe here's my mistake. I read that these 340 manifolds didn't use gaskets, but had the heads and manifolds machined flat for sealing. I didn't do that, and instead added a smear of copper RTV to the mating surfaces. A slight leak could explain why it took a few miles for the noise to appear, and it's varying intensity. Sometimes I can't hear it at all. Could be that I just need a good set of gaskets as Icetech suggests. What are those, anyway?
 
I used Remflex exhst gaskets on my 340. It's a long shot, but take dist cap off and rollover by hand, see if rotor is hitting the pickup? I had a new dist pickup that was fd up.
Does sound vary with rpm?
 
6T9QDA said:
Well, it's not the TC bolts. They're all tight with no witness marks. Don't see any marks inside the distributor cap. Riser valve has been removed from the manifold. So now I'm leaning back toward an exhaust leak.

I'm a rookie engine builder, and I'm thinking maybe here's my mistake. I read that these 340 manifolds didn't use gaskets, but had the heads and manifolds machined flat for sealing. I didn't do that, and instead added a smear of copper RTV to the mating surfaces. A slight leak could explain why it took a few miles for the noise to appear, and it's varying intensity. Sometimes I can't hear it at all. Could be that I just need a good set of gaskets as Icetech suggests. What are those, anyway?
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Since they come with gaskets from the factory and I have never read anywhere that 340 exhaust manifolds don't require gaskets, throw that article out.
 
Plug the exhaust to create back-pressure, hold cloths over the tailpipes, apply pressure, listen for leaks, - not rocket science.
 
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Post #15. If the reluctor contacts the magnet, you get NO spark & you would soon know because the engine will run rough & likely misfire.
 
Mean416 said:
It's always an exhaust leak right? Really.... it's not a Mopar if it doesn't have an exhaust leak or two snicking away
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Exhaust cut outs in the system fix that. No longer will you hear that darn tic, tic
 
I have run Flat out Graphite gaskets and remflex. Both worked fine.
 
I
A56 said:
Since they come with gaskets from the factory and I have never read anywhere that 340 exhaust manifolds don't require gaskets, throw that article out.
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I must of read the same article, because I read the same thing, years ago. I never bought a new 340 car, so I'm not sure if that is correct. All the 340's I have played with had a gasket of some sort. My thinking here is, if I recall correctly, you say you rebuilt a 318. It appears you may have 340 exhaust manifolds on it. The manifolds ports are larger than the 318 heads, so maybe you are not getting a good seat. Another view is, did you use a 340 head ( X,J,O, or U) on a 318 exhaust manifold? If so you will have a opening on the bottom of the manifold and exhaust will escape there. You will need a 340, 360 or headers, if so. I believe the 360 head will be the same issue.
 
I'm using early 340 manifolds on '86 318 heads, and the air injection holes below the exhaust ports have been plugged.

A stethescope didn't tell me anything conclusive externally, neither did pressurizing the exhaust pipe. The noise still varies in intensity and at times sounds more metallic, making me think about a failing lifter. They're the original hydraulic rollers. I'm going to remove the valve cover(s) and check for loose pushrods, as well as probe further with the steth.
 
Y
6T9QDA said:
Well, it's not the TC bolts. They're all tight with no witness marks. Don't see any marks inside the distributor cap. Riser valve has been removed from the manifold. So now I'm leaning back toward an exhaust leak.

I'm a rookie engine builder, and I'm thinking maybe here's my mistake. I read that these 340 manifolds didn't use gaskets, but had the heads and manifolds machined flat for sealing. I didn't do that, and instead added a smear of copper RTV to the mating surfaces. A slight leak could explain why it took a few miles for the noise to appear, and it's varying intensity. Sometimes I can't hear it at all. Could be that I just need a good set of gaskets as Icetech suggests. What are those, anyway?
Click to expand...
You say you removed the heat riser value from the right manifold. Did you plug the two holes from the rotating value?
 
I took a short video, but the sound doesn’t come through well enough to be useful. It seems a little worse, with more of a clattering quality to it, so I’m going to have to go in. I’ll post when I get a look at the innards.
 
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