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Discussion Starter #1
So, I've got this noise I'm trying to diagnose. It's actually not that noticeable unless you're next to a wall or in the garage where the sound can bounce around. Listening from under the hood you almost can't hear it at the top end is quiet. I stuck my phone under the car and here's what it sounds like. It sounds a lot louder in the video than standing next to the car, which sounds like a soft/quiet ticking.

Seems to be coming from the rear of the engine. Engine runs great, no vibes. Haven't hooked an oil pressure gauge up yet, the oil pressure light never comes on with the engine running unless I just changed the oil.

Ideas? Flex plate? Piston slap? Next on my list is to pull a plug one at a time and see if it goes away

 

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Discussion Starter #2
Also, it's not something you car hear or feel inside the car with the windows rolled up and rolled down you can only hear it if stopped next to a wall or car. Can't feel anything if I touch the bellhousing or the valve covers.

Apparently the engine was rebuilt 10 years and ~5000 miles or so ago and I don't have any of the specifics other than it sounded like the owner before the one I bought was told it was bored/stroked to 347, among other things, but it seems to be a relatively stock long block; 302 4V heads, rail rockers, hydraulic lifters (Not sure if they're flat tappet or if it's a roller cam, but would assume flat tappet), stock exhaust manifolds. Only mods I know of are the Edelbrock intake and carb, which were on it when I bought it, and the Pertronix II I recently installed.
 

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I'd put a big wrench on the bolt in the balancer and turn the engine by hand in both directions and see if you hear/feel a clunk when you do it. If nothing shows up obvious, then key in on the exhaust. Look at the manifold, and all the attaching bolts and then go to the head pipes downstream of the exhaust manifolds. Exhaust leaks are common and make us crazy and think the worst FIRST like internal engine damage. Next check your torque convertor bolts. Let us know what you find.

Kevin
 

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Discussion Starter #4
Thanks for the tips. I guess now I feel less concerned and more annoyed.

No clunk when turning the crank either direction.
Exhaust is fine, no loose bolts, no leaks.
Pulled the access cover and checked the T/C bolts, all tight and no signs of anything rubbing/hitting anything

Using a screwdriver as a cheap stethoscope, I listened to the starter, rear of the oil pan, etc. The ONLY place I could get a clear read of the sound was from the bellhousing and *slightly* when listening to both side of the exhaust, but it was definitely the loudest and most clear on the bellhousing and it wasn't *that* loud. Pulled the plugs one at a time and no change.

Listening to the pan at the shallowest point probably isn't a good read because the oil is going to filter the sound, but I'd think the starter would transmit the sound pretty good if it were something in the engine. It was virtually silent and everything sounded smooth.

Also listened to the trans housing and didn't hear much of anything, oddly the only place I got a decent read on the sound was from the bellhousing.
 

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That sure sounds like an exhaust tic to my ear. Does it go away once the engine warms up? I had a similar sounding knock that I presumed (incorrectly) was rod bearings and it turned out to be the torque converter or flex plate. I know that was the issue because it disappeared after swapping in a t5.
 

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Discussion Starter #6
That sounds like an exhaust tic to my ear. Does it go away once the engine warms up?
Nope, in fact I'd say it's more noticeable after the engine warms up. I need to check again once it's cooled off and kick the high-idle off as well.

I thought maybe it didn't like the Mobil 1 10w30 I put in, so I drained it and put in Rotella T6 5w40 (I love this oil, I use it in my Ram as well and read nothing but good things from people that have run it in their gas engines and do UOA) and no change.
 

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Discussion Starter #7
Here's another video listening from multiple angles (Ignore the messy garage :D). Honestly, the noise is more pronounced in the video than listening there with my own ears and I don't know why, maybe the mic on the phone or the video compression is making it stand out.

 

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This amateur thinks it sounds like an exhaust leak. My '67 suffers from the same noise!
 

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Discussion Starter #9
Well, I did some more shadetree diagnosis using a wooden broomstick, using that method the noise is actually the loudest when I'm listening to the valve cover bolt right by the #8 spark plug. Can hear it listening to the exhaust manifold as well, but it's definitely more pronounced at the valve cover bolt and using the broomstick to listen to the bellhousing I'm not getting anything, really. So it sounds like something with the #8 cylinder or something in that vicinity.
 

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It reminds me of piston slap or a cracked piston skirt.
Could also be a cracked or loose flexplate.
Difficult to diagnose over the iNtrAweBb :D
 

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You mention the pull a plug wire at a time diagnostic, I think that is a good thing to do. What is the history on the engine, rebuilt? Bored or not? Cast or forged or hypereutectic pistons? Turned crank or not? Tell us all you know and try the plug wire diagnostic.

Regards,

Bob
 

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Discussion Starter #12
Well, someone (joker that rebuilt the engine before I bought the car) played a cruel joke on me.

There were no exhaust manifold gaskets installed. Period! Tonight's projects involved:

Replace (ha!) exhaust manifold gaskets
Replace intake manifold gaskets (There was a slow oil leak at the rear of the intake manifold that was annoying me)
Replace coil (I was still getting a misfire idling in drive and off-idle in park, the coil looked well aged so I wanted to make sure my entire ignition system was up to snuff)
Replace Autolite AP45 platinum plugs with NGK V-Power copper plugs (Likely the cause of the strange misfire based on what others have said about plats)

So far it seems like the general consensus was correct, the tick/knock was an exhaust leak. I'm going to drive it tomorrow and see how it does in general, I only had a chance to run it and make sure the coolant was bled, but so far it seems to be running smoother, starting easier, and I'm pretty sure the tick/knock is gone.

I'll follow up tomorrow with a new video for comparison (and by tomorrow I mean Thursday, which is technically today).
 

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What! your supposed to use gaskets?:toung: It's amazing how much noise the manifolds make when the slightest gap/crack exists....
 

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...Replace Autolite AP45 platinum plugs with NGK V-Power copper plugs (Likely the cause of the strange misfire based on what others have said about plats)...
What others? And what have they said? I would be interested to know as I am running the plugs you mention and they seem just fine to me.

Regards,

Bob
 

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Discussion Starter #15
Here's the engine after installing the gaskets. Going to re-torque them after the engine cools, but I'd say the knock is mostly gone now.

 

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Discussion Starter #16
What others? And what have they said? I would be interested to know as I am running the plugs you mention and they seem just fine to me.

Regards,

Bob
Seems to be hit and miss (No pun intended), the plats seem to be more sensitive to less-than-ideal conditions. I still have a random misfire off-idle from about 1800rpm up. Happens every 1-2 seconds but isn't like clockwork.

However, part of another issue I had is now gone. After driving and then letting the car sit for 10-15 minutes it takes a good 4-5 seconds for the engine to fire and with the AP45s it would stumble and act like it wanted to die for about a minute after restart unless I drove it. With the NGKs I still have the long start, but once the engine fires up it runs smooth, no stumbling or anything. Fires right up after just shutting it off and also fires right up with the first start of the day, it's just those in-between starts that are the issue. Only thing I can figure is heat causing something with the carb and fuel is trickling into the intake causing a temporary flooded condition. The carb itself has been rebuilt, no leaks as far as I can see.
 

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Discussion Starter #18
Pull your dipstick and see if the oil smells like fuel.
I'll have to put some more miles on it, I just replaced the oil the other day. Prior to changing the oil I did smell it a couple of times and I'd say there may have been a faint smell of gasoline, but not enough to say for sure. I know it's not draining the bowl, the engine fires right up in the morning with a 1/4 pedal press to set the choke, high-idle, and squirt some gas.

The carb vents are working fine as well. I do smell gas if I pop the hood after it's been sitting for 15 minutes or so.

Some other info on the fuel system:

Mechanical fuel pump with a stainless hard line running from the pump up the front of the block and along where the head a valve cover meet. There's an in-line Earl's fuel filter there, then the line runs up, behind and around the carb, and into the carb inlet on the passenger side. I'm wondering if maybe the proximity of the line to the block/heads is causing the fuel to heat up and boil a little, causing pressure in the line and push gas past the float seats, causing the bowl to overflow or allow it to escape via the secondaries (Edelbrock 1406 carb - 600cfm w/ electric choke). Maybe? I'm running out of ideas. :)
 
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