4.3L noise. this is driving me nuts!!!!

Hello and thanks for taking the time to look at this.
OK i'm at my wits end on this one.
I have a 1995 chevrolet G20 van. It's equiped with a 4.3L TBI V-6. I
have a knock in the engine that shows up after its warmed up. If i were to describe it, it sounds just like a lifter. I have replaced the lifters ( very $pricey$ i might add, its a roller lifter engine ) with no luck. This engine is equiped with the counter balancer by the way. After doing that, i removed the inspection plate from the transmission, unbolted the torque converter and slid it back out of the way. I fired the engine up and the noise was still there. Next i removed the serpentine belt and fired the engine up and the noise remanined. Fustrated i searched the internet and i came across a GM Technical Service Bulletin that said the exaust valve seals might be starving the guides for oil causing the valves to bind. I went and purchased the updated seals from GM, installed them, and noted no change. I have eleminated exaust leaks and catalytic converter noise.
The source of the knock seems like it is coming from the center of the engine. I placed my stethoscope on the timing chain cover and i can hear it. I have heard tales that the noise may be caused by slack between the counter balancer and camshaft gears and supposedly GM knows about this. If i put the engine under a heavy load (pressing the gas while my foot is on the brake), the noise goes away. I have tried changing weights of oil from 5w30 to 50w racing oil to get this engine to shut up. You dont really hear it running down the highway but if you let of the gas, you will hear it for a bit.
Its not a deep knock like a rod or a main and like i said earlier it shows up after the engine is warmed up. The engine runs great, very smooth, has good oil pressure, produces good power throughout the RPM range and it only has 60,000 miles on it. The engine has been treated to regular oil changes. Please help before i have to drop the engine out of this thing!
Thanks in advance!
PMB
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pbrady73 wrote:

I had an 88 350 that would knock and it did it for a couple of hundred thousand miles. When I finally tore it down the number1 piston was installed with the arrow to the rear, 200,000 miles and the blue smoke at stop lights got me to tear it down. Have you checked out your harmonic balancer?
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This a very real possibility. I am in the process of pulling the transmission out so i can have it beefed up and while im in there, i will check for a cracked flywheel. If i cant find anything else, then i'm going to drop the engine out of it. Thanks for the suggestion!
dave wrote:

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I am having the same noise in my 91 s10 pickup with a 4.3L v6. It just started a few days ago. Sounds like it is coming from the center of the engine down low. The engine has good oil pressure and has been treated well. I havent looked into it yet but would appreciate it if you could post what you find. thanks

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