I think the sound comes from the front of the engine. I crawled under the truck while Mrs. Wally gave it some gas (wheels very well blocked!) and the sound was not coming from the throwout bearing.

How does this type of harmonic balancer go bad? It's been on the 261 since 2004. When I increase the RPMs, it doesn't wobble, vibrate, etc. It stays spot on.

Can you replace a harmonic balancer while the engine is in the truck?

Thanks for your help!!

Here's a video with perhaps better sound.

Another Video w/Sound.
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Last edited by Wally / Montana; 07/02/2020 12:54 AM.
1948 3/4-Ton 5-Window Flatbed Chevrolet

34 Years. Now with a '61 261, 848 head, Rochester Monojet carb, SM420 4-speed, 4.10 rear, dual reservoir MC, Bendix up front, 235/85R16 tires, 12-volt w/alternator, electric wipers and a modern radio in the glove box.