So I picked up a 91 FC that had been sitting for a few years, after getting all the crap cleaned out and finally running I come to hear this noise. My thought after some poking around is the chain for the cas on the oil pump, thoughts? The noise is really only at idle, when free revving the noise goes away which makes me think its the slop in the chain at low rpms is the noise. P.S. the water pump/Alt was not hooked up for this short video.
https://photos.app.goo.gl/9Pkatw4LHz4FosR19

 

Update, replaced the chain(which had a ton of play) and the noise is still there, motors starts right up and doesn't smoke. Car revs freely without any hesitation.

 

How does the engine sound with an air filter on it? That is a strange sound to he honest. Have you checked the exhaust heat shields to ensure none are loose? Its hard to hear in the video to be certain if its a whistling or ringing noise..

 

it sounds like rod knock(but goes away when you rev it), the video doesn't really show it. But exhaust mani(beat racing) and exhaust are all tight. Sounds like it's coming from the front of the motor, but nothing is loose on the motor.

 

well, since i have no experience with them going bad, does anyone know what bad thrust bearings sound like?

 

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When I heard it (at least, I think I did), that was my first thought as well, but I'm at most maybe 30%.

 

If he replaced the timing chain, I wonder if he replaced the thrust washers and plates.

 

I didn't, i though I'm slapping my head now wishing I would have looked at them lol

 

 

Good luck, and congrats on your 7

 

How much run time would you need on fresh oil to find bearing material?

 

It's literally anyone's guess. But why guess? Go back in and inspect it to confirm or eliminate it.

 

Update, noise is gone after deleting OMP and adding premix. Thinking the front rotor housing wasn't getting any oil causing that noise(no Oil in/on the injector when I pulled it). Car thanked me with low oil pressure(installing aftermarket gauge to confirm) and the alternator bearing decided it was next.