Sudden engine knock after overheating?

1992 PONTIAC FIREBIRD
111,000 MILES • 5.0L • V8 • 2WD • AUTOMATIC
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RANDALL PAINTER
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Recently purchased this vehicle and got it running. It's been good for two weeks then yesterday on my way home it started overheating. I pulled it over, let it cool down and added some more water. Got it the rest of the way home. Changed the thermostat, drained and flushed the cooling system. Took it out again and it seemed fine for a while, then it started sounding like the belt was slipping and had a knocking sound. Got it back home and changed the water pump and took off the smog pump. The smog pump was going out and making a screeching sound but there was still a loud knocking on the driver's side of the motor.
Feb 5, 2024 at 1:25 PM
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RANDALL PAINTER
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Here's a video of the sound https://www.tiktok.com/t/ZT8v1skV1/
Feb 5, 2024 at 1:57 PM
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STRAILER
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That is a bummer, but it sounds like a rod bearing has spun but to be sure let's remove the valve cover on the driver's side to look for a broken valve spring or bend push rod. Thanks for the video, you can upload the video in your replies in the future or if you have a question about what you find once the valve cover is off.
Feb 5, 2024 at 5:31 PM
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RANDALL PAINTER
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That's kind of what I was thinking, too. I need to pull the covers to get them cleaned up and repainted anyway, so I'll check back in with what I find, shortly.
Feb 5, 2024 at 7:38 PM
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RANDALL PAINTER
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Everything under the valve cover looks in order to me. No loose rockers or broken springs. The only thing that struck me as odd was the lack of oil pooled around the springs...
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Feb 5, 2024 at 11:55 PM
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RANDALL PAINTER
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This just dawned on me. Could it be the oil pump? I only say that because under the valve cover was suspiciously dry and my oil pressure gauge was fluctuating quite a bit, now that I think about it.
Feb 6, 2024 at 4:31 AM
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STRAILER
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Thanks for the video. The valve springs look okay, the oil pressure will fluctuate when a rod bearing has spun which sounds like what has happened, the engine needs to be removed and the engine disassembled to confirm the issue.
Feb 6, 2024 at 10:30 AM
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RANDALL PAINTER
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Thought I'd post an update. It was 100% the bearings. See pics xD
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Feb 9, 2024 at 4:33 PM
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STRAILER
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lol, yep, that will do it, thanks for getting back to us :) Also, let me know if you need any more help getting the car back on the road.
Feb 10, 2024 at 10:40 AM