Awful knock at high rpm

2006 PONTIAC G6
125,000 MILES • 3.4L • V6 • 2WD
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MARY RICHARDS
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This car runs good except a knock that is worst at high rpm's. My friend thought it was a cracked flex-plate because it is not a rod knock but the plate looks fine. He says it is coming from the bottom of the engine. Any suggestions?
Jun 10, 2019 at 11:29 PM
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ASEMASTER6371
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Good morning,

Can you upload a video of the noise so I can hear it?

It is either a rod bearing or main bearing from your description.

https://www.2carpros.com/articles/engine-noises

A flex plate would sound like a valve tap.

Roy
Jun 11, 2019 at 4:22 AM
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PATENTED_REPAIR_PRO
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Main bearings don't usually knock but rod bearings do. Drop the oil pan and plasti-gage all the rod bearings.
Jun 11, 2019 at 5:00 AM
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MARY RICHARDS
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What does plasti-gage mean?
Jun 11, 2019 at 5:22 AM
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ASEMASTER6371
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That is when the clearance is checked between the bearing and the crankshaft.

Roy
Jun 11, 2019 at 5:28 AM
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MARY RICHARDS
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Thank you.
Jun 11, 2019 at 5:58 AM
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ASEMASTER6371
  • ✓ASE Certified Mechanic
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  • ASE Certified Mechanic
You are welcome.

We are always glad to help.

Roy
Jun 11, 2019 at 6:04 AM
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PATENTED_REPAIR_PRO
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To use plasti-gage, clean the motor oil off a rod bearing in the connecting rod end cap, lay across the bearing 1 string of the plasti-gage, then install the bearing and cap, torque it down to spec, then remove the bearing cap and measure how much the plasti-gage string got smashed and that tells you the amount of oil clearance and if it's too much, it means the bearing is worn.
Here is another source for how to use it: https://www.plastigaugeusa.com/how.html
Jun 12, 2019 at 4:12 AM
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