engine rattle

My engine 66 289, has a loud rattle/knock at low rpm. As soon as the engine is under load the rattle is gone. My first guess was crank/rod bearings, but I understand they should be noisy
under load and not at idle. Could it be the pistons? I know the cilinders are worn but compression is still ok (low but ok). Any thoughts?
Thanks, Erik.
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uh, no... dunno where you heard that... loose mains are noisy under no load

Yeah.. it COULD be 'piston slap' but that engine isnt known for that tendency.

Does it really matter?
You need to tear it down anyway, whatever it is. Run 20w-50 if it quiets down, then you know.
But like I say, whatever it is, it needs rebuilt unless you want to chance losing that block.
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Erik wrote:

It's PROBABLY engine related, but if your car is an automatic, check the flexplate. (flywheel) Using a long screwdriver or prybar, check each spoke to make sure there are no cracks or breakage. Lots of engines have been sold to customers because the mechanic didn't check this first and was too embaressed to admit his mistake later. If you have a manual tranny, this is not the cause.
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My '71 302 had very similar knock. I tore my motor down (it was on the list anyways) we decided that the timing chain had seen better days. This was back when I posted the question about the plastic covered timing gear. I found all sorts of broken plastic pieces in the oil pan.
Scott

noisy
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