engine rattle

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Erik - 27 Oct 2005 22:52 GMT

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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Backyard Mechanic - 27 Oct 2005 23:02 GMT

> 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.

uh, no... dunno where you heard that... loose mains are noisy under no
load

> Could it be the pistons?

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

> I know the cilinders are worn but compression
> is still ok (low but ok).
> Any thoughts?

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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Kruse - 28 Oct 2005 03:42 GMT

> My engine 66 289, has a loud rattle/knock at low rpm.
> As soon as the engine is under load the rattle is gone.
[quoted text clipped - 5 lines]
> Thanks,
> Erik.

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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Scott Van Nest - 28 Oct 2005 19:29 GMT

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

> My engine 66 289, has a loud rattle/knock at low rpm.
> As soon as the engine is under load the rattle is gone.
[quoted text clipped - 6 lines]
> Thanks,
> Erik.

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