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Would a rod or bearing knock go away when warm ?

Old 07-21-2009, 10:06 AM
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Question Would a rod or bearing knock go away when warm ?

I have this noise on my ' 99 SS w/ 103K - this started around roughly 67K or so.

If you are under the hood when the motor is cold and manually operate the throttle linkage you can hear a knocking sound that definitely increases with engine speed.

The sound is also noticeable while driving .

It will disappear after driving for about 15 minutes , but not necessarily after normal operating temps are reached.

Oil pressure is still good, and no more than normal oil burning is occuring.

The car was broken in on dino oil - I am the second owner ( since 24K ) and have run synthetic for all but about 3 oil changes.

I searched, but have not really found anything that would appear to cover this.

I am not terribly concerned about it as I know at least 2 other people that have had 5.3's in Z71's w/ the same noise, and one of them ran for over 150K before the truck was traded in.

What I would like to know is if anyone can ID what it is making that noise !

Thanks !

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Old 07-21-2009, 11:18 AM
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LSx engines have a very noisy valvetrain, if it was rod knock it wouldn't have ran for 50k miles I know the exact noise you're talking about because i also had the same issue before i did my heads and cam swap, the noise is now gone my car had 11k miles when i purchased it and the noise was there, i did the swap at 65k so i had the tapping for a while.
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Old 07-21-2009, 01:07 PM
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Probably just the noisy LS1 valvetrain.

If it sounds serious, but seems to go away as you drive it, it could be a bad lifter.

Rod knock doesn't cure itself. Ask me how I know.
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Old 07-21-2009, 01:40 PM
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Piston slap?
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Old 07-21-2009, 04:38 PM
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What im thinkin ^
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Old 07-21-2009, 06:10 PM
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sounds like a noisy lifter to me. my lsx motor does the same thing on cold starts. a rod knock isnt really noticeable till the motor warms up. and varys with rpm. has a sbc with that problem.
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Old 07-21-2009, 08:25 PM
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Originally Posted by JakeRobb View Post
Piston slap?
+1 he is right

it stops b/c the pistons and the Cylinder walls expand and makes up for the wear
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Old 07-22-2009, 01:27 PM
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It is most likely piston slap....mine has done it since it was now has 190,000+ miles on it....after I let it idle for about a minute or two it goes away...
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