99 corvette - rod knock?
Tech Contributor
Joined: Dec 2006
Posts: 10,962
Likes: 29
From: Van Buren Arkansas
Wounded Warrior Escort '11
A failed lifter will sound like loud tapping but it will sound like the top middle center of the engine. A bad rod will sound deep and a more serious knock sound...for the lack of a better description. I had a failed lifter on my '99 as well and when it finally went, it was pretty loud. This wasn't till 274k miles though. How many miles on your car?
Melting Slicks
Joined: Jun 2002
Posts: 2,246
Likes: 66
From: Middletown CT
Does the noise go away when the engine warms up? If so it may be a "nonproblem" found in many LS1s. The bottom of the piston can contact the cylinder wall causing the knocking noise. As the piston warms up, it expands and seats properly in the cylinder. Mine does it on a cold day, but goes away in a minute or two. GM assures us that while it is a "pleasureability" issue, (their words, not mine) it is not a problem that has to be addressed. I think the later years had coated pistons to eliminate or reduce the noise.
Read about it here:
http://pistonslap.com/
Read about it here:
http://pistonslap.com/
Last edited by Greg_E; Oct 10, 2011 at 08:46 PM.
