Piston Slap: To lift, slap, or ignore the LS1?

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PistonSlapThumb_Template 2000 corvette
Flickr/Greg Gjerdingen

Mike writes:

Hi, I own a 2000 Corvette and on a cold start up it makes a strange noise. I’m not sure if it is a valve lifter or maybe piston slap? It gets quiet after a few minutes of running. Any suggestions?

Sajeev answers:

You are right for not being sure whether it’s valve lifters or piston slap, because they are both valid diagnoses that are impossible to verify without an engine teardown. As much as I love GM’s GEN-III and newer pushrod engines, these quality niggles do drive me nuts. Still, unlike the well-documented LT4 failures in C7 Z06 Corvettes or “Displacement on Demand” 5.3-liter truck engines, this is an annoyance and nothing more. I downplay the LS1’s issues because there’s little you can do to resolve the noise, and neither potential source shortens the engine’s lifespan.

Piston-slap correction requires complete engine disassembly to install revised piston rings. That would reduce a cold LS1’s more generous tolerances, but there’s no guarantee it solves the problem … which implies such extensive effort is unnecessary!

Lifter replacement requires less labor, but you still gotta yank the heads to reach these components. Again, if we could diagnose the problem, should we even care if, as you report, they do their job satisfactorily once the engine warms up?

Perhaps there’s another reason why this happens, especially if your C5 is a late-2000 build. GM technical service bulletin 02-06-01-038 suggests a defective oil pump O-ring that can add air to the oil. This aerated oil can cause the lifter noise, especially when oil is cold and thick. The fix is cheap in terms of parts, but labor for a tight-fitting Corvette is likely between 4– 5 hours: Spending $600 or more for this exploratory repair seems a bit … blindly optimistic?

My advice is to do nothing and deal with it: Your LS1 doesn’t have GM’s terrible “Displacement on Demand” system and therefore won’t be hurt by the noise, be it lifters or piston rings.

Have a question you’d like answered on Piston Slap? Send your queries to pistonslap@hagerty.com, give us as much detail as possible so we can help! If you need an expedited resolution, make a post on the Hagerty Community!

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