Knock diagnosis
Thread Starter
Instructor
Joined: Apr 2022
Posts: 110
Likes: 7
From: Austin Texas
Knock diagnosis
Curious on opinions regarding this noise. I bought the car a year ago and it had it very slightly but it has gotten more aggressive over the past year. Had 105k when purchased now 110k. Isn’t my daily. Noise nearly completely goes away after warming up for about 10 minutes and driving a little bit afterwards.
sounds lower end than higher. No performance issues. Good oil pressure with no leaks. New oil pans, new oil pump o ring. New ATI harmonic balancer. Did an engine flush and changed oil brands, currently pennzoil platinum 5w30. Still doing it. Currently has Corsa xtreme catbacks, k&n cold air intake. Running 93 through her always.
not aggressive enough to be a rod. Plus it goes away after warm. Doesn’t sound like push rods. Doesn’t sound like lifters, and too low to be really, but maybe it is?... Rocker arms checked out good. Doesn’t sound like exhaust leak to me but haven’t fully checked yet. No metal in oil or filter.. no check engine lights, she’s running mean.. but this noise is driving me crazy plus kind of embarrassing lol.
The only conclusion I can come to is a bad piston slap as I know these are notorious for them 🤷🏻♂️
https://youtu.be/C-CFQRn6csg
sounds lower end than higher. No performance issues. Good oil pressure with no leaks. New oil pans, new oil pump o ring. New ATI harmonic balancer. Did an engine flush and changed oil brands, currently pennzoil platinum 5w30. Still doing it. Currently has Corsa xtreme catbacks, k&n cold air intake. Running 93 through her always.
not aggressive enough to be a rod. Plus it goes away after warm. Doesn’t sound like push rods. Doesn’t sound like lifters, and too low to be really, but maybe it is?... Rocker arms checked out good. Doesn’t sound like exhaust leak to me but haven’t fully checked yet. No metal in oil or filter.. no check engine lights, she’s running mean.. but this noise is driving me crazy plus kind of embarrassing lol.
The only conclusion I can come to is a bad piston slap as I know these are notorious for them 🤷🏻♂️
https://youtu.be/C-CFQRn6csg
Last edited by lspowah; Feb 17, 2023 at 01:33 AM.
Race Director
Joined: Oct 2004
Posts: 12,861
Likes: 4,664
Wish I could help. I have a similar sound, though it doesn't do this when cold, at idle. But it does do it when cold if revved to 2,000 rpm. After about 10 minutes, it's gone. In your motor, I suspect the valvetrain. Either a lifter, cam lobe, or rocker arm trunnion. What's strange on yours is it seems to disappear when you give it some rpm, like more oil pressure helps. For that reason, I'm going with a bad lifter. But hey-I've never found mine. Heads been off twice, and 2 sets of lifters, still does it, 43,000 miles, so it can't be life or death. Motor runs great. Wish I could offer more help.....
Tech Contributor
Joined: Oct 1999
Posts: 41,040
Likes: 9,801
From: Charlotte, NC (formerly Endicott, NY)
This is a sample of LS6 piston slap that I recorded back in 2011. This is a buddy's 02 LS6 and my 97 LS1 and 03 LS6 did the same. On cold mornings at the Glen you could listen to the Corvette engines tapping as the owners warmed the oil before heading out on track. The tapping would fade away about the time the OIL Temperature hit 110 degrees. Nothing to worry about most of them did it with no reduction in reliability. The engine recorded here went another 6 years and many more wide-open throttle track miles before it blew. At the time of the video, the engine had over 30K track miles on it.
Here is a link to an article about LS engine piston slap:
https://auto.jepistons.com/blog/what...ap-false-knock
Bill
Here is a link to an article about LS engine piston slap:
https://auto.jepistons.com/blog/what...ap-false-knock
Bill
Thread Starter
Instructor
Joined: Apr 2022
Posts: 110
Likes: 7
From: Austin Texas
Wish I could help. I have a similar sound, though it doesn't do this when cold, at idle. But it does do it when cold if revved to 2,000 rpm. After about 10 minutes, it's gone. In your motor, I suspect the valvetrain. Either a lifter, cam lobe, or rocker arm trunnion. What's strange on yours is it seems to disappear when you give it some rpm, like more oil pressure helps. For that reason, I'm going with a bad lifter. But hey-I've never found mine. Heads been off twice, and 2 sets of lifters, still does it, 43,000 miles, so it can't be life or death. Motor runs great. Wish I could offer more help.....
Thread Starter
Instructor
Joined: Apr 2022
Posts: 110
Likes: 7
From: Austin Texas
This is a sample of LS6 piston slap that I recorded back in 2011. This is a buddy's 02 LS6 and my 97 LS1 and 03 LS6 did the same. On cold mornings at the Glen you could listen to the Corvette engines tapping as the owners warmed the oil before heading out on track. The tapping would fade away about the time the OIL Temperature hit 110 degrees. Nothing to worry about most of them did it with no reduction in reliability. The engine recorded here went another 6 years and many more wide-open throttle track miles before it blew. At the time of the video, the engine had over 30K track miles on it.
https://www.youtube.com/watch?v=xdcbZSi04Dg
Here is a link to an article about LS engine piston slap:
https://auto.jepistons.com/blog/what...ap-false-knock
Bill
https://www.youtube.com/watch?v=xdcbZSi04Dg
Here is a link to an article about LS engine piston slap:
https://auto.jepistons.com/blog/what...ap-false-knock
Bill
Last edited by lspowah; Feb 18, 2023 at 04:25 AM.
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