slight knock at start up after sitting
Thread Starter
7th Gear
Joined: Jul 2014
Posts: 7
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From: Fishers IN
slight knock at start up after sitting
My 2007 Z51 LS2 has been knocking at start up after sitting for at least 24hrs. The knock goes away after a minute or so. Has anybody experienced this and if so what was the resolve?
Race Director
Joined: Oct 2010
Posts: 14,475
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From: Las Vegas NV
My 05 does it. It's more noticeable when it gets colder outside. It goes away as the oil heats up. I've heard it called piston slap. As far as I know its normal and there is nothing you can do about it.
Thread Starter
7th Gear
Joined: Jul 2014
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From: Fishers IN
I just thought it was abnormal because it's never done it before now. I just went over 20,000 miles and have never heard it until now. has your 05 done it all along or after a certain amount of miles?
Thread Starter
7th Gear
Joined: Jul 2014
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From: Fishers IN
Hi Truckplay..thanks for the info. I've got the LS2 6.0, have you heard of any issues with it? From what i've read about Piston Slap it's common in GM motors because of the way they are mass produced. Lawsuits galore on it.
Drifting
Joined: Jul 2007
Posts: 1,294
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Recent oil change?
Did you by chance change to a slightly thicker oil? 10w-40 perhaps? That may cause it to slap a bit because the thick oil can't get to the tight areas fast enough. 5W-30 only. :-). If you've used the thicker oil for a while, the slight accelerated wear from numerous cold starts might cause slight knocking.....forever. But in the end.....it's nothing to be concerned about. If the knocking goes away in a few seconds....you're good! (I'm a former aircraft mechanic....
"air-cooled" aircraft piston engines use very very thick oil (50w) with looser tolerances.....they all knock a bit before warming up). Aircraft engines are overhauled approx. every 2000 hours. That's the equivalent of approx. 120,000 miles on an automotive engine. If that indeed is your problem (normal or slightly accelerated engine wear). I wouldn't worry much if it goes away after several engine revolutions.
"air-cooled" aircraft piston engines use very very thick oil (50w) with looser tolerances.....they all knock a bit before warming up). Aircraft engines are overhauled approx. every 2000 hours. That's the equivalent of approx. 120,000 miles on an automotive engine. If that indeed is your problem (normal or slightly accelerated engine wear). I wouldn't worry much if it goes away after several engine revolutions.
Thread Starter
7th Gear
Joined: Jul 2014
Posts: 7
Likes: 0
From: Fishers IN
Did you by chance change to a slightly thicker oil? 10w-40 perhaps? That may cause it to slap a bit because the thick oil can't get to the tight areas fast enough. 5W-30 only. :-). If you've used the thicker oil for a while, the slight accelerated wear from numerous cold starts might cause slight knocking.....forever. But in the end.....it's nothing to be concerned about. If the knocking goes away in a few seconds....you're good! (I'm a former aircraft mechanic....
"air-cooled" aircraft piston engines use very very thick oil (50w) with looser tolerances.....they all knock a bit before warming up). Aircraft engines are overhauled approx. every 2000 hours. That's the equivalent of approx. 120,000 miles on an automotive engine. If that indeed is your problem (normal or slightly accelerated engine wear). I wouldn't worry much if it goes away after several engine revolutions.
"air-cooled" aircraft piston engines use very very thick oil (50w) with looser tolerances.....they all knock a bit before warming up). Aircraft engines are overhauled approx. every 2000 hours. That's the equivalent of approx. 120,000 miles on an automotive engine. If that indeed is your problem (normal or slightly accelerated engine wear). I wouldn't worry much if it goes away after several engine revolutions.
Thanks for the very insightful response. I would of guessed mechanic of some sort before you said it. This started about mid way through the oil change and now that I think about it, I can't verify the correct weight of oil that was used at it's last change. What you're saying makes sense, especially since it stops after a few seconds, indicating lube has arrived where needed. My first thought was something with the oil pump due to the nature of the knock. I'll do a quick oil change and see if it makes any difference, provided it's not permanent now..
Thanks again for your input!!!
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Racer
Joined: Jun 2012
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From: Hillsboro Oregon
I had a cold start knock with my LS3 that went away after 30 seconds or so. Only happened in the winter with cold oil temps. I figured it was a lifter. I have a bit of piston slap also, with cold oil, but it sounds different, lasts longer and only happens at around 2400 rpm with light throttle. Anyways, I think my lifter knock may have gone away `cause I've heard nothing all summer and recently my Vette sat for 2 weeks and upon starting, with 52 degree oil temp, no noise. So, my vote is for a noisy lifter.