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Discussion Starter #1
My 09 ZO6 has 26K on it. About a month ago, it started making a distinct rat-tat-tat sound from the engine on initial start up in the morning. The noise would continue around 1400-1600 rpms primarily but heard up higher also. If I parked the car, shut it off and came back 1/2 hour later, the noise was barely audible if at all.
I've read the threads on valve train noise over and over. I took the car to the dealer where the guides were checked and apparently, no problem there. There was a bulletin regarding engine noise related to oil aspiration where the O ring in the dry sump tank would go bad, therefore causing the pipe in the tank to rattle. That was just replaced last Friday and the noise was very audible a day later. If the car sits overnight, the very next start up is very audible.
Might be on the wrong track but it sounds like a piston slap or knock, the warmer it got the more it went away.

Any thoughts, suggestion, or ideas that anyone has encountered regarding this issue? Please help:)
 

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You need to hook up with a OBD scanner and record while doing this startup and idle

Then check that for what oil pressure scanner reports, any error codes, misfire or knock counts would point if in fact a internal engine issue or not.

I would assume everyone has engine checked for proper oil level ( cold and hot) and type used ?
 

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Discussion Starter #4
FOR ALL CONCERNED:
Well, after a few days at the dealership, my tech buddy finally heard the rat-tat-tat sound when he started it up cold. At least now he definitely knows I wasn't hearing things! As he went into it the engine, he narrowed down to cylinder #3, pulled rocker arms and push rods for that cylinder, started the engine and the noise was gone. At this point, he's leaning toward the cam and/or lifters that went south. He's going pull the head to make sure there's no cylinder wall or piston damage to the bottom end. He's only done one other LS7 for a wiped lob on a cam and that too was cylinder #3. :usa:
 

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Discussion Starter #6
As of Monday, 2/4/13, tech pulled head and discovered valve guides were extremely worn especially on exhaust valves. He's confident that when he pulls the passenger head, he'll find the same results. This is a stock engine with 26000 miles.
GM has authorized him to replace both heads. As of Wed, 2/6, heads were on back order, don't have a definitive date yet when they become available. Will post when car is back on the road :mah:
 

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Your year and issue has a TSB from GM, and if experiencing the sound it's the heads. GM found the issue upon warranty work and discovered it was a machining error of the supplier. The other forum has a bit of info on it. GM doesn't want a run of people reading on the internet and then coming in complaining so it's not a recall. They also have tried to charge people who want their heads checked?? But if it falls into the sound they warranty the heads. So many Z's have low mileage so I am sure they are hedging their bets that most have this problem out of warranty. Otherwise they would have recalled the years in question. This really makes me want to buy another corvette when this is how they stand behind it.... They know it's an issue, and you have to know about it to get it covered.
 

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Discussion Starter #10 (Edited)
nfran2,

Thank you for the update!

Evan, Chevrolet Customer Service
Evan, perhaps you can shed some light on this problem. It seems that the LS7 heads from GMPP #12578449 or the stock LS7 heads are on back order. My tech, along with the parts manager of the dealership have been trying to get a simple answer has to how long I have to wait to get a pair of brand new heads for my ZO6. They've tried for 4 straight days with not resolution yet. Very frustrating for them as well as me:(
Any help or insight you can offer would be greatly appreciated. :mah:
 

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nfran2,

Could you private message me your information (name, number, address, VIN, current mileage, and involved dealership)?

Evan, Chevrolet Customer Service
 
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