Piston slap?
:sad:
12-08-2008, 10:55 PM
#12
Short-skirt pistons. There just isn't much to prevent them from rocking. The stubby lightweight pistons is one of the reasons Gen-III/IV engines can rev past 6k without exploding, it's also why the ring lands are so narrow they break with even slight detonation.
12-09-2008, 01:26 AM
#15
This noise has been a customer concern since 1997, when the LS1 was introduced in the Corvette. Then again in every vehicle it has been introduced in, including our trucks. My truck has made this noise for as long as I can remember. In fact, GM came out with a way for us to handle this at the dealerships. If a customer complained about the noise, we gave them information about the noise, and the GM customer service phone number. They could then call GM and recieve a "component letter". This letter gave them a 10 year/100,000 mile warranty on the engine, and its internal components. Its intention was to give the customer peace-of-mind. I can tell you that no engine has ever failed from this condition. I can also tell you(by talking to employees at other brands dealerships) that this condition exists with Dodge, Ford, Subaru, Toyota, and Nissan.
Talk to any engine machinist who has been "on the job" for a long time, and when they are going to bore your engine, they will bore it differently for forged pistons vs. cast pistons. Cast pistons stay the same size(for the most part) with cold to hot engine temps. Forged pistons shrink when they are cold, expand when at operating temp. A good machinist will always bore a little extra if you are using forged pistons. Add to that, these engines are not just forged pistons, they also use skirtless forged pistons. No skirts on the pistons to keep them centered in the bore. While they are cold, they flop around some, and make noise. This is not a bad thing, they can handle the stress, if you don't abuse them while cold. GM used these(along with most other manufacturers) because they are a low friction design that is strong. That adds power(low friction) and longevity and strength(forged).
Your noise is normal, and you should not worry.
Talk to any engine machinist who has been "on the job" for a long time, and when they are going to bore your engine, they will bore it differently for forged pistons vs. cast pistons. Cast pistons stay the same size(for the most part) with cold to hot engine temps. Forged pistons shrink when they are cold, expand when at operating temp. A good machinist will always bore a little extra if you are using forged pistons. Add to that, these engines are not just forged pistons, they also use skirtless forged pistons. No skirts on the pistons to keep them centered in the bore. While they are cold, they flop around some, and make noise. This is not a bad thing, they can handle the stress, if you don't abuse them while cold. GM used these(along with most other manufacturers) because they are a low friction design that is strong. That adds power(low friction) and longevity and strength(forged).
Your noise is normal, and you should not worry.
12-09-2008, 06:30 AM
#17
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i would sea foam it...my truck used to slap like no tomorrow...it was awful...usually would do it after 1500-2000 miles after my oil change...i sea foamed in last spring and its around 10* outside and its starts up and doesnt make a noise(knock on wood)lol...the only other thing i changed was running Pennzoil to Cen-pe-co oil and i think that helped a lot!
My last truck, an 03 had 36K in 2 years from commuting, I moved closer to work when I bought this truck. Sometimes the drive is too short 
