Piston slap?
12-09-2008, 10:18 AM
#21
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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.
Even the supercharged 556hp 2009 Cadillac LSA engine uses cast pistons. As does the 505hp LS7.
Again theya re NOT forged, they are a cast hypereutectic cast aluminum desgn. Hypereutectic simply means "High Silicon". The main reason a high silicon cast piston is used is the HYPER piston actually expands less than a HYPeutectic(low silicon) cast piston. This allows teh OEMs to use tigher poiston to wall clearances in an order to lower pollution levels(blowby, raw fuel caught in piston rings when cold).
These high silicon pistons are more brittle however and they will crack easier during pre igition/detonation.
The hyper pistons used in forced induction appliocations usually have a lower percentage of silicon than NA applications, thus making them less brittle.
But you are correct about boring a cast piston engine and forged piston engine differently, the forged piston needs the extra room to grow, thus looser piston-wall clearances are used.
peace
Hog
Last edited by hog; 12-09-2008 at 10:27 AM.
12-09-2008, 10:45 AM
#22
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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.
HAHA, hog beat me to it, I type to slow.
12-09-2008, 04:41 PM
#23
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When i first put the 6.0 in there was no noise, but a few months later i have a sort-of loud piston lap, especially the colder the engine is. I took it by Texas speed and had them check it out and they said that that was normal, and it was probably just piston slap.
12-09-2008, 05:51 PM
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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!
i tried sea foam. didn't make a difference. i probably should of sucked it up through the vaccuum hose. is that what you did JakeBrake? i put mine directly in the crankcase.
i have lucas oil treatment in my truck right now. that doesn't make a difference either. the temp outside plays a huge role in its severity .
12-09-2008, 06:44 PM
#29
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in other words my brother in laws 06 truck just started makin noise a few months ago out of no where. he called me and told me he was taking it to the dealership, i told him not to waste his time that they all do it in time. thats how i got the 6.0 block i have now, it started the piston slap, person didnt like it and wanted a new motor, i got the old one. as long as it has all the signs of normal piston slap i wouldnt worry too much about it.
12-09-2008, 07:06 PM
#30
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I have no answers but a question about sea foam. What do your cats and o2s think about getting all the carbon crap blown out through them/stuck in the cat? Are you supposed to remove anything before you do it?