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Old 05-07-2011, 07:13 AM   #31
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I dont recall the slap issue being caused by the aluminum blocks. It was due to the expansion rate of the pistons themselves, because most of the vehicles that had slap were the iron block trucks (which is probably because way more trucks had those engines than cars did at the time).
Piston slap is caused when there's too much space between the piston and the cylinder wall. The piston moves up and down in the cylinder and the extra clearance results in a greater amount of rocking in the cylinder, producing a loud knocking noise. Vehicles with the engine knock problem include 1999 - 2002 GMC and Chevy pickups and sports-utility models with 3.1, 3.4, 4.3, 4.6 (Northstar), 4.8, 5.3, 5.7(LS1), 6.0 or 8.1 liter engines. Specific models include (but may not be limited to): Chevrolet Silverado, Tahoe and Suburban, GMC Sierra, Yukon and Yukon XL. The 2002 Cadillac Escalade SUV also reportedly suffers from the problem.
GM spokeswoman Deborah Frakes states: "the only known effect of this condition is an audible sound that typically occurs during the first five to thirty seconds after starting" and that "the condition does not create any degradation of durability, performance or safety." In fact, in several of their Technical Service Bulletins (TSB's), GM claims that the "Cold Start Knock" is normal.
Consumers have differing opinions. GM truck owners complain that piston slap damages the engine and causes excessive oil and fuel consumption. Many consumers suffering from piston slap report that the knocking is constant, lasting well beyond the initial start-up, and appears regardless of the temperature. Additionally, consumers argue that the problem lowers the value of their vehicle when they try to sell it or trade it in
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Old 05-07-2011, 08:39 AM   #32
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Piston slap is caused when there's too much space between the piston and the cylinder wall. The piston moves up and down in the cylinder and the extra clearance results in a greater amount of rocking in the cylinder, producing a loud knocking noise. Vehicles with the engine knock problem include 1999 - 2002 GMC and Chevy pickups and sports-utility models with 3.1, 3.4, 4.3, 4.6 (Northstar), 4.8, 5.3, 5.7(LS1), 6.0 or 8.1 liter engines. Specific models include (but may not be limited to): Chevrolet Silverado, Tahoe and Suburban, GMC Sierra, Yukon and Yukon XL. The 2002 Cadillac Escalade SUV also reportedly suffers from the problem.
GM spokeswoman Deborah Frakes states: "the only known effect of this condition is an audible sound that typically occurs during the first five to thirty seconds after starting" and that "the condition does not create any degradation of durability, performance or safety." In fact, in several of their Technical Service Bulletins (TSB's), GM claims that the "Cold Start Knock" is normal.
Consumers have differing opinions. GM truck owners complain that piston slap damages the engine and causes excessive oil and fuel consumption. Many consumers suffering from piston slap report that the knocking is constant, lasting well beyond the initial start-up, and appears regardless of the temperature. Additionally, consumers argue that the problem lowers the value of their vehicle when they try to sell it or trade it in
Yes I know what piston slap is, and you made my point for me. Most of those tsb's refer to GM trucks with iron blocks, which points at the pistons themselves as the culprit, not the aluminum block (which use iron liners anyways). The GM fix came in 2003 (the main reason I purchased my first Silverado that year and not before btw) when GM used a revised ring pack with a Napier style ring which all but cured the problem. I guess the new 6.2s don't use the more expensive rings tho, not sure. My 4.8 never makes noise, knock on wood
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Old 05-07-2011, 01:15 PM   #33
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So, how could you distinguish between piston slap, wrist pin and lifter noise.

My 6.2 is really noisey, like a diesel, on cold start but there is still audilbe noise at full
temp, but you have to listen for the noise once it is warm.

I have pulled the plug wires one at a time and there was no change in the sound.

this is my 5 th LS engine truck and the only one that has made this noise, the 2000 5.3 had a bit of cold start noise , but no where near what this one does, the others were all quiet.

The dealer has already told me it piston noise but I am not so sure.
They told me to do a combustion chamber cleaning, which I have done and no change in the sound.

Any way to fiqure out the source of the noise?
i dont know much about the 6.2s but i beleive they are direct injected wich is a noisy set up. that could be what your hearing.
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Old 05-07-2011, 01:55 PM   #34
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i dont know much about the 6.2s but i beleive they are direct injected wich is a noisy set up. that could be what your hearing.
thanx for the reply but that is a negative. Same basic engine.

Truck now has 20km, about 12,000 miles.
It sounds like a diesel.
Started making noise in Feb.
I am not happy.
Been a GM dude for a long time, this sucks on a 40k truck.

If it is was lifters, ok, fixable, wrist pin, fixable.
Piston slap, they won't fix it.
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Old 05-07-2011, 08:45 PM   #35
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Quote:
Originally Posted by Allgonoshow View Post
So, how could you distinguish between piston slap, wrist pin and lifter noise.

My 6.2 is really noisey, like a diesel, on cold start but there is still audilbe noise at full
temp, but you have to listen for the noise once it is warm.

I have pulled the plug wires one at a time and there was no change in the sound.

this is my 5 th LS engine truck and the only one that has made this noise, the 2000 5.3 had a bit of cold start noise , but no where near what this one does, the others were all quiet.

The dealer has already told me it piston noise but I am not so sure.
They told me to do a combustion chamber cleaning, which I have done and no change in the sound.

Any way to fiqure out the source of the noise?
If it's a lifter the noise will be at half the speed of the crankshaft, and I believe that a wrist pin noise will go away or change when combustion is removed, but I'm not 100% sure (I know for sure that a rod knock will, but really haven't dealt with too many wrist pin problems). Piston slap will remain the same when you remove spark or fuel, and my guess is that this is your issue.
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Old 05-08-2011, 12:22 PM   #36
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Originally Posted by budhayes3 View Post
If it's a lifter the noise will be at half the speed of the crankshaft, and I believe that a wrist pin noise will go away or change when combustion is removed, but I'm not 100% sure (I know for sure that a rod knock will, but really haven't dealt with too many wrist pin problems). Piston slap will remain the same when you remove spark or fuel, and my guess is that this is your issue.
Unfortunately you are probably correct, I was hoping it would a lifter or something fixable.
it's not looking that way.
Thanx for the input.
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Old 05-08-2011, 12:22 PM
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