Tw!tchb!tch
02-21-2004, 10:00 PM
Copied from ls1.com . . . check it out .
Very interesting. I received a memo from GM explaining this after I took my 2001 Silverado for this problem. I purchased it before the SS. It has the 5.3L and it has piston slap, just like the SS. It has not affected performance at all, it now has 58000 miles. The memo read:
(GM MEMO START)
" COLD START ENGINE KNOCK
GEN III Engines 1998-present
It is characteristic to hear a knocking noise after starting a cold engine. Thiss noise will be present until the engine reaches full operating temperature. The lenght of this time and the degree of loudness will depend on: ambient temperature, engine temperature, interior selected and underhood sound deadening level of content.
Engineering has made changes to these engines that reduce rotating mass and internal friction. Specifically, this was done by a significant reduction in the lenght of the piston skirts, piston weight and wall thickness. These changes were done to improve fuel economy, meet customer performance expectations and adhere to government's environmental (EPA) and Cafe regulations.
Due to the thermal dynamics and the expansion rates of different metals and alloys, the pistons are shaped in a way that allows it to expand into a full circle. When cold the piston is not round. It is slightly oblong, its general shape is that of a figure eight "8". the lightweight materials used in the pistons expand at a different rate than the materials that make up the block and cylinder walls.
The factors result in internal clearances when the engine is cold that allow the piston to have a rocking motion in the cylinder, which is the cause of the sound(knock). When the engine reaches full operating temperature, these parts expand to their designed clearances and the knocking sound goes away. This typically will take 2-15 minutes depending on conditions. The clearances are designed to allow engines to operate in extreme temperatures from arctic to desert conditions and perform as required by their owners.
This noise is NOT a defect and does NOT affect the long term durability, function, or performance of the engine. "
(GM MEMO END)
Very interesting. I received a memo from GM explaining this after I took my 2001 Silverado for this problem. I purchased it before the SS. It has the 5.3L and it has piston slap, just like the SS. It has not affected performance at all, it now has 58000 miles. The memo read:
(GM MEMO START)
" COLD START ENGINE KNOCK
GEN III Engines 1998-present
It is characteristic to hear a knocking noise after starting a cold engine. Thiss noise will be present until the engine reaches full operating temperature. The lenght of this time and the degree of loudness will depend on: ambient temperature, engine temperature, interior selected and underhood sound deadening level of content.
Engineering has made changes to these engines that reduce rotating mass and internal friction. Specifically, this was done by a significant reduction in the lenght of the piston skirts, piston weight and wall thickness. These changes were done to improve fuel economy, meet customer performance expectations and adhere to government's environmental (EPA) and Cafe regulations.
Due to the thermal dynamics and the expansion rates of different metals and alloys, the pistons are shaped in a way that allows it to expand into a full circle. When cold the piston is not round. It is slightly oblong, its general shape is that of a figure eight "8". the lightweight materials used in the pistons expand at a different rate than the materials that make up the block and cylinder walls.
The factors result in internal clearances when the engine is cold that allow the piston to have a rocking motion in the cylinder, which is the cause of the sound(knock). When the engine reaches full operating temperature, these parts expand to their designed clearances and the knocking sound goes away. This typically will take 2-15 minutes depending on conditions. The clearances are designed to allow engines to operate in extreme temperatures from arctic to desert conditions and perform as required by their owners.
This noise is NOT a defect and does NOT affect the long term durability, function, or performance of the engine. "
(GM MEMO END)