Around 1998, GM switched from a "Select Build" method of manufacturing and/or assembling engines to a "Net Build" method, in order to save money on manufacturing and/or assembly. In the Select Build process, pistons and cylinders are matched for size and fit. GM's new "Net Build" method of manufacturing and/or assembly, in contrast, assumes all pistons will fit equally well in all cylinders and does not allow for variations in the size of engine cylinders or pistons. The pistons of slightly varying size (all within spec) are not individually matched with the cylinders of slightly varying size (all within spec).

Excessive “piston slap” occurs because an automobile manufacturer (GM) designs and/or manufactures a defective engine in which the clearance between the piston and cylinder bore is too great. Essentially, the piston moves sideways and “slaps” or “knocks” hard against the cylinder bore and causes damage to the engine pistons and cylinders, excessive smoke emissions, excessive oil consumption, carbon buildup on piston heads, decreased mileage, and a loud and obnoxious “slapping” or “knocking” noise, all of which diminishes vehicle resale value in the trade.

"...a knocking engine could lower the value of a vehicle by $4,000 to $6,000 at trade-in"
Charlie Vogelheim, executive editor for Kelley Blue Book
Detroit Free Press

"The very evidence provided by the manufacturer (GM) to indicate this condition is not a problem ultimately demonstrates that it is a problem."  
California BBB Arbitrator

2007's and 2008's with piston slap?

GM Consumers, do you have a 1999-???? 3.1, 3.4, 4.3, 4.6 (Northstar), 4.8, 5.3, 5.7(LS1), 6.0 or 8.1 liter engine that displays any of the following problems?

	A loud embarrassing and annoying internal engine knock.  Many are defective due to design and manufacturing quality consistency problems.  Listen to piston slap here.
	Higher than normal levels of wear related materials in oil analysis samples performed by independent laboratories.
	Vertical piston and cylinder wall scuffing/scratching or scoring on the hammering (noisy) cylinders upon visual inspection.  See photos here.
	Reduced combustion chamber compression on the hammering (noisy) cylinders.
	Increased oil consumption.
	Increased exhaust emissions.
	Did GM or there agents tell you they would fix your defective vehicle in writing/and/or verbally when the phantom "New Piston" fix WAS TO arrive in the spring or summer of 2002?  GM did in fact admit it had a problem and that its engineering department was working on the fix. The fix was promised to be made to consumer’s engines in the spring or summer of 2002. As the number of slapping engines grew and the cost to repair them grew as well, GM changed its policy.