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Old 06-26-2009, 01:35 PM   #2

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Drives: 2019 Louis Chevrolet Camaro
Join Date: Mar 2008
Location: SW Florida
Posts: 4,199
It's called piston slap.

Common in many GM engines.

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 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.

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