RACK 6W5546 - Caterpillar

G3406 (4FD) Engines, G3408 (6NB) Engines, G3412 (7DB) EnginesGallery cooled pistons are now used in the G3400 Family of Engines. A stream of oil is directed at the wrist pin and at the entrance to the piston gallery from a jet located in the bottom of the cylinder block. The oil circulates around the interior of the piston through a gallery cast in the piston body. The gallery cooled piston improves piston cooling, increases the detonation margin, and provides less oil consumption and better oil life.
All G3406 (4FD) Engine arrangements receive the gallery cooled pistons. All G3408 (6NB) and G3412 (7DB) Engine arrangements receive the gallery cooled pistons except the low speed, low compression ratio arrangements (8.5:1 CR, 1000-1400 RPM). The following chart shows the effective serial numbers for engines with gallery cooled pistons.
If gallery cooled pistons are installed, it is recommended that all cylinders on an engine be fitted with them. The pistons should not be installed without the new oil spray jets. The new spray jets are installed in the same location as the old spray jet with the same bolt. The new oil jets provide the additional cooling necessary for the tighter tolerances between the piston and cylinder wall. The parts per cylinder needed to install the gallery cooled piston are shown in the following chart.