3126B and 3126E Truck Engines Caterpillar

Two-Piece Articulated Piston

Illustration 1	g01139038

(1) Crown assembly

Top Ring and Intermediate Ring

(2) The top ring has the mark "UP-1".

Install the piston ring with the side marked "UP-1" toward the top of the piston. The colored stripe faces to the right of the ring end gap.

The ends of the piston ring have a clearance when the piston ring is installed in a cylinder with a specific bore size.

Cylinder bore size ... 110.025 mm (4.3317 inch)

Clearance ... 0.40 ± 0.10 mm (0.016 ± 0.004 inch)

The piston ring has an increase in clearance for each 0.03 mm (0.001 inch) increase in the cylinder liner bore.

Increase ... 0.09 mm (0.004 inch)

(3) The intermediate ring has the mark "UP-2".

Install the piston ring with the side marked "UP-2" toward the top of the piston. The colored stripe faces to the right of the piston ring end gap.

Thickness of the new piston ring ... 2.980 ± 0.013 mm (0.1173 ± 0.0005 inch)

The ends of the piston ring have a clearance when the piston ring is installed in a cylinder with a specific bore size.

Cylinder bore size ... 110.025 mm (4.3317 inch)

Clearance ... 0.825 ± 0.125 mm (0.0325 ± 0.0049 inch)

The intermediate piston ring has an increase in clearance for each 0.03 mm (.001 inch) increase in the cylinder liner bore.

Increase ... 0.09 mm (0.004 inch)

Oil Control Ring

(4) The oil control piston ring has a spring that is installed with the ring. The gap in the spring should be a distance of 180 degrees from the ring end gap when the oil control piston ring is assembled. The light green colored portion of the spring must be visible at the ring end gap.

Width of the groove in a new piston for the oil control piston ring ... 4.041 ± 0.013 mm (0.1591 ± 0.0005 inch)

Thickness of the new piston ring ... 3.985 ± 0.010 mm (0.1569 ± 0.0004 inch)

Clearance between the oil groove and the oil control piston ring ... 0.033 ± 0.079 mm (0.0013 ± 0.0031 inch)

The ends of the oil control piston ring have a clearance when the ring is installed in a cylinder with a specific bore size.

Cylinder bore size ... 110.025 mm (4.3317 inch)

Clearance ... 0.45 ± 0.15 mm (0.018 ± 0.006 inch)

The oil control piston ring has an increase in clearance for each 0.03 mm (0.001 inch) increase in the cylinder liner bore.

Increase ... 0.09 mm (0.004 inch)

After the piston rings have been installed, rotate the piston rings so that the end gaps are 120 degrees from each other.

(5) Piston skirt

Lubricate the entire piston in zone (A) prior to assembly into the cylinder block. Use clean engine oil.

Piston Pin Bore

(6) Piston pin

Piston pin bore diameter that is in the crown assembly ... 40.031 ± 0.007 mm (1.5760 ± 0.0003 inch)

Piston pin bore diameter that is in the piston skirt ... 40.020 ± 0.008 mm (1.5756 ± 0.0003 inch)

Piston pin diameter ... 39.993 ± 0.005 mm (1.5745 ± 0.0002 inch)

Length of piston pin ... 89.95 ± 0.15 mm (3.541 ± 0.006 inch)

Thoroughly lubricate the piston pin with clean engine oil prior to assembly.

(7) Connecting rod

Note: Install the rod and piston group in the engine with the part number to the rear of the engine. The rear of the engine is the flywheel end of the engine. Lubricate the rod and piston group with clean engine oil before you insert the rod and piston group into the block.