N14 Base Engine Troubleshooting and Repair Manual – 001-043   Piston

All N14 Plus and N14 Industrial engines are equipped with articulated pistons.

The articulated piston is a two piece piston consisting of a forged steel crown and an aluminum skirt.

Remove the piston and connecting rod assemblies from the engine. Refer to Procedure

001-054-002.

NOTE: The piston and connecting rod assemblies

must
be installed in the same cylinder number from which they were removed to make sure there is a correct fit of worn mating surfaces if parts are used again.

Use a tag to mark the cylinder number from which each piston and rod assembly was removed.

Refer to Procedure

001-054-003 to disassemble the piston and connecting rod assembly.

NOTE: Refer to Procedure

001-047 for piston ring inspection.

CAUTION  To avoid damage to the piston crown, the cleaning solvent must be approved for bushing material.

Allow the pistons to soak for a minimum of 30 minutes in a tank containing an approved cleaning solvent for aluminum.

Use a hot, soapy solution and a non-metallic brush to remove carbon deposits.

NOTE: A plastic bead, Part No. 3822735, is available which can be used to clean pistons, including aluminum ring grooves. Do

not
bead blast pin bores.

CAUTION  Do not use a metal brush. A metal brush will damage the piston ring grooves. Do not use glass beads to clean the grooves. Walnut shell blasting can be used on grooves with a ni-resist insert and on the dome or crown of the piston. Use the minimum effective pressure and do not concentrate the spray in one area for an extended period of time. Do not use glass beads or walnut shell blasting on the aluminum grooves or pin bores. This can damage the pin bore surface finish or prevent the rings from seating correctly in the ring grooves.

Steam clean the pistons, and dry with compressed air.

Visually inspect both the crown and skirt. Do

not
use the crown or skirt if cracks or scuff marks are found. Scratches in the skirt are

not
acceptable if they are visually

not
acceptable.

Use crack detection kit, Part No. 3375432, or its equivalent to check for cracks on the piston crown and in and around the piston pin bore. Do

not
use if cracked or scuffed. If the crown is

not
acceptable, replace the crown and pin.

Visually inspect the piston ring lands and ring grooves for wear. A worn groove will have a detectable step at the back of the groove and a rolled edge at the surface of the piston or the ring groove outside diameter. Pistons exhibiting this wear are

not
acceptable for reuse.

Refer to the Parts Reuse Guidelines, Bulletin No.

3810303.

Measure the outside diameter of the piston as follows:

• Measure at right angles to the piston pin bore.
• Piston temperature

  must
  be between 21°C [70°F] to 32°C [90°F].

• Replace pistons that measure less than 139.50 mm [5.4922 inch] outside diameter.

Use piston ring groove wear gauges, Part Nos. 3823870 and 3823869, and a 5 to 6 inch micrometer to inspect the top and second grooves (compression rings).

NOTE: The piston

must
be replaced if measured dimensions are less than those in the table below.

Measure each ring groove (diameter over pins) when the piston temperature is at 21°C [70°F] in two places 90 degrees apart as shown.

Measure the piston pin bore when the piston temperature is at 20°C [68°F].

NOTE: Add 0.013 mm [0.0005-inch] to the bore inside diameter per 5°C [10°F] temperature rise up to 32°C [90°F].

Visually inspect the piston pin for scratches, grooves, or other damage. Do

not
reuse if it is visually

not
acceptable.

Measure the piston pin outside diameter at both ends as shown in two places 90 degrees apart.

NOTE: Discard the piston pin if it is more than 0.03 mm [0.001 In] out of round. If piston pin measurements exceed those in the table, do

not
reuse. If the piston pin is

not
acceptable for reuse, do

not
use the matching piston. Cummins recommends replacing pistons and pins in sets.

Inspect the connecting rod pin bushing bore and the crankshaft bore. Refer to Procedure

001-054-007.

To check the ring gap, install the new piston rings into the cylinder liner in which they will be used.

Use the top part of the piston to correctly position the ring in the liner.

Use a feeler gauge to inspect the ring gap. Replace the ring if it does

not
meet the following specifications:

NOTE: Add 0.08 mm [0.003-inch] to the maximum limit for each 0.03 mm [0.001-inch] wear in the cylinder liner wall.

Refer to Procedure

001-054-025 for poston and connecting rod assembly instructions.

Install the piston and connecting rod. Refer to Procedure

001-054-026.