Cummins N14 STC, Celect, Celect Plus – Service 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 in Section 1.

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.

Use the following procedure to disassemble the piston and connecting rod assembly. Refer to Procedure 001-054 in Section 1.

NOTE: Use the following procedure for piston ring inspection. Refer to Procedure 001-047 in Section 1.

WARNING  When using solvents, acids, or alkaline materials for cleaning, follow the manufacturer’s recommendations for use. Wear goggles and protective clothing to reduce the possibility of personal injury.

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 Number 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.

WARNING  Wear appropriate eye and face protection when using compressed air. Flying debris and dirt can cause personal injury.

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 Number 3375432 or 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.

Reference the Parts Reuse Guidelines, Bulletin 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 in] outside diameter.

Use piston ring groove wear gauges, Part Numbers 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.

Ring Groove Wear Limits (Diameter Over Pins)

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

Piston Pin Bore (Crown Bore)

NOTE: Add 0.013 mm [0.0005 in] 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.

Piston Pin Outside Diameter

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 Inc, recommends replacing pistons and pins in sets.

Inspect the connecting rod pin bushing bore and the crankshaft bore.

Refer to Procedure 001-054 in Section 1.

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:

Piston Ring Gap

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

Use the following procedure for piston and connecting rod assembly instructions. Refer to Procedure 001-054 in Section 1.

Install the piston and connecting rod.

Refer to Procedure 001-054 in Section 1.