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The trunk-type piston is a one piece design, with ring grooves machined in the piston dome area. Each piston is fitted with a fire ring, a compression ring, and an oil control ring. See Figure 25301 . ‪

1.Fire Ring ‪

3.Oil Control Ring ‪

2.Compression Ring ‪

4.Piston ‪

Piston Ring Location

Internal piston parts are lubricated and cooled by the engine oil. Oil is pressure-fed up the drilled passage in the connecting rod, through the piston pin, through the center hole in the bearing. A portion of oil lubricates the piston pin and bearing. The piston dome is cooled by a separate oil nozzle mounted in the block. ‪

Note: The matching of the piston and liner sizes is critical. See Figure 26765 .

Piston and Liner Grading

Repair or Replacement of Piston and Piston Ring

To determine if repair is possible or replacement is necessary, perform the following procedure. See Figure 25413 . ‪

Repair or Replacement of Piston and Piston Ring Flowchart

Removal of Piston and Piston Ring

refer to section for piston and connecting rod assembly removal procedure. ‪

Disassembly of Piston and Piston Ring

Disassemble the piston and piston rings as follows: ‪

  1. Using tool J 22405-02, remove the piston rings. See Figure 25302 .

    Piston Ring Removal and Installation


    The pin and piston must be match-marked to ensure proper reinstallation. ‪

  2. Using retaining ring pliers, remove two piston pin retainers.
  3. Remove the piston pin, and mark the front of the piston with a paint pencil. See Figure 25303 .

    1.Piston ‪

    3.Connecting Rod ‪

    2.Retainer Piston Pin ‪

    4.Piston Pin ‪

    Piston and Connecting Rod Disassembly

Clean the piston and piston rings prior to inspection as follows: ‪

  1. Clean the piston components with fuel oil.

    To avoid injury from flying debris when using compressed air, wear adequate eye protection (face shield or safety goggles) and do not exceed 40 psi (276 kPa) air pressure.

  2. Dry the piston with compressed air.
  3. If fuel oil does not remove carbon deposits, use a chemical solvent.
  4. Use a suitable tool or a piece of an old compression ring to clean the ring grooves.
  5. Clean the inner surface of the piston and the oil relief channels in the ring grooves.
Inspection of Piston and Piston Rings

Inspect the piston and piston rings as follows: ‪

  1. Inspect the piston as follows:
    1. Check for score marks, cracks, damaged ring grooves, or overheating indications.
    2. If any of these conditions are detected, replace the piston.
    3. Note: Burn spots may indicate an obstructed connecting rod or piston pin oil passage.

  2. Inspect the tapered compression ring groove. See Figure 26822 .

    Piston Ring Groove Dimensions

    1. Using the procedure listed above, inspect the compression ring groove.
    2. If the compression ring groove is worn beyond acceptable limits, replace the piston.
  3. Inspect the piston pin.
    1. Check the piston pin for fretting, cracking, or signs of overheating.
    2. If these are detected, replace the piston pin.
    3. Measure piston pin outside diameter. The diameter should be 52mm (0.008 in.).
    4. If the piston pin does not meet specifications, replace it.
    5. Note: If the piston pin is replaced for any reason, the piston pin bushing for that cylinder must also be replaced.

  4. Check the cylinder liner and block bore for excessive out-or-round, taper, or high spots. These could cause piston failure.

Piston Ring Gap of Piston and Piston Ring Assembly

Prior to piston ring installation, measure each piston ring gap. ‪

  1. Insert the piston rings into the cylinder liner one at a time. Use a piston to push the rings down.
  2. After the rings have been positioned, measure the ring gap of the top ring with a feeler gage. See Figure 25305 .

    Piston Ring Location

  3. Remove the ring from the liner after the measurement is complete.
  4. Repeat this procedure for each ring, and record your measurements. Allowable ring end gaps are listed in Table .

    Ring Description


    No. 1 Ring-Fire Ring ‪

    0.50-0.35 mm (.020-.014 in.) ‪

    No. 2 Ring-Compression ‪

    0.50-0.39 mm (.020-.015 in.) ‪

    No. 3 Ring-Oil Control ‪

    0.40-0.25 mm (.016-.010 in.) ‪

    Table Allowable Ring Gaps

Assemble the piston and piston rings as follows: ‪

Note: The oil control ring may be installed in either direction.

  1. Install the ring expander in the oil control ring groove. See Figure 25307 .

    1.Oil Control Ring ‪

    3.Piston ‪

    2.Oil Control Groove ‪

    4.Oil Control Expander Ring ‪

    Piston Ring Installation

  2. Install the oil control ring by hand.

    Note: Install expander into inside diameter groove of ring with expander spring gap located 1805 from the oil control ring gap.

    Install the fire and compression rings as follows: ‪


    To avoid breaking or overstressing the rings, do not spread them more than necessary to slip them over the piston dome. ‪

  1. Using tool J 22405-02, install the compression rings and fire ring.
  2. Stagger the ring gaps around the piston. See Figure 25308 .

    Piston Ring Installation and Positioning

  3. For piston and connecting rod assembly installation, refer to section .