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SERIES 50 PISTON AND PISTON RING

The cross-head piston is a two-piece piston consisting of a dome and a skirt. The dome and skirt are held together by the piston pin. Ring grooves are machined in the piston dome. See Figure 24305 . ‪

1. Piston Pin ‪

5. Oil Ring Expander ‪

2. Piston Skirt ‪

6. Oil Control Ring ‪

3. Three-piece Bushing ‪

7. Compression Ring ‪

4. Piston Dome ‪

8. Fire Ring ‪

Piston and Related Parts

Note: Series 50G engine has a 3.5 mm fire ring, a rectangular cut compression ring and a 3-piece oil ring. See Figure 24307 and see Figure 35338 .The compression ring is identified with a purple stripe.

Piston Ring Packs

3piece Gas Oil Ring

To improve oil control, an improved 4.0 mm rectangular compression ring 23518373 was released to replace former keystone compression ring 8929845 in the second ring position. Due to this ring change the former piston dome 23516677 was replaced by current piston dome 23518374, part of current piston dome assembly 23518380. This change became effective on May 18, 1995, with production unit 4R9198. See Figure 27006 , see Figure 24307 and see Figure 35338 . ‪

1. Fire Ring ‪

6. Oil Control Ring ‪

2. Compression Ring ‪

7. Piston Dome ‪

3. Oil Control Ring ‪

8. Oil Ring Expander ‪

4. Fire Ring* ‪

9. Compression Ring* (Retangular) ‪

5. Compression Ring* ‪

10. Piston Dome (Retangular) ‪

* Note: Identification Mark to Face Top of Dome ‪

Piston Ring Location

As with the former ring, the current ring will be installed with the "football" mark facing up, see Figure 20198 . Due to the lower compression ratios from that of the diesel engines, there is no need to measure ring groove wear in the piston dome assembly of the 50G engine. ‪

Fire and Compression Ring Identification

All former parts and kits will be retained for service of diesel engines. Ring service kits are listed in Table . ‪

Service Kit

Former Part Number

Interim Part Number

Current Part Number

Piston Kit ‪

23516781 ‪

23518758 ‪

23519644 ‪

Cylinder Kit ‪

23516783 ‪

23518759 ‪

23519645 ‪

Ring Kit ‪

23505729 ‪

- ‪

23518760 ‪

Crankshaft Part Number History

A one-piece oil control ring is used in the third groove. The expander is of Spira-Lox construction. ‪

These channels are not drilled through the piston. The channels help the excess oil, scraped from the cylinder walls, return to the crankcase. See Figure 20190 . ‪

Piston Oil Relief Channels

The piston dome and piston pin bearing of the most recent design are separate parts and may be serviced separately. ‪

Two special bolts and spacers are used to attach the connecting rod to the piston pin. ‪

The solid-core piston pin has a drilled hole through the center to provide lubricating oil to the piston dome for cooling. A threaded hole on each side of the oil hole receives the connecting rod attaching bolts. See Figure 20191 . ‪

Piston Pin Cross Section

Internal parts of the piston are lubricated and cooled by the engine lubricating oil. Oil is pressure-fed up the drilled passage in the connecting rod, through the piston pin, then through the center hole in the bearing to the underside of the piston dome. A portion of the oil lubricates the piston pin and bearing. ‪

During engine operation, gas loads pushing down on the piston dome are taken directly by the piston pin and bearing. The piston skirt, being separate, is free from vertical load distortion. Thermal distortion is also reduced as the piston dome expands. As the connecting rod swings to one side on the downward travel of the piston, the major portion of the side thrust is taken by the piston skirt. ‪

Repair or Replacement of Piston and Piston Ring

To determine if repair is possible or replacement is necessary, perform the following procedure. See Figure 21778 . ‪

Flowchart for Repair or Replacement of Piston and Piston Rings

Cleaning and 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. Remove the piston rings with tool J 22405-02 . See Figure 20193 .

    Removing Piston Rings

    NOTICE:

    The pin, bushing, skirt and dome must be match-marked to assure proper position and orientation. ‪

  2. Withdraw the piston pin and mark or etch the front of the piston, so it can be returned to the correct cylinder location.
  3. Separate the piston skirt from the piston dome and mark or etch the front of the dome ear and skirt, so they can be returned to the correct location.
  4. Remove the piston pin bearings, marking the front of them, so they can be returned to the correct location.

Note: The lower pin bore bearings are removed from the pin bore first, by pushing the bearing legs outward by hand at the split lines from inside the dome saddle ear. The upper bearing may be held in the bore by oil on the back of the bearing, making removal from the pin bore by hand difficult.

EYE INJURY

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.

NOTICE:

Prying between the bearing back and dome bore may damage the dome saddle bore or raise burrs which will make installation of new bearings difficult. ‪

DDC recommends that compressed air be directed between the dome pin bore and back of the bearing at one end until the bearing pops up out of the bearing retaining hole. ‪

Inspection of Piston and Piston Ring

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

NOTICE:

Do not attempt to clean the piston skirt by glass beading. It will remove the tinplating. Do not refinish or polish the piston pin. ‪

  1. Clean the piston components with fuel oil.

    EYE INJURY

    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 components with compressed air.
  3. If fuel oil does not remove the carbon deposits, use a chemical solvent that will not harm the tinplate on the piston skirt.

    EYE INJURY

    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.

    NOTICE:

    After cleaning, do not leave glass beads in the piston dome. Do not allow the glass beading to contact any area of the piston pin bushing or pin bore. Glass beading will remove the tin plating. ‪

  4. The piston dome, including the compression ring grooves, is not tin plated and may be wire-brushed to remove any hard carbon. Glass beading can be used to clean a piston dome. Micro Bead Glass Shot MS-M (0.0029-0.0058 in.) is recommended. Allowable air pressure is 552-689 kPa (80-100 lb/in.2 ).

    Note: Do not wire-brush the piston skirt.

  5. Clean the ring grooves with a suitable tool or a piece of an old compression ring that has been ground to a bevel edge.
  6. Clean the inside surfaces of the piston dome and skirt and the oil relief channels in the oil ring grooves.

Inspect the piston and piston rings as follows: ‪

  1. Inspect the piston skirt and dome.
    1. Check the skirt and dome for score marks, cracks, damaged ring grooves or overheating indications.
    2. If any of these indications are present, the piston must be replaced.
    3. Note: Burn spots may indicate an obstruction in the connecting rod or piston pin oil passage.

  2. Inspect the tapered fire ring groove (top) in the piston dome.
    1. Using the piston ring land step gage, J 35884-A or J 38609-A , check tapered fire ring groove. See Figure 20194 .
    2. Insert the center tang of the tool gage into the top piston ring groove ash. See Figure 20194 .
    3. Hold the tool at a 90 angle to the ring groove to prevent false readings.
    4. With the center tang into the ring groove as far as it will go, there should be no contact of the piston with the shoulder of the gage. If the gage makes contact at point A or point B, the fire ring groove is worn beyond usable limits. Check the groove clearance at 4 spots, at 90 intervals. Measure the ring land parallel to and at 90 to the wrist pin.
    5. If fire ring groove is worn beyond usable limits, replace piston dome.
    6. 1. Fire Ring Groove ‪

      Checking Fire Ring Groove

  3. Inspect tapered compression ring groove (second) in the piston dome.
    1. Using piston ring land step gage, J 38689-A , check the groove.
    2. If the compression ring groove is worn beyond usable limits, replace piston dome.
  4. Inspect the piston pin.

    NOTICE:

    If piston pin is replaced for any reason, the piston pin bushing for that cylinder must also be replaced. ‪

    1. Check the piston pin for fretting, cracking or signs of overheating.
    2. If these are detected, replace piston pin.
    3. Measure piston pin outside diameter. Specifications are listed in Table .
    4. If piston pin is out of specs, replace with new part.
  5. Inspect the piston pin bushings.

    NOTICE:

    If a piston pin bushing is replaced for any reason, the piston pin for that cylinder must also be replaced. ‪

    1. Check the piston pin bushings for scoring, pitting, flaking, cracking, excessive wear, or signs of overheating.
    2. If these conditions are present, the bearings must be replaced.
  6. Inspect the back of the upper bushing.
    1. Check the bushing for excessive fretting.
    2. If excessive fretting is evident, replace all three bushings.
    3. The corresponding fretting in the piston dome can be removed using crocus cloth, wet with fuel oil.
  7. Inspect the edges of the bearings and piston dome pin bore.
    1. Check the edges of the bearing and piston dome pin bore for dents and dings.
    2. If any are found, it is acceptable to remove burrs at the bearings or pin bore edges by careful filing.
    3. Note: Remove any dirt or debris on the backs of the bearing or dome pin bore that may take up clearance required for bearing or piston pin installation.

  8. Check the cylinder liner and block bore for excessive out-of-round, taper or high spots which could cause failure of the piston. Specifications are listed in Table .
  9. Check the block bore for excessive out-of-round, taper, and high spots which could cause failure of the piston. Specifications are listed in Table .

Assembly of Piston and Piston Rings

Prior to installing the piston rings, the ring gap of each piston ring must be measured. ‪

  1. Insert the piston rings inside of the cylinder liner one at a time, using a piston dome (inserted upside down into the liner) to push the ring down. The piston dome should be inserted into the liner, to the same depth as the ring being positioned.
  2. For the oil control ring, insert the piston dome down into the liner, until the oil control ring land is just into the liner. This will ensure that the rings are parallel with the top of the liner, and that they are positioned in the liner within the normal area of ring travel.
  3. After the three rings have been positioned in the liner, measure the ring gap of the top ring with a feeler gage. See Figure 20199 . 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 .

    Piston Ring Location

    Ring

    Ring End Gap

    Fire Ring (2.5 mm [0.098 in.] chrome) ‪

    0.40-0.87 mm (0.016-0.034 in.) ‪

    Fire Ring (3.5 mm [0.138 in.] plasma) ‪

    0.51-0.87 mm (0.020-0.034 in.) ‪

    Compression Ring ‪

    0.81-1.31 mm (0.032-0.051 in.) ‪

    Oil Control Ring ‪

    0.40-0.81 mm (0.016-0.032 in.) ‪

    Allowable Ring End Gap
  5. Refer to Section for assembly of rings for diesel engines or refer to Section for S50G engines.

Assembly of S50 Diesel Piston Rings

Assemble the S50 diesel engine piston and piston rings as follows: ‪

  1. Install the ring expander in the oil control ring groove in the piston. See Figure 20200 .

    Note: Install expander into inside diameter groove of ring with expander spring gap located 180 from the oil control ring gap.

    1. Oil Control Ring ‪

    3. Piston ‪

    2. Oil Control Ring Groove ‪

    4. Oil Control Ring Expander ‪

    Piston Ring Installation

  2. Install the oil control ring by hand. See Figure 20201 .

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

    Oil Control Ring Installation

The oil control ring expander has a white paint stripe. Make sure the paint mark can be seen after the oil control ring is installed at ring gap. ‪

Install the S50 diesel engine fire and compression rings as follows: ‪

NOTICE:

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

  1. Starting with the compression ring (second groove), install the compression ring and fire ring with tool J 22405-02 . See Figure 20202 . Make sure the identifying dimple on the rings is installed up, toward the dome of the piston. See Figure 20198 for ring identification and locations.
  2. Stagger the ring gaps around the piston. See Figure 20202 .

    Piston Ring Positioning

  3. Refer to Section for piston and connecting rod assembly procedure.

Assembly of S50G Piston Rings

Install the oil control ring for the S50G engine as follows: ‪

  1. Install the expander in the bottom groove of the piston.
  2. Install the upper and lower rails ensuring one is on the upper side of the expander and the other is on the lower side of the expander.

    Note: The expander and both rails may be installed with either side up. There is no "football" mark on any of the three oil ring components for natural gas engines.

  3. Orient the ring gaps of the rails 180 degrees apart so that they align with the paint marks on the expander. The expander should be 90 degrees from the oil ring gaps.

Install the compression and fire ring for the S50G engine as follows: ‪

  1. Install the compression ring (rectangular cut shape) in the second groove of the piston, using tool J 22405-02 .
  2. Install the fire ring in the top groove of the piston, using tool J 22405-02 .
  3. Stagger the ring gaps around the piston. See Figure 35362 .

    Top View of Piston Dome

  4. Refer to Section for piston and connecting rod assembly procedure.