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MBE 900 PISTONS, PISTON RINGS, AND CONNECTING RODS

The pistons are made of aluminum alloy with ring carriers and a shallow combustion chamber recess. The pistons are cooled by oil spray nozzles. The following illustration shows the piston and connecting rod assembly in an exploded view. See Figure 41980 . ‪

1. Piston and Rings ‪

5. Connecting Rod Cap ‪

2. Wrist Pin ‪

6. Connecting Rod Stretch Bolt ‪

3. Snap Ring ‪

7. Bearing Halves ‪

4. Connecting Rod ‪

Piston Assembly (exploded view)

Piston Removal

Remove the pistons as follows: ‪

  1. With the engine removed from the vehicle, remove the cylinder head and oil pan. Refer to section and refer to section .
  2. Using a plastic scraping tool, carefully scrape off any combustion residues from the combustion area in the cylinder in order to avoid damage to the piston rings when the piston is removed. See Figure 42299 .

    1. Plastic Scraping Tool ‪

    Cleaning the Cylinder Liner

    Note: Be sure the connecting rods and the bearing caps are marked so that they can be matched for installation. See Figure 42300 .

    1. Bearing Cap ‪

    2. Connecting Rod ‪

    Checking Rod and Bearing Cap Markings

    NOTICE:

    Do not damage the oil spray nozzles. It is helpful to remove them before proceeding. Damaged oil spray nozzles could result in a loss of oil pressure and cause engine damage. ‪

  3. Being careful not to damage the oil spray nozzles (see Figure 42301 ), remove the connecting rod stretch bolts and caps.

    1. Oil Spray Nozzle ‪

    Location of Oil Spray Nozzle

  4. Push the piston and connecting rod out of the cylinder, and remove it from the engine block.

    NOTICE:

    Be sure the vise jaws are adequately lined to prevent the rod surface from being nicked or marred in any way. Such surface damage could cause rod cracking or breaking. ‪

  5. Secure the connecting rod in a vise with protective jaws.
  6. Remove the wrist-pin snap rings. Push the wrist pin out and remove the piston from the connecting rod. At this time you may wish to remove and replace the piston rings. If so, refer to section .
Connecting Rod Inspection

The following commercially available tools are required for this procedure: ‪

  • Caliper, internal measurement, 40 to 60 mm
  • Caliper, internal measurement, 100 to 120 mm
  • Micrometer, 50 to 75 mm
  • Caliper gauge with dial indicator

Inspect the connecting rods as follows: ‪

  1. Inspect the connecting rod for blue discoloration (indicates bearing overheat damage), scoring, notches, and cracks. If any of these conditions are found, replace the connecting rod.
  2. Measure the inner diameter of the bushing in the small bore of the connecting rod. Use a caliper (internal measurement, 40 to 60 mm), dial indicator, and holder. See Figure 41995 .

    1. Dial Indicator ‪

    5. Bearing Shell (2 parts) ‪

    2. Holder, Dial Indicator ‪

    6. Bearing Cap ‪

    3. Bushing ‪

    7. Bolts (2 qty.) ‪

    4. Connecting Rod ‪

    Measuring Inner Diameters in the Connecting Rod

  3. If the value exceeds 40.04 mm (1.5764 in.), replace the connecting rod.

    Note: Checking the connecting rod for a twisted or bent condition in the next step requires machine shop equipment such as a caliper gauge with a dial indicator.

  4. Inspect the connecting rod for twisting and dimensional tolerance. See Figure 42303 . If any value exceeds those listed in Table , replace the connecting rod. Do not attempt to straighten the rod.

    Connecting Rod Measurements

    1. On each side of the connecting rod, measure the distance from the bearing bore (large bore) to the inner surface of the bushing. The measurement must be 157.445 to 157.510 mm (6.1986 to 6.2012 in).
    2. Measure the difference in axial parallelism between the bearing bore and the inner surface of the bushing, at 50 mm (2 in.) from the connecting-rod centerline. The maximum allowed difference is 0.025 mm (0.0010 in.).
    3. Description ‪

      Dimensions, ‪

      mm (in.) ‪

      Distance Between Connecting Rod Bearing Bore and Bushing Inner Surface ‪

      157.445157.510 (6.19866.2012 ) ‪

      Maximum Difference in Axial Parallelism Between Bearing Bore and Bushing Inner Surface ‪

      0.025 (0.0010) ‪

      Distance from Connecting Rod Center Line for Measuring Parallelism ‪

      50 (2) ‪

      Bushing Inner Diameter ‪

      40.0340.04 (1.57601.5764) ‪

      Bearing Seat Inner Diameter with Bearing Shells Installed ‪

      Standard ‪

      70.05470.093 (2.75802.7596 ) ‪

      Repair Stage: Undersize 0.1 mm ‪

      69.95469.993 (2.75412.7556 ) ‪

      Repair Stage: Undersize 0.25 mm ‪

      69.80469.843 (2.74822.7497) ‪

      Repair Stage: Undersize 0.5 mm ‪

      69.55469.593 (2.73832.7399) ‪

      Repair Stage: Undersize 0.75 mm ‪

      69.30469.343 (2.72852.7300) ‪

      Repair Stage: Undersize 1.0 mm ‪

      69.05469.093 (2.71872.7202) ‪

      Basic Bore Diameter for Connecting Rod Bearings ‪

      75.00075.019 (2.95282.9535) ‪

      Connecting-Rod Bearing Play ‪

      Radial ‪

      0.0390.098 (0.00150.0039) ‪

      Axial (end play) ‪

      0.1700.470 (0.00670.0185) ‪

      Permissible Out-of-Roundness of Basic Bores ‪

      Bearing Bore ‪

      0.008 (0.0003) ‪

      Bushing Bore ‪

      0.006 (0.0002) ‪

      Connecting Rod Bolt ‪

      Thread Diameter ‪

      M12 x 1.25 ‪

      Shank Length When New ‪

      56.0 (2.20) ‪

      Maximum Shank Length ‪

      57.0 (2.24) ‪

      Connecting Rod Inspection Specifications

Piston Installation

Install the pistons as follows: ‪

Note: If the engine block deck height has been reduced, you must install pistons with a reduced height.

  1. Position the connecting rod in the piston so that the far side of the rod contact surface (with the number on it) is on the right side (exhaust side) of the engine, and the arrow on the crown of the piston points toward the front of the engine.
  2. Install the wrist pin and secure it with the snap rings. See Figure 41984 .

    1. Piston ‪

    3. Far Side of Connecting Rod ‪

    2. Wrist Pin ‪

    Installing the Wrist Pin

  3. Coat the piston lightly with clean engine oil.
  4. Install new piston rings. Refer to section .
  5. Offset the ring gaps alternately by 120 degrees. See Figure 41985 .

    1. Piston ‪

    Ring Gaps Offset 120 Degrees

  6. Position a ring compressor loosely over the piston. Tighten the ring compressor on the piston so that it can just slide over the piston.
  7. Install the rod bearing half in the rod. Be sure that the bearing tang is fully seated in the groove of the rod. See Figure 41986 .

    1. Connecting Rod ‪

    3. Connecting Rod Cap ‪

    2. Bearing Halves ‪

    Installing the Rod Bearing Halves

  8. Coat the bearing surface lightly with clean engine oil.
  9. With the piston arrow pointing toward the front of the engine, push the piston into the cylinder until the rod bearing rests on the crankshaft journal. See Figure 42302 . Be careful not to scratch the crankshaft journals with the connecting rod.

    1. Piston ‪

    2 Ring Compressor ‪

    Installing a Piston

  10. Install the rod cap bearing half in the cap. Be sure that the bearing tang is fully seated in the groove of the cap. See Figure 41986 .
  11. Coat the bearing surface lightly with clean engine oil.
  12. Measure the connecting rod stretch bolts. Replace any bolts that exceed the maximum length of 57.0 mm (2.24 in.). See Figure 42304 . Lubricate the stretch bolt threads lightly.

    1. Shank ‪

    Measuring a Stretch Bolt

  13. Install the connecting rod cap on the connecting rod and hand-tighten the stretch bolts. Be sure that the marks on the cap and the rod match. See Figure 42300 .

    1. Bearing Cap ‪

    2. Connecting Rod ‪

    Checking Rod and Bearing Cap Markings

  14. Tighten the connecting rod stretch bolts alternately. Tighten each one in turn to the first stage and then go on to the next stage as listed in Table .

    Max. Shaft Length ‪

    Tightening Stage ‪

    Torque Value ‪

    Nm (lbft) ‪

    57.0 mm (2.24 in.) ‪

    Stage 1 ‪

    11 (8) ‪

    Stage 2 ‪

    45 (33) ‪

    Stage 3 ‪

    additional 90 degrees ‪

    Tightening Stages, Connecting Rod Stretch Bolts
  15. Rotate the crankshaft to make sure it turns freely.
  16. Using a dial gauge and holder, measure the piston projection relative to the top of the crankcase at all the pistons. See Figure 42305 .

    1. Piston ‪

    Piston Projection at Top Dead Center

  17. If the piston projection dimensions are not correct, replace the piston.
  18. Install the oil spray nozzles if they have been removed. Be sure they are seated and aligned correctly.
  19. Install the cylinder head and the oil pan. Refer to section and refer to section .

Piston Ring Removal

Remove piston rings as follows: ‪

  1. With the piston removed from the engine block, remove the rings, using suitable ring pliers. See Figure 41991 .

    1. Piston ‪

    2. Ring Pliers ‪

    Removing the Piston Rings

  2. Remove the rings in order, starting from the top of the piston down. See Figure 41990 .

    1. Keystone Piston Ring (Groove I) ‪

    3. Double Chamfered Oil Control Ring with Expander Spring (Groove III) ‪

    2. Taper Face Ring with Internal Angle (Groove II) ‪

    4. Piston ‪

    Piston Rings

Piston and Piston Ring Cleaning, Inspection, and Measuring

Clean, inspect, and measure the piston and piston rings as follows: ‪

  1. Clean all the carbon from the ring grooves.
  2. Be sure the grooves are not damaged, and that there are no burrs or combustion residue in the grooves.
  3. Before installing the new rings, check the end gap for the correct end gap measurements listed in Table .

    Note: Check the end gap of the upper two piston rings first. The must be removed from the third (lowest) piston ring before you can measure its end gap.

    Ring Designation ‪

    Groove ‪

    Gap When New ‪

    mm (in.) ‪

    Maximum End Gap ‪

    mm (in.) ‪

    Keystone ‪

    I ‪

    0.35 to 0.55 (0.014 to 0.022) ‪

    1.0 (.039) ‪

    Taper-Faced with Internal Angle ‪

    II ‪

    0.40 to 0.60 (0.016 to 0.024 ) ‪

    1.0 (.039) ‪

    Double-Chamfered Oil Control with Garter Spring ‪

    III ‪

    0.25 to 0.50 (0.010 to 0.020 ) ‪

    1.0 (.039) ‪

    Piston Ring End-Gap Dimensions
  4. Place each ring squarely into the combustion area of a cylinder liner or cylinder, then measure the end gap, using a feeler gauge. See Figure 41992 .

    Checking the Ring End-Gap

  5. Remove the spring expander from the third (lowest) ring, then measure its gap in the same way as the other two rings.

Piston Ring Installation

Install the piston rings as follows: ‪

  1. Install the spring expander into the ring. See Figure 41993 .

    1. Expander Spring ‪

    3. Expander Spring Joint ‪

    2. Piston Ring ‪

    Installing the Expander Spring

  2. Using ring pliers, install the rings. Make sure the word "TOP" on each ring is facing toward the crown of the piston. Install the rings in the reverse order of their removal; from the bottom to the top of the piston.
  3. Offset the ring gaps alternately by 120 degrees. See Figure 41994 .

    1. Piston ‪

    Piston Rings Offset 120 Degrees