Power assembly

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In Electro-Motive Diesel (EMD) parlance, a "Power assembly" is a complete unit, consisting of all major components in a cylinder, including:

  • Cylinder head (including the four exhaust valves but not the Unit injector or Electronic unit injector)
  • Cylinder liner (including the integral water-cooling jacket and scavenging air intake ports)
  • Piston
  • Piston carrier (and thrust washer)
  • Piston rod (either "fork" or "blade")

Using a special fixture and ordinary shop tools, an EMD power assembly may be changed within a few hours, requiring no other major engine subsystem disassembly.

The design is central to EMD's maintenance concept, and whether one or all 8, 12, 16 or 20 power assemblies are to be changed, the procedure is the same.

The components within a power assembly may be inspected and may be evaluated without disassembly of any other major components. The use of a fiber optic endoscope (flexible borescope) may facilitate this inspection and evaluation, but this is not a requirement, nor is it a part of EMD's maintenance procedures. All power assembly above-piston structures, including the piston top, may be inspected and evaluated through the scavenging air ports when the piston is at bottom dead center (through the cylinder's "Air Box hand-hole"). Also, the sides of a piston, and each piston ring, may be inspected and evaluated at positions intermediate between top dead center and bottom dead center. And, similarly, all below-piston structures including the piston carrier, piston rod and other components may be inspected and evaluated (through the cylinder's "Crank Case hand-hole").

Indeed, all cylinders may be inspected and evaluated in one revolution of the crankshaft. In this case, the engine is "barred over" (rotated manually using a bar) between each cylinder position (the engine is never "inched" using the starter motors).

A power assembly's Unit injector (UI) or Electronic unit injector (EUI) may be replaced or reused, as indicated by the inspection/evaluation.


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