Compatibility of Component Design Changes in Cummins ISX/QSX - Engine Builder Magazine
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Compatibility of Component Design Changes in Cummins ISX/QSX


Listed below are a few of the basic, although major, changes you may encounter when rebuilding an ISX/QSX engine:

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Head Gaskets: Early versions of these engines were produced with a multiple piece head gaskets to seal the cylinder head to the block. This design could only be used with the early “grooved top” liner design. Later versions were produced with an updated single piece head gasket and updated “flat top” liners. The new head gasket and liner design could be retro fitted back into the earlier engines, BUT only in full sets. The single piece head gasket must only be used with the later “flat top” liners.  


Cylinder Liners: As mentioned above, the early “grooved top” liners must be used with the multiple piece head gaskets The “flat top” liners must be used with single piece head gaskets. “Flat top” and “grooved top” liners cannot be mixed in an engine.

Pistons: Engines produced before 2003 were released with two piece articulated pistons. Many of these engines can be upgraded to one piece steel pistons (additional components may need to be changed to complete these conversions). Engines produced during and after 2003 were released with one piece steel pistons. One piece steel pistons must be used in complete sets and with drilled connecting rods. The skirt design of one piece pistons may also vary:


• Open skirt pistons have a large opening between the sides of the piston skirt and the crown. (Figure 1, left)

• Closed skirt pistons have a smaller opening between the sides of the piston skirt and the crown. (Figure 1, right)   

Care must be taken when replacing less than full sets of pistons within an engine since the actual piston design may have updated within an engine kit previously installed.


Connecting Rod Bearing: With the release of the one piece piston came updated drilled connecting rods and rod bearings. These later connecting rod bearings have a oil hole which allows the oil flow to continue up through the connecting rod to lubricate the piston pin connection. The drilled connecting rod bearing can be used in the older non-drilled rod, but a non-drilled bearing cannot be used with a drilled connecting rod or with a one piece piston. 


–Tech Tip courtesy of IPD

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