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

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:


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

You May Also Like

Going the Extra Mile with Cylinder Head Porting

It’s not just the port work alone that creates spectacular cylinder head performance. The most critical areas of a cylinder head are those which pass the most air at the highest speed and for the longest duration. Your bowl area, the valve job, the throat diameter, and combustion chamber are all crucial parts. 

Every engine builder is after the ultimate in performance gains. When it comes to cylinder head performance, we’re all trying to maximize airflow to create more power. In order to accomplish that, builders have to know what to manipulate in order to make improvements. Those improvements to airflow quality and quantity come from porting and removing areas of restriction.

Tight Tolerances and Building Power

As you ascend Mt. Everest, you reach an area called the death zone. Once you climb high enough, the margin of error becomes perilously thin. That death zone also applies to engines. As the horsepower per cubic inch and rpm increase, the margin of error decreases. 

CNC Update: Features and Automation

Precision is key when it comes to automotive parts; the complex designs of connecting rods, pistons and rings, blocks, cylinder heads, and other parts require super tight tolerances that are getting more and more difficult to be met by hand or with other machining processes outside of CNC.

All Things Media Blasting

Engine building is a segment of the automotive industry that has always been ahead of the curve in media blasting, and no matter the engine shop, cleaning equipment is a common bond.

Engine & Hub Dynos: Necessary Tools and Additional Revenue

Being able to see the horsepower and the direct correlation to what is lost in the driveline is invaluable – dynos offer a myriad of benefits for the modern engine shop.

Other Posts

November 2022 Shop Solutions

November tricks and tips for the shop!

Shop Solutions October 2022

When machining on the CNC mill, it’s necessary to blow the flood coolant and chips off the parts for inspection. I tried a tool holder mounted fan, but it wouldn’t get all the chips and coolant out of the deeper areas.

Could Engine Oil Soon Contain No Oil?

The trend towards ever thinner engine oils is an effort to reduce fuel consumption and emissions. How far can it go?

Building Big Block Marine Engines

Find out what it takes to build a formidable marine engine.

Marine Engines