The Cummins ISX was originally called the “signature” series, and was developed to replace older N14 engines. These Cummins ISX/QSX engines have been subject to numerous updates and design modifications, which is no surprise given their wide power range of 430-650hp. The ISX has become a very popular power source, and is used in on-highway and vocation trucks, while the QSX is used in a variety of industrial, agriculture, marine, and off-highway applications. The earlier version of this engine was a dual overhead camshaft design, while the latter ISX15/QSX15 version has a single camshaft and includes an XPI (eXtreme high Pressure Injection) common rail fuel system.
In previous publications, we’ve addressed some of the changes, updates, and precautions regarding the Cummins ISX/ QSX 14.9 and 15 liter engines. Some of the updates are of no concern if you are doing an overhaul, however, for those repairing an engine by replacing only select components, it can be a challenge since the replacement parts may not be compatible with the remaining components in the engine. This is especially relevant if cylinder components are involved. The intent of this article is to explain the design changes in the ISX/ QSX cylinder components, and the recent introduction of an APR (anti-polishing ring pistons and liners).
There are three types of connecting rods to be aware of, and each has an associated rod bearing. The early engines had non drilled rods, later engines had drilled rods that are “saw cut” or machined on the surfaces between the rod and cap. The latest version is a drilled rod that has a fractured surface between the rod and cap. Drilled, saw cut and fractured rods can be mixed within an engine, but using a non-drilled rod in a drilled application will result in a failure. Special care must be taken to protect the surfaces of the fractured rods. If these surfaces are damaged in any way, the rod must be replaced. (See images below.)
An article in the July-September 2015 issue of Engine Professional magazine (pages 58-62) provided “simple precautions” regarding the use of plugs to stop debris, pre-lube precautions, and the potential for a catastrophic failure with the drilled, saw cut rod bearings.
As mentioned above, the cylinder components have undergone another major design change. Understanding these changes, and which components are compatible is key to a successful repair or overhaul.
History of the liner updates
* Shimmed liners are backwards compatible with all flat top liners and can be mixed within an engine.
** The introduction of a limited number of cylinder blocks released by Cummins in 2010 with a 152mm OD liner diameter was somewhat confusing, and caught a few rebuilders off guard who installed a standard 150mm OD liner into the oversized block unknowingly (see Engine Professional Jan-Mar 2015 for more information). The same piston kits could be used in both the 150mm flat top liners (no shim and shimmed) and the 152mm liner, but the liners are not interchangeable.
This latest change involving the introduction of an APR also requires a smaller diameter and lower top ring design pistons. This affects both the 150mm and 152mm cylinder block engines. The APR liner has a counter bore machined in the inside top of the liner to accept the APR. The APR ring is slightly smaller in diameter than the liner bore. The propose of the APR ring is to scrape carbon off of the side of the piston crown, thus limiting the amount of carbon that can build up on the piston and reduces liner wear and polishing. The APR ring is symmetrical, and can be installed in either direction. The APR ring can be replaced without replacing the liner. A different ring compressor (or adapter) is required to install the piston assembly into these new design liners.
Along with the changes in the liners, pistons have had a variety of updates. Pistons can have open or closed skirts (as shown in the photos below). They can have high or low top ring positions, and the crown diameters can vary. In general, the order of these updates has been from open to closed skirts, from high top ring position to low, and from non-reduced crown diameters to reduced crown diameters. To determine the ring height, measure from the top of the piston to the top of the top ring land (groove). High top ring piston measure approx. 8mm (.315”), and low ring pistons are approx. 11mm (.433”). Reduced crown diameter piston, above the top ring measure approx. 134.86 +/- 0.05mm (5.309 +/- 0.002”) and non-reduced crowns measure approx. 135.30 +/- 0.05mm (5.327 +/- 0.002”).
The chart below outlines the succession and compatibility of the piston and liners. Installing pistons that are not designed to be used with the APR liners will result in damage and/or failure of the engine.
This information is for reference only, and is not intended to be used as a guideline. Please refer to the latest OE service and parts publications for the latest updates and information.
Steve Scott joined the service department at lPD in 1982, working with parts, service and sales for a variety of equipment, diesel, and natural gas engines. Since 2004, he has been the director of product development and technical support for lPD. For more information, email sscott@ipdparts.com.
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