Description

The Cummins ISB Piston Ring Set R-4089402 (0.50 mm Oversize) is a precision-engineered replacement designed to restore proper cylinder sealing, compression, and oil control in Cummins ISB diesel engines . This ring set directly replaces Cummins OE part number 4089405 , ensuring OEM-correct fitment and dependable long-term performance. Specifically designed for 0.50 mm oversize pistons , this piston ring set is ideal for engines that have undergone light cylinder boring during professional rebuilds. Each ring is manufactured from high-strength, wear-resistant materials capable of withstanding extreme combustion pressures, elevated operating temperatures, and continuous heavy-duty service typical of ISB applications. Precision-machined ring profiles promote fast seating, consistent contact with cylinder walls, and stable oil film control. Proper ring sealing reduces blow-by, maintains compression ratios, improves combustion efficiency, and controls oil consumption—key factors for engine reliability and longevity. The Cummins R-4089402 piston ring set is commonly installed during ISB engine rebuilds, in-frame overhauls, and professional remanufacturing projects . It is trusted by diesel technicians, fleet maintenance teams, and engine builders who demand OEM-quality sealing performance.