Description

The Cummins ISB Piston Ring Set R-4089404 (1.00 mm oversize) is a precision-engineered replacement designed to restore proper sealing, compression, and oil control in Cummins ISB diesel engines . This ring set directly replaces Cummins OE part number 4089406 , ensuring OEM-correct fitment and long-term reliability in rebuilt engines. Specifically designed for 1.00 mm oversize pistons , this piston ring set is ideal for engines that have undergone significant cylinder boring during professional rebuilds. Each ring is manufactured from high-strength, wear-resistant materials to withstand extreme combustion pressures, high operating temperatures, and continuous heavy-duty operation typical of ISB applications. Precision-machined ring profiles promote quick seating, consistent cylinder wall contact, and stable oil film control. Proper ring sealing reduces blow-by, maintains compression ratios, improves combustion efficiency, and controls oil consumption—critical factors for engine durability and performance. The Cummins R-4089404 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 require dependable OEM-quality sealing performance.