Cummins 3971603 Starter Motor Assembly

The Cummins 3971603 is a 12-volt, 3.0 kW offset gear reduction (OSGR) starter motor featuring a 10-tooth pinion with clockwise rotation. It is engineered for direct-fit installation on Cummins B-series and ISB/QSB 5.9L and 6.7L diesel engines. The unit utilizes a solenoid-shift engagement mechanism and permanent magnet or field coil construction typical for heavy-duty commercial vehicle starting systems. Designed to meet OEM cranking torque and durability requirements for cold-weather starting in Class 7-8 truck applications. This starter assembly replaces Cummins OEM part number 3971603 and cross-references to Denso manufacturing part number 428000-2860. Primary applications include Cummins 6BT5.9, ISB6.7, and QSB6.7 engines installed in heavy-duty trucks such as the Dongfeng Tianlong Flagship series. The component is validated for 12V electrical system compatibility and standard SAE flange mounting configuration.