Cummins is recalling certain model ISB6.7 diesel engines manufactured from February 16, 2010, through May 4, 2012, equipped with fan pulley Part Number 3914462 and installed on certain Thomas Built Buses school buses. The subject fan pulley is part of the accessory drive system on the front of the engine. This system is used to drive such components as the refrigerant compressors, the radiator fan, and the engine water pump. The web of the pulley can fatigue over time, causing the pulley to fail.