The timing gear case houses the injection pump gear, cam gear, oil pump, and the power steering/vacuum pump gear. This housing is also notorious for the dowel pin to slide out and destroy your engine commonly referred to the "Killer Dowel Pin". If your housing is damaged, replace it with an updated Cummins Replacement Timing Gear Housing. This housing features an updated stepped design that will not allow the dowel pin to come through and damage your engine. This is a direct replacement housing and installs using the factory hardware.