Cummins engines have many gears. These engines didn't have timing belts or chains, they had gears. A gear on the crank, camshaft diesel pump And hydraulic pump. The gears are what sets the timing for the engine. In general, they are all just press-fit, but some also have keys. Normally they all last a long time, but sometimes they do go bad.

Here are the gears:

  3900633 Gear Housing Bolt
  3901258 Crankshaft Gear
  3907431 Camshaft Gear
  3911331 Injector Pump Gear
  3918673 Timing Gear Housing Cover Gasket
  3918675 Gear Cover
  3931382 P-Pump Gear
  Used 3955153 HPFP Gear
  3960061 Gear Housing Gasket
  3960623 Gear Housing
  5267784 Gear Housing
  Used 5291204 HPFP Gear
  Used Ford 6.4 HPFP Sprocket