The "Killer Dowel Pin", as it is so infamously named, refers to a small metal dowel inserted into the engine block that is used to align the front gear housing during initial assembly. It is located above the camshaft gear and to the left (looking at the front of the engine) of the injection pump gear. The KDP is amptly named because it can have catastrophic consequnces if it dislodges and decends down the front cover. While this pin is found on 12v (6BT) and 24v (ISB) 5.9L Cummins engines, problems associated with dislogding are limited to 12v engines found in 1989 to 1998 model year trucks.
Cracked camshaft gears and/or cracked gear housings are amongt the most common failure points when a KDP becomes dislodged and begins dancing off the complex system of gears keeping the engine running in sync. The best scenario following a KDP event is that the dowel pin gently falls to the bottom of the front cover, eventually settling [peacefully] at the bottom of the oil pan where it can rest indefintely without concern (a screen on the oil pump eleminates the possibility of damage occuring should the pin find its way into the oil pan). The worst case scenario is that the dowel pin becomes lodged between the camshaft and injection pump gears, causing a chain reaction of destruction that includes the pistons meeting the valvetrain and ultimately a catastrophic, unrepariable engine failure.
While affecting all 12v engines, Killer Dowel Pin failures are most common on 1994 to 1998 model year trucks, which utlilze the Bosch P1700 injection pump. The [more desirable] P-pump engines are thought to experience difference harmonics in the gear train and front cover assembly than 1989 to 1993 engines equipped with the VE44 rotary injection pump. Do to the potentially hazardous nature of the KDP, we highly recommend installing a KDP prevention tab on all 12v engines to permentnely eliminate any and all concerns.
A KDP prevention kit is relatively inexpensive insurance against the possibility of a premature catastrophic engine failure. They work by installing a small metal tab over the dowel pin using an adjacent bolt that secures the gear housing to the engine block. Installation of the tab is simple, straight forward, and intuitive. However it requires removal of the front cover, a relatively invasive and time consuming process for those whom have not already experienced the procedure. Some KDP kits include a replacement front cover gasket, while more affordable solutions reseal the front cover using RTV silicon. There is some evidence to suggest that using RTV silicon is advantageous to the factory replacement gasket and may provide a more resilient seal in certain instances. For a closer look at installing a KDP tab, see: 5.9L 12v Cummins KDP Tab Installation Procedures