Cummins Diesel 5.9 Engines : Killer Dowel Pin

The 5.9L Cummins 12-valve diesel engines, manufactured between 1988 and 1998, feature a steel dowel pin that locates the front timing gearcase. Over time, this steel dowel pin can wobble out due to the constant heat cycles and vibrations of the engine. If (or when) the dowel pin works its way completely out, it falls into the timing gearcase.

When the dowel pin falls, one of several things can happen. The dowel pin can: 

  • Fall straight into the oil pan. 
  • It could hit one of the timing gears and shoot out the side of the timing case, creating an oil leak. 
  • The steel dowel pin could jam between the timing gears. This typically causes the cam to break, the valves to hit the pistons, and the engine to internally self-destruct. While this last scenario is rare (a hole in the timing gearcase and a big puddle of oil is most likely), it has happened to many Cummins 5.9 12 valve diesel engines, which is how it got its name-the killer dowel pin (KDP).

Killer Dowel Pin (KDP) Repair

 To repair or prevent the Killer Dowel Pin issue, most of the front of the engine needs to be disassembled to gain access to the timing gearcase. The fan, shroud, overflow bottles, balancer, and lower pulley all need to be removed. With the front of the engine stripped, you can install a small metal tab over the dowel pin to keep it from wiggling out. While you're in there, make sure to tighten up all the gearcase bolts. These bolts loosen over time and will do just as much damage (or more) if they fall into the front geartrain. There is a killer dowel pin repair kit for about $60, which includes a tab, timing cover gasket, and front crank seal to put the engine back together.