Truck Repair: WHAT IS STC, hydraulic tappet, bellhousing

Question
THANK YOU FOR THE INFO BUT WHAT IS A STC ENGINE AND HOW DO I KNOW IF I HAVE ONE OR NOT THANKS J.C.

Answer
STC is Step Timing Control.It changes the injector timing with a hydraulic tappet in the top of the injector to advance injection at low speeds.You can tell if you have one by a large(#10) oil supply line in the rocker housing around #5 cyl on the fuel pump side.Usually you can not se the control valve because it is mounted next to the bellhousing on fuel pump side on the main oil rifle mid ways the block.