Cat 3116 Diesel Engines [older models] use a mechanical unit injector meaning injection occurs by the mechanical force of the camshaft, pushrod and rocker arm commonly known as the valve train.
This short video will show you where to place the timing tool on the injector and help you understand why that dimension on the injector has to be adjusted to factory specs. The rocker arm adjusted either way will advance or retard the injection timing for that particular cylinder. When #1 cylinder is on compression stroke adjust #3 #5 and #6 injector. Rotate engine 360 degrees [#6 cyl. on compression stroke] and adjust remaining 3 injectors.
***One thing to remember is don't try to move the injector rack unless the spring is slightly compressed [you could damage the injector], there are hold down tools that come with the tune up kit when setting injectors on the engine.
