The hydraulic injection system (100) with cam comprises an injection valve (50) housed in a tubular injection nozzle (54), a gap being formed between a valve stem (51) of said valve (50) and the inner surface of the tubular injection nozzle (54) to allow an injectable fluid (58) coming from pressurizing means (10) to flow, while a receiver piston (62) fixed with respect to said valve (50) receives on the one hand the pressure of the injectable fluid (58) to hold said valve (50) closed, and on the other hand, the pressure of a hydraulic fluid (60) to open said valve (50), an injection cam (67) being capable to move said receiver piston (62) via an emitter piston (69) and said hydraulic fluid (60).

A variable timing apparatus, for an internal combustion engine equipped with a mechanical fuel injection pump, includes a tubular extender having a front flange bolted to the normal injection pump mount and a rear mounting flange bolted to the injector pump. The timing drive shaft is equipped with a male right-hand helically-splined drive. The injection pump drive is equipped with a left-hand helically-splined drive. A spring-biased, slidable coupler has a front end right-hand helically-splined socket that engages the male right-hand drive, and a rear end left-hand helically-splined socket that engages the male left-hand drive on the injector pump. After engine startup, oil pressure moves the sliding coupler axially rearward and rotates clockwise with respect to and as seen from the timing drive shaft. The injection pump drive also rotates clockwise, with respect to the coupler, thereby advancing injection timing.