(1) Remove the gear case cover
(1)Use socket and put on crank gear nut and turn engine (clockwise) till #1 piston is on TDC on compression stroke.
(3) Inspect the gear timing marks
(4) There will 3 marks on the idler gear that will align with the cam gear, the crank gear and the injection pump gear. (there may be one on the oil pump and aux drive gears also but if not disregard them as they will not matter on their position)
(5) Of those 3 marks they may be labeled 11, 22, and 33 or 1, 2 and 3. mark 1 goes toward the crank gear, mark 2 goes toward the cam gear and mark 3 goes toward the injection pump gear.
(6) Check the mark on the injection pump mounting flange and make sure it is aligned with the marks on the mount plate flange, if there are 3 lines align it with the center line.

Once all the marks on the gears align up the engine and injection timing is set.

reinstall the cover

Now if you have not disturbed the cam and crank gears and have just replaced the injection pump just make sure the engine is on the TDC on compression stroke and use the timing mark 3 on the idler gear and set the injection pump gear mark on it. Also make sure the outer mark is aligned with the center mark on its flange against the flange mount plate.