Justo, do you mean camshaft timing, or ignition timing?

Because the ignition timing is fixed (set by the flywheel key, in other words) I'm guessing you mean the camshaft timing. This is covered in nauseating detail in Section 10 of the Service and Repair Instructions, 1984, but until you get access to them you can view the same book on line, here:
http://recoveryvehicles.tpub.com/TM-5-4240-501-14P/css/TM-5-4240-501-14P_238.htm

Just use the "next" button at the top of the page to work your way through the chapter.