The alternator I converted was a Delco 160 amp unit (already on the tractor) with an open back bearing. I got a tach drive kit off Ebay for $32.25 delivered. As others had said; the drive gear had a fine 3/8th thread. The issue here was that the alternator shaft inside the bearing was only .4? and that would have left a wall thickness of .02?. It was much easier to cut the threaded section off the gear leaving about a 1/8? shoulder and drilling out the center and screwing it onto the end of the shaft with an 8-32 cap screw (counter sinking the gear a bit for the screw head). The back of the alternator case didn?t have much to mount the drive housing plate to so the easiest thing was to tap out the brush ?arming hole? to 8-32 (making sure the screw isn?t too long so as to short or break the brush) then drill and tap another 8-32 hole in the shoulder of the unused rear housing mounting hole. The holes in the plate were then countersunk so the screw heads would be flush (The pictures labeled C for countersunk and T for tapped). Since the intended mounting screws now won?t work I just enlarged the case holes and tapped the plate for some 10-32 bolts. There was one nut (for the diode bridge) that stuck out about 1/16th of an inch interfering with the plate so I ground it down a bit (labeled G). The whole thing wasn?t that hard to do and now I?m just waiting for the 3.5? pulley ($19 delivered, Ebay).
