My 54 a10 stopped on me on a club run on Saturday with an enormous backfire, the timing was checked & found to be well out diagnosis was a stripped fiber gear. This appeared to be caused a worn drive side bearing in the mag however on close examination of the gear it was found that the meshing with idler gear was only about 2/3rds of the full width of the fiber gear. my question is what controls the depth of the meshing? as it is locked on the taper on armature shaft. The premature wear on the bearing is a puzzle too as its only done about 9000 miles, the earth brush is okay.
Can anyone suggest a fix please?