1974 T100R Daytona. i have removed the clutch, the clutch hub and cover plate exposing the gearbox sprocket. The end play as measured from the threaded end of the clutch end of the main shaft is .07 inches or 1.8mm. Is this within the acceptable range?
Yes, the nut on opposite end of the main shaft did not have a nutlock on it and came loose. The clutch pushrod had worn causing the main shaft nut to rub on the pushrod mechanisms apparently unscrewing it a couple of turns.
I very much doubt that the pushrod had anything to do with it. If the nut was loose, there's your culprit, as TT first indicated. If the pushrod is worn, that is another, and separate matter. A worn pushrod won't cause a loose mainshaft nut, the excess length of the mainshaft as a result of the mainshaft nut coming loose will make it seem like the pushrod is shorter.