I saw another post regarding this a month or so ago. I used a square and marked the ends of the play on the sidewall. There's just at two inches on mine and I think the other poster said about 2.25 inches on their wheel.
I don't know if there are additional reasons for the play, but three that come to mind are:
1) Metal expands as it is heated. You don't want metal-to-metal contact, which would just grind down the gear teeth, so the tolerances for gear play have to be big enough to take the thermal expansion into account.
2) There needs to be room for lubrication between gear teeth.
3) Helical cut gears in the final drive, which change the rotational axis 90 degrees, have more play in them than straight cut gears.
Once the gear train is under load almost all of the play is "taken up" and does not present any issue.
A forum community dedicated to BMW Luxury Touring motorcycle owners and enthusiasts. Come join the discussion about performance, modifications, classifieds, troubleshooting, maintenance, reviews, and more!