A number of possibilities here
Is it an LA series motor? (OS - 40LA). They have plain bushings as bearings and some of them do have a bit of end float on the crank which is usually not a problem.
If it a ball bearing motor, the end float certainly shouldn't be there - change the bearings now before they self destruct any further.
The propellor or the spinner could also be out of balance.
Is it a new motor or a second hand one?