I am going to assume that this is a vertical shaft engine. If it is, then the side loading from a belt can wear the bearing surface out of round.
If you have a end play problem, then you have a lubrication problem. Most likely, oil not being changed when needed.
Check the side cover for excessive wear. There is going to be some wear from general use.
There are clearance grooves, around the crank bearing area, to allow lubrication to the the bearing surfaces. With the side cover tight on the block, measure the end play.
These engines will tolerate quite a bit of end play.
If the thrust area is excessively wore, then this area can be welded and filed, milled to take up excessive play.
If the upper or lower bearing bore is wore excessively, they can be bored and a teflon coated sleeve bearing can be installed.
This is how I repair engines for the lawn mower racers and tractor pullers.
Dale Kohler