It depends on the insulation class.
With class A, the hottest spot in the windings can be up to 221F. Class B is 266F. F is 311F and H is 356F.
Most motors these days are either B or F. H is usually for wound rotors, like on generators.
Of course, the outer casing will be cooler than the internal windings. In my opinion, 159F is pretty hot but not necessarily destructive.
