Pain threshold for most people is 50-55C, so that sounds like a pretty modest temp rise. The motor label will tell you the "insulation class" which is most likely "B" (130C) or possibly "F" (155C) or even "H" (180C). If you can touch it with your hand you have nothing to worry about. Motors that are intended for continuous use at low speeds often have a cooling fan attached but I wouldn't worry about it myself.