A standard ball bearing will take about half of its rated load as a thrust bearing..The small amount of thrust our airplane engines make doesn't come anywhere near what the bearings could take..US and Quadra 35 and 41 engines have roller bearings, the thrust is taken up by a bronze thrust washer..Many small glow engines have bronze bushings and work just fine....I think someone at Fox engines once said there was no difference in the performance of the bushing engines, just less weight.....