Joe, the old way to break in the OS two strokes was to just fire them up, set the high end, set the low end then fly the plane. We would do a gang of BIG loops and stall turns. Going vertical would heat the engine up and going down would cool it off. Very easy and worked very well, the engines were broken in after a couple of tanks. I have been told the new OS engines are made with a lot of different metals and require more break in time and the old way of doing it in the air isn't the best way to do it anymore. I'm sure Bill Baxter has writen something about it in the engine forum. I no longer do a lot of work or use a lot of the two strokes so it would be nice to see what Bill has to say about this. I do know that I too really like the AX line and find them very user friendly but I could say that about all the OS engines I have used over the years.