The reason for short cycle run times on model engines has nothing to do with heat treating. As the engine runs and comes temperature, the engine heats up unevenly. This is due to many factors; cool fuel flowing thru passages to the combustion chamber, exhaust exiting, and cooling air are some of the reasons. Thus there is great stress put on the engine parts. The heating and cooling of the engine in rather short cycles is done to relieve the stresses.