It was the brand and castor that achieved the longest expectancy. No body talked about heat cycling ever. A typical break in for a Fox was to buy a quart of fuel, punch a couple of holes in the cap and run the whole quart of fuel through at a rich four cycle. I recall some Fox's were so tight that you had to put lapping compound in the engine, then turn the crank with a drill.

No one talked about heat cycling or heat treatment till Supertigre came out with their ABC engines. The first ones needed some stress relieving by putting the sleeves in an oven at full blast, then turn off the oven and let it cool down over night. At least that is how I recall it.

I linked articles discussing heat growth and tempering of cast iron. Growth took place just below 1400 degrees F. Tempering at about 600 degree F. Both well below our operating temps.