I was talking to a retired guy who spent most of his working years in a motor/generator rewind shop. He explained that he could look at motors and generators an accurately judge which one would never come back for a rewind. There was a direct correlation between mass and the KW or Horsepower rating. The heavier the motor, the less likely it was to need rewinding.

I have thought about this and think the cast iron helps to keep the temperature more constant than the light weight frames. The more rapid heating and cooling probably helps break down the insulation in the windings. Heating expansion creates movement, so it would stand to reason that it doesn't help matters, the higher the mass, the slower the movement... this is also a good thing in electrical and electronic circuits.

ST style heads shouldn't be your first choice if you are going to take it camping and expect to haul it out of the trunk of your car.  But if you are looking for stationary power, or something to mount on wheels,  something simple to work on and easier to understand, this may be for you. If you're in search of the most technically advanced generator... keep looking.