thats what i think too, the bearings and the high RPM,as well as the properties of the fuel. Paul what past engines are you reffering too?
Could you give the make and models?
I think its posible to make glow engines that will work with low oil, but at the expense of power and higher price tag.
The biger glow engines from SuperTigre need only 10% to run.
ORIGINAL: RCPAUL
I think it is because of the bearings and the RPM that is produced. I'm sure someone will respond that knows the details. However, there have been glow engines in the past that had needle bearings and used very low oil in thefuels.
Paul