It was explained to me long ago that if an engine gets too hot, it's at risk of seizing. The reason, as I understood it, was as follows
1) There's a certain gap between the piston and bore. As both increase in temperature, this gap decreases.
2) In the absence of sufficient cooling, this decreased gap will result in more friction, generating more heat, which results in more expansion and friction, etc...
3) Eventually, the gap will be small enough and the temperature high enough that the piston will 'cold weld' to the bore.
I'm revisiting this explanation and starting to question the validity of it. Assuming the piston and bore are made of the same material, won't they grow at the same rate? Why should the gap decrease as temperature increases?