Moped Army

I've noticed in one post here that one of the members mentioned that his moped is overheating, and that he can not touch the head, because is very hot.
Is it not normal for one not to be able to touch the head/cylinder of the engine, even if the engine is not overheating?
What head/cylinder temperature is regarded as the point after which the engine is overheated?
I never measured the temp of my bikes, but I'll do that with IR thermometer when the spring comes and I start to ride again.