PaulaJay1 wrote:

The question, why is preheat necessary?

Most aviation engines turn fairly slowly. That allows the manufacturers to use valve
springs that are pretty weak, compared to those in an auto engine. That, in turn,
allows them to build the entire valve train pretty light. That's the weak point in
the design, and you can snap a valve stem if you don't preheat.

George Patterson
If a man gets into a fight 3,000 miles away from home, he *had* to have
been looking for it.