Any dirt bikers out there? Remember the original Honda Elsinore 125 cc dirt bike? Super light, cheap, and fast for its time--but you had to fan hell out of the clutch at low speed or that sucker would load up like crazy! It was a piston port design (common at that time); the timing for the intake was when the piston skirt covered/ uncovered the crankcase opening. Nice and simple, with massive flow rates when set up for high performance. (Honda used that design for their GP road racing bikes as well.) A dog at low rpms, though.

These were air cooled motors, so the water jacket didn't get in the way, but there's not that much need of a water jacket at the low point of piston travel and on the intake side. And they were simpler than a reed/ rotary valve set up.

Interesting?

Jeff