The 2-cycle Detroits have been around since WW II or so, in dozens of variants, so parts supply isn't much of a problem. Like all industrial engines, they can be a bit pricey to work on, and fuel efficiency isn't wonderful, but they run forever.
The Detroit engines are 2-cycle, where every upstroke is compression, and every downstroke is power. That's why they're so loud. They fire twice as often as a 4-stroke. As the piston travels down the cylinder it uncovers a set of ports about mid-cylinder and air from the blower scavenges the exhaust fumes out past the valves in the head. These valves, either 2 or 4 per cylinder depending on head design, are ALL exhaust valves! All the incoming air is supplied by the blower, and fuel arrives with the injector shot. The term "Screamin' Jimmy" comes from the siren noise the blower makes, and the fact the engines fire twice as often, adding to the noise!
Jerry
