 The idea was dropped, and the bike shipped with a single 18 mm conical seat gold palladium spark plug housed in a copper insert in the rotor housing (NGK A9EFV).The rotary engine places severe thermal stresses on its cases, as two sides of rotor are constantly exposed to high ignition and exhaust temperatures, while the third side inducts cool fuel/air mixture.To cope with this, and probably capitalizing on their previous experience with water cooling, Suzuki opted for a liquid-cooled engine using two separate systems.