A straight-two engine, parallel twin or inline twin's a two-cylinder piston engine that's its cylinders arranged in a single row. There're two primary crankshaft configurations for this engine with a new third configuration. One has both pistons moving identically (360° offset) and's commonly called parallel twin. An inline twin or straight-two has one piston moving up as the other moves down (180° offset). The third and new concept offsets the pistons 90° from each other similar… (More on Straight-2)