This is the OS B2103 Type R engine. This 5-port long-stroke engine offers great power at medium-high speeds. The crankcase, the crankcase cap and the carburetor feature a new design. The new DLC-coated crankshaft has two tungsten counterweights for smooth rotation and better balancing. It shares the same new features as the Type S engine except the cylinder and the cooling head which has a standard round shape.