Overview: The B2105, which has evolved into the fifth generation of the B21 series, is designed to secure power that gives an advantage in harsh off-road racing scenes, and pursues a driving feel that steadily demonstrates performance in any situation. By re-designing the cylinder liner and crankshaft, we have achieved smooth and linear power delivery. Furthermore, the effect of a lighter outer head successfully improves drivability in any situation. Cylinder The newly designed cylinder and liner applies 3 ports. The port shape has been changed and the air-fuel mixture flow has been reviewed to achieve more torque from mid to high end. Crankshaft The modified crankshaft has undergone O.S.SPEED's traditional DLC coating and the internal shape has been revised to improve not only power characteristics but also easier to use than B2104. Outer Head Drivability is improved by reducing the weight of the outer head. Bearings Inherited from the well-established B2104 crankcase. The bearing inside the case also uses a proven ceramic bearing. Thrust Plate By adopting a specially treated thrust plate for the cover plate adopted from B2104, wear caused by friction between the rotating connecting rod and the cover plate is reduced and engine life is impiroved.