O.S.SPEED B2105 Combo Set (OSMG2161)

The O.S. Speed B2105 Combo Set is the fifth-generation member of the B21 engine family, built to deliver steady, high-performance power for demanding off-road racing and a driving feel that remains reliable across varied conditions. Its redesigned cylinder liner and crankshaft promote smooth, linear power delivery, while a lighter outer head enhances drivability and throttle response on rough terrain.

Key refinements include a redesigned 3-port cylinder that boosts mid-to-high end torque by optimizing air-fuel flow, and a DLC-coated crankshaft with revised internal geometry for stronger power characteristics and easier use than the B2104. A lighter outer head further sharpens response, the bearings are ceramic for durability, and a specially treated thrust plate on the cover plate reduces wear between the rotating rod and cover, helping extend engine life.