Abstract: A transmission rotatable coaxially about a crankshaft. The transmission is rotatable to three positions: forward, idle, and reverse. Four pulleys are rotatably affixed to the casing such that each pulley occupies the corner of an imaginary square, the diagonals of the square intersecting the longitudinal axis of the crankshaft. The planes of the pulleys all lie in a single plane generally perpendicular to the crankshaft. Thus as the casing is rotated the pulleys rotate coaxially about the crankshaft. Two of the pulleys occupying adjacent corners are driven in opposite directions by gear and/or chain and sprocket means disposed in the casing. The other two pulleys are free turning. The casing pulleys are belt coupled to a pulley on a drive shaft. When the casing is in the forward position, the belt is in contact with one of the driven pulleys and one of the free turning pulleys only. When the casing is in the idle position the belt is in contact only with the two free turning pulleys.