Valve drive mechanism for engine

A valve drive mechanism includes a generally cylindrically shaped tappet assembly (24) comprising a centre tappet (41) and a side tappet (42). The centre tappet (41) has a circular-arcuate side walls (41c) formed with vertical side shrouds (41d) at opposite sides of each side wall (41c) which overlap and slide contact with opposite end guide walls (42h) of the side tappet (42), respectively. When the tappet assembly (24) is in an unlocked state so as to transmit rotation of the side cams (25, 27), the vertical side shroud (41d) of the centre tappet (41) slide on the vertical side walls (42h) of the side tappet 42 so as thereby to guide slide movement of the centre tappet (41) relative to the side tappet (42).