The present invention relates (with reference to Figure 1), to a valve operating mechanism for operating a poppet valve (10). The mechanism comprises: a cam (13) mounted on a camshaft (14); a first rocker (15) which is pivotally mounted on a first rocker shaft (17) and which is driven by the cam (13) to pivot in an oscillatory manner; and a second rocker (16) which is pivotally mounted on a second rocker shaft (21) spaced apart from the first rocker shaft (17) and which engages the poppet valve (10). As the first rocker (15) pivots the follower member (27) moves relative to the cam surface (30) and relays camming action of the part of the cam surface (30) engaged by the follower member (27) to the reaction surface (31) and thereby causes the second rocker (16) to pivot and impart motion to the poppet valve (10). A control mechanism (28, 29) can move the follower member (27) relative to the cam surface (30) in order to vary which part of the cam surface (30) is engaged by the follower member (27).
