32 to move the cam roller 26 along the length of the cam arm 24 referring now to fig2 a rocker arm assembly 10 is shown with the cam roller 26 shown in three different positions designated 1 2 and 3 in fig2 positions 1 and 2 are active roller positions wherein the cam roller 26 contacts the cam lobe 12 as it is rotated by the camshaft 14 position 3 is an inactive position wherein the roller is recessed relative to the cam lobe 12 when the cam roller 26 is in position 3 the valve is not opened as the cam lobe 12 rotates when the cam roller 26 is in position 3 the rocker arm assembly 10 may function as a variable displacement engine control for deactivating the valve the position of the cam roller 26 is changed by rotating the adjustment control shaft 28 as illustrated by positions 1 and 2 the adjustment cam allows for adjustment as indicated by positions 1 and 2 during engine operation as shown in fig2 adjustment between positions 1 and 2 causes the center line of the roller 26 to move an incremental distance represented by the arrows labeled u201c dh u201d that represent the change in height as the roller is adjusted between positions 1 and 2 the adjustment of the roller 26 also causes a change in the timing of valve opening represented by the arcuate arrow designated u201c u03b1 u201d the center line of the roller 26 moves relative to the center line of the camshaft 14 by the amount indicated by u201c u03b1 u201d change in angle when the roller 26 is moved the distance between the center line of the adjustment control shaft 28 and the center.