downwardly the shut off valve 42 will be switched so as to shut off the motor to the rotatable blade thus stopping the blade from being rotated and preventing possible injury to the operator turning now to fig3 6 the biasing mechanism 40 includes a cylinder 44 and piston 46 assembly secured to the top portion 28 of the housing 20 the cylinder 44 and piston 46 assembly may be hydraulic as shown the piston 46 has a working end 47 pivotally connected to a first end 62 of a bell crank 60 a second end 64 of the bell crank 60 is pivotally attached to the side panel 30 via a connecting arm 66 the connecting arm 66 has a first end 67 pivotally connected to the second end 64 of the bell crank 60 and a second end 68 pivotally connected to the side panel 30 the bell crank 60 has an elbow 61 that is pivotally secured to the housing 20 as shown the elbow 61 is pivotally connected to a mounting member 29 extending from the top portion 28 of the housing 20 the elbow 61 is positioned proximate the shut off valve 42 the shut off valve 42 is secured to a motor casing 23 extending above a top portion 28 of the housing 20 the.