a multiple spindle mower deck within which a plurality of mower blades rotate for mowing grass and having spindle housings which rotatively support respective mower blades , the spindle housings being operatively rigidly fixed with the mower deck . a belt drive mechanism drives the spindles , and includes pulleys mounted to respective spindles and a belt which operatively engages the pulleys . at least one idler pulley engages the belt . a mounting plate is provided to which said at least one idler pulley is mounted . the mounting plate is operatively fixed with the spindle housings , position above and press into abutement with the upper surface of the top wall of the mower deck by way of the same bolts which fix the spindle housing to the mower deck . the spindle housings are fixed to the mower deck by the spindle housing bolts which operatively press the spindle housings deck and mounting plate together . one of the idler pulleys is a tensioning idler which engages the belt for placing tension in the belt , and a tensioning mechanism operatively engages the tensioning pulley for applying a force to the idler pulley . the tensioning mechanism is mounted to said mounting plate .