I have an older model John Deere LT166 riding mower that engages the blades by rotating a lever to move an idler pulley. The lever will not stay in the engaged position. If I put a lightweight bungee cord on it just as a helper, you can engage and disengage safely, but I wanted to fix it correctly. The belt was very old, so I thought maybe it was too stretched to provide enough tension to stay engaged. I replaced the belt, but it still doesn't stay engaged. Does anyone know if there is an adjustment for belt tensioning that might solve the problem? Is there supposed to be some notch that the arm engages into that is likely worn down? Thanks for any help.