Can not get mower belt on

depending on the age of the machine, there could be several possibilities
1-- belts are not tight enough--- belt tension system is not correct, wrong length belts
2--bearings for the shafts for the blades are rusted up and seized - preventing the blades from moving--- switch the machine off , disengage the belt drive and see if you can turn the blades by hand
3--- if you have an electric pto system to drive the belts to the blades then that system is not getting full power to engage the PTO or the clutch is not working--worn facings
take it to a service dealer and have a proper diagnosis done

You most likely have an idler pulley with a bad bearing.

sounds like the wrong size belt or pulley

check routing of the belt also

Even new blades can be out of balance, but my guess would be either the other blade spindle, or the tensioner pulley bearing.

sounds like you smoked a belt check your blade tensioner belt, possibly an idler pulley bearing or your belt jumped off pulley, not getting right tension on belt for blade

Have you check the tensioners? The idler pulleys that are on the arms with springs on them. My reasoning is, if the arms are rusted, or stuck for some reason and not moving freely then the springs can't pull the belt tight. If that's the case, I could see where the belt could be slipping more than it needs to and prematurely wearing out. Just something to check. Good luck.

You'll be working underneath the mower, so it is helpful to raise the mower chassis up -- at least in back. Use your automobile jack, then put jackstands underneath the chassis to do this. Take off the deck drive belt first by releasing the idler spring(s). Unbolt and remove the "anchor" that keeps the PTO clutch from rotating. Disconnect the electrical wires leading to the PTO. Release the tension on the idler for the hydrostatic drive belt. Now you can thread the new hydrostatic belt over the engine pulley and around both wheel motor pulleys. The idler pulley presses it inward to provide tension. Refasten the idler spring - a pair of channellock pliers works well to hold and pull the spring. Now reinstall the wires and the PTO anchor, then the mower deck belt. Good luck! Please rate my answer if helpful, thanks!

I am not sure what type of blade engagement mechanism you have (ex. clutch, tensioner/idler pulley, etc...) but make sure that the blades can spin freely with the belt taken off of their pulleys. It could very well be that one of the pulley bearings is seized.

Electric clutches usually work or they don't. You may simply need a new belt or there may be an idler pulley or blade spindle with a bad bearing causing excessive drag. I have seen idler pulleys go missing altogether causing extra slack in the belt. good luck, Chuck