I have a Yard Machine with a MTD 42" deck. I replaced the PTO belt when the original one became worn. I used the manual & part no. to buy the new belt at a lawn & garden dealer. The new one keeps falling off. I've worn the manual out by referring to it to be sure I have it on correctly......still falls off. Doesn't seem to be a place to adjust anything on the deck. Belt appears to be 2" too short but everyone says it is the correct belt? Help!

Provide the model number and s/n of the MTD mower?

If possible the brand and model of the belt you bought.