I have a two year old Sears Craftsman lawn tractor with the 42" mowing deck.
It works well with one annoying exception. Almost every time I want to mow,
the drive belt has slipped off of the power take off pulley and is hanging
slightly below it. I have to get off the tractor and reach underneath to fit
the belt back on the pulley. The belt is properly set in that little J-hook
guide thing hanging down on the right side of the PTO pulley. Sometimes it
takes two or three attempts because the belt falls off when I start the
tractor.

Once it engages, it's fine. No slippage, cuts the grass without problems. I
can stop the tractor, disengage the mower drive, and restart with no more
problems. I've replaced the belt with the size recommended in the user
manual but the same thing happens.

Any ideas of why this would be happening?

Paul