I'm having trouble getting the upper belt on the deck snug. We took the deck off last night because only one of the blades were turning, so the lower belt had to be replaced. We got the deck back on, but the upper belt isn't snug. It looks about 2 sizes too big. Any clues what we might be doing wrong? If I could find the digital camera I would post pics. Mower: JD LT166 Deck: Freedom 42" Thank you in advance.