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how dose the belt go on the mower deck

Mike, Usually there are two belts. One goes around two pulleys, a front pulley under the motor and one on the mower deck. Additionally, there is usually a spring tensioner pulley that rides against the belt to allow it to work and for ease of routing. The second belt goes under the first belt and is routed on a common pulley with the drive belt and both (or all three) of the mower blade pulleys. Here is a crazy looking exploded view of a craftsman mower deck And here is a better diagram of it all put together. I think you can get an idea of belt routing out of this one:

how to put blade belt on modile 917289031.

is this for a deck on a 7000 series 42" cut mower?

How to put 42 inches club cadet mower belt back on