Scag, a manufacturer of several different models of zero-turn lawnmowers, utilizes a single drive belt to connect the output power from the engine to the mower deck's cutting blades. Scag equips its mowers with a pulley system that consists of one engine-mounted pulley, two idler pulleys and two spindle shaft pulleys that run the mower deck blades. When the pulley stretches, it reduces the speed of the blades by allowing slippage. When this happens, you need to replace the belt.
Disengage the mower deck if it is currently engaged by placing the throttle at 3/4-full then pressing the "Mower Deck Engage" button located on the left-most control panel. With the deck disengaged, throttle down the mower and turn it off.
Set the parking brake to ensure your Scag mower does not move while you work on it. With the deck at the standard cutting height, you can access the belt system.
Make a diagram of the belt routing before you start to remove the belt. This ensures you get the new belt on properly.
Rotate the belt manually around the pulley at the bottom of the engine. Pull down on the belt to slip it off the pulley while you turn it.
Push the belt past the belt guard as you push the belt toward the mower deck. Remove the belt from the pulleys on the deck.
Place a new belt onto the pulley system on the deck and make sure you position it between the pulley and the belt guards by the pulleys.
Slide the belt past the belt guard then slide the belt over the pulley mounted on the engine. You may have to rotate the belt while you push it into position.