Things You'll Need
Set of Torx wrenches
New Troy-Bilt drive belt
Milk crates (2)
Bricks or rocks (2)
The Troy-Bilt 21-inch, self-propelled lawnmower is a precision-made machine powered by a 160 cc Honda overhead cam engine, complete with electric key start ignition. The mower's single speed drive transmission provides ease of use by eliminating the need to push the mower through heavy growth. Although the drive belt is designed to last from season-to-season, when it eventually wears out, you can replace the belt in less than 30 minutes without dismantling the mower deck.
Push the mower onto a paved level surface. Remove the rubber boot from the spark plug and push the ignition lead to one side.
Undo the two knurled shoulder screws on either side of the molded front drive cover manually. Press the sides of the cover inward to release the tabs that secure the cover to the height adjuster brackets. Lift the drive cover off and set it aside.
Stand in front of the mower and locate the screw that holds the belt tension spring to the transmission; this screw is situated on the top right of the transmission beside the right front wheel. Insert a Torx wrench into the screw and loosen it by cranking the wrench counterclockwise one full turn.
Grasp the transmission assembly with your left hand and lift it up slightly. Slide the drive belt off of the transmission pulley fitted to the top of the transmission assembly.
Have an assistant push the mower handle down to lift the front of the mower so that you can access the belt from underneath; if you don't have a friend handy, prop the front wheels up on a pair of upturned milk crates and place bricks or rocks behind the rear wheels to steady the machine.
Line the cutting blade up sideways. Reach under the mower and pull the belt through the open slot on the mower deck. Loop the belt over one end of the blade. Slide the belt off of the engine pulley and pull it off over the other end of the blade.
Loop the new belt over both ends of the blade and insert the V-shaped section into the groove in the engine pulley. Push the belt through to the front of the mower and give it a gentle tug to ensure that the V section is still seated in the engine pulley groove.
Lower the front wheels onto the ground and lift the transmission assembly slightly while maintaining tension on the belt. Loop the belt over the transmission pulley. Tilt the mower and double-check to ensure that the belt is still seated in the engine drive pulley groove.
Tighten the belt tension screw that you loosened earlier with the Torx wrench. Replace the front drive cover and push the sides in to snap the tabs back into the height adjuster bracket. Replace the two knurled shoulder screws and tighten them firmly by hand.
Reconnect the spark plug lead. Start the mower and engage the drive lever to ensure that the transmission is working properly.
Protect your hands from the sharp cutting blade by wearing heavy work gloves before pulling the worn drive belt off of the engine drive shaft and replacing it with a new one.