The versatile John Deere, LA120, 21 HP lawn tractor is available in three mower deck diameters; 42-inch, 48-inch, and 54-inch. Each mower deck can be easily removed when using the tractor for other jobs such as aerating, seeding, raking, hauling and snow plowing. Because of the multi-functional capability of this vehicle, its drive belt may fray, slip or break through heavy use. Fortunately, changing the drive belt on the LA120 is much easier than on some other lawn tractors, where access to the drive belt is beneath the mower deck.
Things You'll Need
15mm socket or closed end wrench
Torque socket wrench and assorted sockets
(2) 1-foot lengths of 2-by-4 blocks
Drive Belt Replacement Procedure
Secure the lawn tractor on a well lit, level surface with motor off and brake set. Place 2-by-4 blocks under the rim on each side of the mower deck. Lower deck onto the blocks by moving mower deck lift lever all the way forward to position #1. Remove the ignition key and use a socket wrench to detach the negative lead from the battery located in the rear of the engine compartment. Keep children and pets away from the work area and never smoke while working on or around any gasoline powered vehicle. Initial removal of the belt from the engine drive pulley should be undertaken from the left side of the vehicle.
Place the open end wrench on the spring restrained idler pulley lock nut located just inside if the black, belt shield and pull clockwise toward the front of the tractor to release tension on the belt. Remove belt from around the large engine crankshaft pulley and release idler pulley nut pressure. To complete drive belt removal, detach the mower deck by disconnecting the clutch cable from its bracket on the left side of the deck and unhooking the spring at the end of the cable from the idler pulley bracket.
Remove the looped locking pins, three on each side, toward the rear of the mower deck; that will release the draft arms and lift links holding the mower deck to the chassis. At the front center of the mower deck, remove the locking pin that holds the supporting rod to free the mower deck. Remove the blocks and pull the mower deck from under the lawn tractor.
Undo the retaining screws on the motor deck belt shields and remove. Loosen the nuts on the two smaller pulleys and the retaining bolts for the belt guides on the right-side pulley. Before removing the old drive belt, make a sketch of the belt configuration. Remove belt and clear mower deck, pulleys and belt guides of all debris before installing a new belt. Although this belt removal explanation only covers the 42-inch mower deck, the 48-inch and 54-inch deck belt removal procedure is very similar. As you install the new belt, be careful to route it inside all of the belt guides, leaving a long loop of belt to rap around the engine drive pulley after reattaching the mower deck to the tractor chassis.
Torque down the pulley nuts to 35-foot pounds and tighten belt guide bolts. Replace and secure the belt shields. Re-hang the mower deck. Attach the drive cable to its bracket and the spring to the idler bracket. Finally, fit the drive belt loop back onto the engine drive pulley by applying clockwise torque to the idler pulley nut in the same manner as was used to remove the old belt.