How to Change a Lawn Tractor Pulley Ratio

Changing a lawn tractor's drive pulley diameter changes its pulley ratio. The drive pulley on a lawn tractor's mower deck is the pulley that remains on the tractor when the deck is removed. Mower decks have a pulley for each blade. Making a ratio change via the driven pulley requires changing multiple pulleys. If the drive pulley diameter is 6 inches and the driven pulley is 3 inches, for example, then divide 6 by 3, which results in 2; that means the driven pulley turns twice for every one turn of the drive pulley, and the pulley ratio is 2-to-1.

Safety glasses
Jack
Jack stands
Tape measure
Sandpaper
Penetrating oil
Allen wrench set
Gear puller
Larger or smaller diameter drive pulley

Instructions

- 1
  
  Safety is important. Lawn tractors do not support two riders safely.
  
  Remove the mower deck from the lawn tractor. On most models, the mower deck has four latch pins located on top of the deck, and those latch pins must be removed. With the pins removed, the mower deck drops down and can be slid from under the tractor. Consult the service manual for specific instructions to remove the mower deck on your tractor.
- 2
  Raise the lawn tractor with a jack, and place jack stands under the vehicle's frame for safety.
- 3
  Locate the drive pulley. It is the pulley that powers the mower deck in summer and the snow blower, if applicable, in winter. Measure and record the vertical distance from the center of the pulley "V" to the frame of the tractor. The V is the groove around the pulley where the belt rides.
- 4
  Clean rust off the pulley shaft with sandpaper if the rust extends from the bottom of the pulley. The pulley should have at least one and possibly two set screws that are countersunk into the pulley hub and tightened against the pulley shaft. Spray penetrating oil into the set screw holes.
- 5
  Insert an Allen wrench into the set screws, and loosen and remove the screws. Spray more penetrating oil into the empty set screw holes and around the top and bottom of the pulley shaft.
- 6
  Center a gear puller on the pulley shaft, and attach the puller to the pulley. Tighten the puller center bolt until the pulley is removed from the shaft.
- 7
  Install a larger diameter drive pulley to increase the speed of the mower deck or snow-blower, or install a smaller diameter drive pulley to decrease the mower deck or snow-blower's speed.
- 8
  Raise the lawn tractor off the jack stands, and remove them. Place the tractor back on the ground.

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