How to Replace John Deere LT166 Spark Plugs

Like your car, truck or SUV, your John Deere LT166 lawn tractor needs a tune-up occasionally. Part of the tune-up process includes removing and replacing the spark plugs. When you start the engine, it transfers an electrical charge to the cylinder, where it completes the combustion process. This is how the tractor runs. If you are hearing a miss in the engine when it is running, chances are there is a problem with the spark plugs and you need to replace them.

5/8-inch spark plug socket
Ratchet
Feeler gauge

Instructions

- 1
  Allow the John Deere LT166 to cool down before you begin if it was running. Open the engine compartment by unsnapping the clips and lifting it toward the front of the lawn tractor.
- 2
  Locate the spark plug wires at the front of the engine. Pull the wires off the spark plugs one at a time. Remove a spark plug from the engine by turning it counterclockwise with the spark plug socket and ratchet.
- 3
  Check the gap on the new spark plug using the feeler gauge. The gap should be 1 mm, or 0.040 inch. Install the plug on the John Deere engine. Start the plug by hand, turning it clockwise.
- 4
  Tighten the spark plug using the spark plug socket and ratchet until it is snug. Do not over-tighten the plug or you will strip the threads in the cylinder head. Attach the spark plug wire to the plug by pushing it on until it snaps into place.
- 5
  Repeat the procedure for the other spark plug. Close the engine compartment. Start your John Deere LT166 lawn tractor to test the new plugs.

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