The spark plugs are easy to spot on the left side of the motorcycle.

The procedure for removing the spark plugs is the same for both the front and back cylinder, and either spark plug can be replaced first. This guide will show how to remove and install the spark plug in the rear cylinder.

Carefully remove the spark plug wire. Do not pull on just the wire, squeeze the spark plug boot, and pull it together with the wire.

Use an 11/16" spark plug socket to unscrew the spark plug by turning in a counter-clockwise direction.

Some aftermarket spark plugs that fit the Sportster use a slightly larger 18mm spark plug socket.

Remove the spark plug from the cylinder.

Always inspect your new spark plugs before installing. Check the gap on your replacement spark plugs with a feeler gauge. It should be set to .040 inches.

If they are not pre-installed, make sure that the crush washer and terminal nut are installed.

Using your fingers, install the new spark plug into the socket, and hand tighten until firm.

Using a torque wrench, tighten the spark plug to the proper specification.

When installing spark plugs, proper torque can be important. To loose and they could rattle out or leak; too tight and you can strip your cylinder head. The correct torque for this plug is between 90 and 120 inch lbs.

Reinstall your spark plug wire by pushing it firmly onto the new plug.

Make sure that it seats properly. You can usually feel a definitive click when it is installed correctly.