To torque up the axle nut with out removing the pipes use one of these.
Rear Axle 36 mm Nut Ratchet Wrench
The wrench is used to install and remove the rear axle nut on Harley-Davidson motorcycles FL Touring models with 36 mm axle nuts.
• The wrench consists of an extra long ratcheting box wrench with a black vinyl grip and a 1/2 inch square drive for a torque wrench.
• A custom 36 mm double hexagon Flank Drive wheel allows access to reach the application with out the removal of exhaust.
• Loosening and tightening of this nut is a necessary procedure when tightening a drive belt or changing a rear tire.
• Low profile wheel allows access to rear axle nut without removal of the exhaust.
• Ratcheting action speeds installation and removal.
• 1/2 inch square drive allows a torque wrench to be used when tightening.
• The vinyl drip provides a comfortable ergonomic grip and prevents the wrench from scratching or marring the bike.
It's available from Drag Specs, J & P etc but is cheapest from below, you can get a cheap (as in made not price) pressed no ratcheted spanner too. Kastar Hand Tools 9636 Tool - Motorcycle Tools
My FLH manual and handbook as Baza's says check at the slackest spot on the belt and belt adjustment is specified to be carried out on a cold engine.