The standard setup on Tevo Little Monster Pulley setup means the belts rub constantly against the wheels in the Carriages. Dropping to a 16 tooth pulley on the motor gives enough clearance not to rub from the top but there isn't any M5 16 tooth Idler pulleys so I had to design a solution.
I decided not to bother with the old aluminium holders for the idler pulley as I noticed it flexed when the belts were pulled tight so I decide to use a larger steel plate instead. I have added 2 sets of bearings to pull the belt back inside the carriage wheels and also add 2 additional anchor points. It also has the added benefit of reducing the amount of pressure on the main idler pulley preventing it being warped over when you add the correct belt tension (around 30kg)
For each tower you will need 2x M5 bolts, 2x M5 lock nuts, 4x M4 T-nuts, 4x 10mm bearings and a bunch of washers for spacing.
Measure out the 4 holes along the edge for the anchor points and use a 4mm drill for the holes. Then towards the bottom drill a 5mm hole in the centre and 2 more M5 holes towards the top off centre by about 5mm. Transfer the 20 tooth idler pulley (suggest upgrading to one with teeth) then setup the 2 additional bearing sets making sure you use the correct number of washers to align the new bearings with the old idler pulley.
Tension everything up and you will see the belts no longer rub. I suggest spraying everything down with silicon spray (the type that dries).