[Slowcoach]

4.4 If an approved type/range of motor is changed in any substantial way, it must be resubmitted for approval, and must be available at retail outlets incorporating such changes. Examples:- can colour, label design, brush dimensions, orientation of the brushes or design change of end bell assembly major components. This will include any design changes or additions to the armature or commutator by the manufacturer.Addition or removal of screw-fixing heatsinks is allowed. Change of end-bell colour is allowed providing all design features are maintained.

Having changed a bonded for a sintered rotor, I can tell you that they are two completely different items.

I have seen that Novak are going to go all sintered. If that is the case and their motors are resubmitted, with no other changes, then there is no reason why you can't retro fit a sintered rotor (to the Novak at least).