Hello SB CJ and PC Most of the differences are listed above,the Phelon flywheel is lighter and is USA made ,it has 3 bolt holes near the centre for removing with a puller.On some mowers eg. Rover,they use a roll pin in one of the 3 holes to locate the starter cup,it's alloy centre has a morse taper.
The earlier Villiers flywheel has the curved cooling fins and has heavier weights attached,made in Sydney under licence by Wipac, it has a steel centre insert with a morse taper and has no bolt holes for removal.
If I have a Wipac flywheel on a Torque-Major motor I prefer to replace it with the Phelon flywheel.
