When building something like the "Phoenix" with it's 50BHP engine there is a need to uprate the clutch .
The main problem with the original design is the thin steel outer plate which becomes bowed out by the spring pressure , so that the friction plate is only gripped around the outer edges considerably reducing it's power transmitting capabilities.
To overcome this the "Phoenix " clutch has a cast iron outer plate 0.375 inches thick machined from a Fiat "Uno" front brake disc , this is much stiffer and also has better frictional properties than steel . In order to keep the rotating weight about right the main flywheel is machined down to the bottom of the counterbores for the six studs .
The friction disc that I used was from a Bedford CA van 1952-1964 part number HB-9583 , this does not quite fit directly but must be modified as follows :--
Turn the overall diameter to 173.0 mm .
Bore the centre of the spline to21.0 mm .
Face off the inner side of the splined centre to within 1.0 mm of the torque spring retainers .
Finally six 19.0 mm diameter buttons were riveted to the back of the pressure plate on a 155 mm PCD to locate the free ends of the springs , this prevents them from flinging outwards and binding on the holes in the flywheel , which reduces their effective force while at the same time making the clutch harder to lift .
