Does anyone have conversion parts, or details of exactly what John McDougall did to modify his gearbox? It may be possible to deepen the cam-plate notches somewhat, but there appears to be limited clearance for a long-travel index plunger.
The AMC-Norton gearbox uses semi-circular lobes instead of relying on simple notches on the perimeter of the cam plate. It also needs a long-travel index plunger. I hear that earlier Norton boxes can be modified to take the AMC camplate, you have to machine the casing on the inside for clearance.
The Norton box has a lot of history in it. The Sturmey Archer motorcycle racing 3 speed of the twenties had ratios 1:1, 1:1.33, 1:1.78. (The Manx Norton kept these ratios to the end, with the addition of an extra gear below top, of 1:1.1). Those gear ratios are exactly the same as the classic Sturmey Archer 3-speed bicycle hub gear of the '20s to the present, from K series, through AW in its many iterations. I have not got the figures to hand, but if my memory is correct that second is 24:18 teeth, then the AMC1 box of the late '50s has these exact same ratios but with a 2.7:1 first gear.
The AMC-Norton gearbox uses semi-circular lobes instead of relying on simple notches on the perimeter of the cam plate. It also needs a long-travel index plunger. I hear that earlier Norton boxes can be modified to take the AMC camplate, you have to machine the casing on the inside for clearance.
The Norton box has a lot of history in it. The Sturmey Archer motorcycle racing 3 speed of the twenties had ratios 1:1, 1:1.33, 1:1.78. (The Manx Norton kept these ratios to the end, with the addition of an extra gear below top, of 1:1.1). Those gear ratios are exactly the same as the classic Sturmey Archer 3-speed bicycle hub gear of the '20s to the present, from K series, through AW in its many iterations. I have not got the figures to hand, but if my memory is correct that second is 24:18 teeth, then the AMC1 box of the late '50s has these exact same ratios but with a 2.7:1 first gear.
