Concentric camshaft with varying wall geometry and method of assembly

A method comprising:

• locating a first lobe member of a camshaft on a first shaft, the first shaft including an annular wall that defines a first bore, the annular wall including a first portion having first radial inner and outer surfaces and a second portion having second radial inner and outer surfaces, the locating including the first portion of the first shaft being located within a second bore of the first lobe member;
• locating a second lobe member on the first shaft including the second portion of the first shaft being located within a third bore of the second lobe member;
• and
• applying an outward radial force from within the first bore that displaces the first radial inner surface radially outwardly relative to the second radial inner surface and displaces the first radial outer surface radially outwardly relative to the second radial outer surface.