1. While not original , some folks are declaring some NHT cams as EN40. Novil mentions their cams are EN40.
2. The Norton Workshop Manual states the cams are EN32B
"EN32B is a
carbon case hardening steel. Components when carburized have a core strength range of 430-490 N/mm2, with a hard-wearing surface. It is a popular case hardening steel grade for general engineering, readily machinable and weldable in its supply condition. EN32B is low tensile steel suited for lightly stressed components."
3. Some new cams are chilled iron which have their own short comings besides not being the original material. These can be brittle and break if made poorly..Rod Rayborn had one go bad and split exactly on the forge parting line, which coincidentally is exactly in line with the first lobe (RH exhaust).Rod's cam split from installing the Rita EI rotor. I have also been made aware by owners that the cam nut can break off the threads if tightened to the normal required torque.
4. Some declare the cams are nitride treated, which is new? Systematic investigation into the effect of nitrogen on the surface properties of steel began in the 1920s.. .This would be more appropriate on crankshaft cheeks which are EN19.
It has been told that the possible (inappropriate) nitriding of LATE cams during the bankrupsy failure of Norton on late 74 and 75 on EN32B cams is cause for butter soft cams, which I personally have tested and verified. A MKIII is noticeably different than prior 06-1084 twin chain cams.
NHT CAM HARDNESS
results of cam hardness testing
