The cam gear is secured by a taper to the cam. There is no key way to align the two together. It can be mounted in any orientation of 365 degrees to the cam. Thats the reason the mark on the cam does not line up with TDC (its not a tdc mark) It also also allows you to run any cam timing you want as the cam can be degreed to any CLR you want just by re orienting the gears on the taper. The procedure is there for changing cams or replacing cam gears, its also the only way to ensure the gears have not slipped on the shafts (it happens). a degree or two makes a difference in the cam timing.