also, dont know how true it is, the cam shift sits a little too high and the engine cant properly lubricate it in idle.
The cam/rollers are lubricated by excess oil coming off the lifters from the lifter bores, there's no way for rod bearing splash to get on the cam because a huge chunk of the block is in the way.
This issue appears to have emerged when variable cam timing was added to the HEMI, prior HEMI engines, with MDS and without, didn't suffer from it, which throws the theory about there being a design issue component to it, out the window.
Both the lifters and the camshafts were revised (supplier likely changed) around this time and my impression is that quality took a nosedive. The SADI camshafts can be an issue all by themselves, but the primary failure mode tends to be a lifter packing it in. In both instances, the problem is improper hardening, which both the SADI cams and the roller lifters depend on. The lifter pin and roller are both surface hardened, as are the camshaft lobes.
According to our resident FCA tech,
@TeamZero, the pin or the roller heat treating is defective on the ones that fail, and is subsequently breached at some point. Once that happens, the surface starts to wear and eventually a small "ditch" forms in either the pin or the roller. Once the ditch gets large enough, the needles eventually pile-up and the roller stops rolling, rapidly wearing away the camshaft lobe, whose surface hardening is also rapidly breached by the roller sliding, rather than rolling, on it.
We have also seen some examples of improper surface hardening on the SADI cores and pitting happening, but the rollers are still rolling at that juncture. This seems to be less prevalent.
Issues with both roller lifters and SADI camshafts are not exclusive to the HEMI. The Pentastar has had similar camshaft and roller issues, despite being DOHC, and Honda has had SADI camshafts failing in the same manner. GM uses billet cores, but lifter failure with the AFM engines is even more prevalent than with the HEMI. As
@Rod Knock noted, Ford is also having lifter failures on the 7.3L. All of this is likely the result of these components being offshored, as during the 80's, 90's and early 2000's, roller lifters and camshafts were "lifetime" components that never failed.