The interface/interaction of the roller wheels and the camshaft can generate substantial thrust force....... either forward or backward.
For any particular build, you won’t really know if there is any, and if there is, how much there is, or in which direction.
So, to cover all bases....... incorporate some sort of thrust control in both directions, and some form of wear protection for the block.
Frankly I don't buy this. If a thin, stamped steel timing cover with a nylon thrust button can control forward thrust, there is no way that there is substantial reverse thrust. As to the rollers on the lobes, if the lobe face is ground parallel to the camshaft centerline and the rollers are cylindrical, the only way that there could be any thrust in any direction would be from lifter bore misalignment. To say this produces greater reverse thrust than the taper on a flat tappet cam that by design imparts substantial reverse load.... Again, I don't buy it.
