I've read (without attribution) that if the contact surface is wider than the lobe and placed off-center it will rotate by itself.
Yes/no?
It's that way on every flat tappet cam I've checked. Some cams also have a very slight taper built into the nose of the lobe, but not all of them. Roller tappet cams are flat, since the lifter has no need to rotate to equalize wear. The radiused bottom of the lifter just helps the wear-equalizing rotation happen. I've disassembled engines with sticky lifters with a groove worn across the bottom of the lifter the width of the cam lobe, and the lobe was almost always worn out.
Jerry
