9. Another important part when swapping in a roller cam for a flat tappet in an early engine is a cam thrust button (Comp Cams PN 207). On a flat tappet camshaft, the rotational motion of the lifters keeps the cam from moving back and forth in the block, or “walking” as it’s called. To keep this from happening with a roller cam, this button is installed on the nose of the cam through a hole in the timing set. The roller nose of the button secures against the inside of the timing cover, and prevents the cam from moving around.