the new lifter have a ground face (the foot) that can be very ruff this works in then you have a new cam. we would sand the lifters a bit with 600 wet/dry with WD to help them brake in on new cams and not wipe out the cam .with a used cam it has work in the cam with old lifters so just putting new lifters on a used cam would be a very bad idea .a very good way to tear up the cam