One problem with CVH engines are the cam and tappets, they wear together, so changing one or the other is useless. it NEEDS to be a brand new cam and tappet set, OR a 2nd hand cam, with the tappets in the correct order of removal.

If your RSI has hydrualic tappets fitted, and it is a genuine 16i engine (I dont know how to tell) then it could be someone has stuck in a set of hydraulic tappets and left the original cam in, and now the tappets are knackered?

probably worth checking the cam and tappets, to see what the score is, and take it from there.

Also check the rocker studs in the head, these can be pulled out the head which is fairly common, nothing a wurth insert/helicoil wont sort.

HTH