On removing and reinstalling the rocker towers,make sure the rockers are not under strain by the camshaft lobes-you need to do the pairs one by one.Also it`s possible one of the pairs be really hard to pull(upwards).There is 1 small centering cylinder under each rocker tower-be careful not to let`em go past the chain into the sump...on istallation observe the correct orientation of the valve springs(it`s advisable to change`em)...
Torque the bolts to 38Nm....then valve adjustment...