remove the cam cover, the cam belt and undo the cam shaft shells,

remove the tappets with a valve lapping in suction tool (NOT A MAGNET)

leave them soaking in degreaser for a day and work the piston underneath with a pair of pliers, in and out many times holding the hole in the side of the tappet under the level of the degreaser - lots of thick mingin old oil will ooze out. leave them soaking another day and repeat. one all free, you will fell the piston move really lightly with hardly any resistance. pump out the degreaser, and then leave soaking in new synthestic engine oil for a day and pump them under the level of the oil and repreat the next day. then refit - they will rattle a bit the first 20 secs of engine running. stop the engine and let them recover for a few seconds and start again, this may take 3 or 4 goes and then they will be whisper quiet.