overhaul engine is a tedious task... only attempt it if u have all the knowledge and tools... if not, better send to workshop.... even at workshop, mechs need to take a few days to complete... its not that easy....
usuali no nid to waste money if ur engine stil ok.overhaul oni when makan minyak hitam n kluar asap putih. change valve seal and grind valve should be enuf. unless kena piston ring then oni u overhaul lo.not cheap leh.