an easy hint...
white smoke when acceleration..valve seals worn out.
if thick smoke emitted by exhaust pipe even at idle...he he its the piston and ring.
if latter is common to u, change engine laa...becoz overhaul is costly.
but normally , under normal ciscumstances if the engine is less than 10 years old (or about 200,000km maybe higher u only need to do top overhaul @ also known as grind valve (or grembal by mekanik pokok ceri). as u had removed the cylinder head from main block, feel the cylinder liner. if top portion thicker than the sidewalls...its advisable to change piston ring set. not necessary piston itself. the mechanic shud know this.
to be precise, use the proper equipment to measure whether the said components are still within their clearance spec. otherwise, change.
p/s or change to 4G91..he he..