Hi all, just when do you need to change the timing/cam chain on a petrol 1.8 04 Tino ,have done 46,000 and it runs fine , a mechanic said i should change when it hits 50,000 ,but do you get any warning signs before it needs doing and is it easy'ish to check it out at all ....am strapped for cash so a big bill would take me under !!!