I have a suzuki khyber with a Cultus carburetor enigne. It was making weird noises as if someone took its silencer off. I got it checked from a mechanic and he said that the car has work in crank( it is cracked) and tappet and a hefty estimate of 20k. It gave no indication of trouble like reduced oil, heat up etc. I daily check its water level and that is not reduced as well. I have also observed black oil (although I filled in a quarter liter of oil on the advice of same mechanic just a week ago). I know the oil is due to be changed but I am confused because if the engine does indeed need that work my money on oil change will be wasted. The car is running with the same loud noises for over 2 weeks now. Please help