2002 ford focus 2.0l sohc blowing white smoke and loud noise like a knocking from the bottom of the engine or/and rough idle,what could cause these

If a vehicle is smoking then it is obviously burning oil, loud noises from bottom of engine usually indicate main bearing failure, but that wouldn't usually make smoke are you sure it is from bottom of engine. Sounds more likely to me that you have either valve or piston problems, a valve seal gone would result in smoke as oil leaking into Cylinder chamber would burn producing smoke. Piston ring failure would also produce smoke and most likely a significant loss of power with possible noises resulting from broken pieces of ring in the cylinder impacting on head, this may have also unseated a valve causing the smoke. To check ring or valve failure you need to do a compression test, to check for bearing failure I am afraid it will require inspection either by removing sump pan ( oil pan) and removing bearing covers to check for damage.Whatever the cause it sounds as if it may be quite expensive and age and condition of vehicle should be taken into account, after all with the cheap cars on ebay it may be more cost effective to cut your losses and replace the vehicle. If a vehicle is smoking then it is obviously burning oil, loud noises from bottom of engine usually indicate main bearing failure, but that wouldn't usually make smoke are you sure it is from bottom of engine. Sounds more likely to me that you have either valve or piston problems, a valve seal gone would result in smoke as oil leaking into Cylinder chamber would burn producing smoke. Piston ring failure would also produce smoke and most likely a significant loss of power with possible noises resulting from broken pieces of ring in the cylinder impacting on head, this may have also unseated a valve causing the smoke. To check ring or valve failure you need to do a compression test, to check for bearing failure I am afraid it will require inspection either by removing sump pan ( oil pan) and removing bearing covers to check for damage.Whatever the cause it sounds as if it may be quite expensive and age and condition of vehicle should be taken into account, after all with the cheap cars on ebay it may be more cost effective to cut your losses and replace the vehicle.