1983 240d engine knock

I have found a 240d that has a knock.I have not heard it . Iwas told by the owner that his x-wife was driving it and it started making a knock so she parked it.Are there any common problems with this engine .Could it be a bad injector, or something else besides bearings.Sorry I do not have more info I have not looked at the car yet .If it is just bearings can you pull the crank and get the pistons out from the bottom or do you have to pull the head.If so do you have to replace head bolts.Any good places to get a rebuild kit from.I plan on running it on straight veggi oil.Can you turbo these engines.