Thank you for using justanswer, and i Greg will assist you with this question .
If you ran the engine dry of oil and now after topping the engine back up and have noticed a knock in the engine , then this is sadly bad news , as the Main or rod bearings will be starved of oil and damage the bearings .
If you are lucky and found this in the early stage, then you may get away with just dropping the oil pan and replacing the bearings ,this is if you have not damaged the main or Rod crankshaft journals .
If you did damage the journals then you will have to remove the engine and repair or replace the crankshaft .
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Kind regards Greg.