What are my options by law, barter trade car for car as is contract, going bad?

[Ricardo]

I traded my car (94 civic ex) with extra accessories for another car (acura legend 93) Straight up no cash just barter, bill of sale was signed by both parties with as is contract. Titles are not signed over yet cause of different schedules. I gave him the car in good running condition since then he came to me with a issue that occurred with the engine, He admitted to me he ran the car with no oil and now is hearing a knocking sound in the engine. The son that signed bill of sale is not owner of title, his fathers name is on title. Now his father wants cash on top of barter trade, both cars need money put into them. What can I do if father does not want to sign title over, after son has signed bill of sale as is and told me his father would sign over the title. I also spoke with father and he previously agreed to sign over title with no cash. If i accept the civic back, I will have to buy a new engine, that I dint damage, What are my options by law?