Breach of contract - Used car sale?

[Pyro]

I bought a car recently for $850. The vehicle was not running at the time but the owner assured me that it ran perfectly and there were no engine mechanical problems.
Keeping this in mind, I wrote up a contract when I bought the car that explicitly states that I would be entitled to return of the car and a complete refund if, and only if the vehicle exhibits engine mechanical problems that would normally constitute engine replacement. The limites expressed warranty is only effective for five miles.
The car looked a little shady but I bought it anyway to avoid towing it back at my expense and since I had an expressed warranty (I haven't driven it at all).
After some diagnosis I have found out that the engine is bad, and the owner refuses to refund my money for the vehicle. The contract is unambiguous so much that he doesn't have a leg to stand on in court.

I want to know to what extent I can charge for damages, and what corners can I expect him to try to work to get out of this?

[Wounded Duck]

Good Luck! These kind of contracts are notoriously difficult to uphold. Small claims is your only hope.