I sold a used snowmobile to a guy and it ran fine, he blew up the motor the next day and wants his money back.?

when he bought the sled it ran fine, he took it for a ride and he had no complaints. the next day he said it went 4 miles then smoked a pistion and wants me to pay for the repairs. The sled was sold as is and had good compression when i sold it to him. Am i responsible for the rapairs.