You can expect the motor to outlast the plane. As to how many gallons...I cannot say exactly. I have many YS motors and other than crash damage repair, the only items I've replaces is bearings on my first YS 45 2 stroke(after 10 years!) and a gasket/O ring set on a YS 120AC that I bought used. My little YS 53 is on its 5th plane!