Lost compression

[ltflyby89]

Ok heres the thing, I bought a new clutch kit and complete engine gasket kit for my 89 lt500. I took the engine out of the quad replaced the clutch and the gaskets and put it back together. When the motor was out I had one of my buddies hone the cylinder for me. She started right up and sounded clean as hell. I let it warm up a little bit a took it for a ride. I putted down my driveway (about 300ft) then continued to ride down my street (about 300 more feet). When I got near the end of my road I barely hit the gas a little bit and POP!!!!! It just died and lost all compression. I tore it apart and there is a gouge in the cylinder right by the exhaust port. What the hell happened? Could it have been my exhaust valve that caused this to happen. I have no clue. Any info helps. Thanks, Jim.