Just food for thought: I had the Same problem twice with same engine. Fortunately I was at a race which Rody Roem was attending. Rody explained to me that a broken skirt is usually caused by a worn crank pin. He explained that with a worn pin at high RPMs the resonance travels through the rod to the piston and skirt and will cause it to crack. Made since to me as it happened to twice to the same engine.