As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ENGINE BEGAN TO RUN ROUGH ON DECENT FOR LANDING. THE HELICOPTER LANDED NORMALLY AT THE LANDING ZONE WITH EXCESSIVE MANIFOLD PRESSURE. WHEN THE THROTTLE WAS REDUCED TO IDLE THE ENGINE STOPPED RUNNING. EXHAUST VALVE STEM BROKE AT BELL CURVE. SEVERE CYLINDER DAMAGE RESULTED AND THE ENGINE WAS CONTAMINATED WITH A LARGE AMOUNT OF METAL.