As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING A TRAINING FLIGHT, THE PILOT REPORTED A LOUD RUMBLING SOUND COMING FROM THE ENGINE AND FELT A SEVERE VIBRATION. THE ENGINE NEVER QUIT AND LANDED WITH NO DAMAGE TO HELICOPTER. OIL FILTER ANALYSIS REVEALED SEVERE PARTICULATE MATTER. SUSPECTED CONNECTING ROD BEARING FAILURE. ENGINE TEAR DOWN WILL BE COMPLETED AT LYCOMING FACILITIES.