C172G PLT HAS ENG VIBRATION ON APCH TO LAND. BRINGS THROTTLE TO IDLE TO STOP VIBRATION AND WAS ABLE TO MAKE A STRAIGHT IN LNDG AT ARPT. APPARENTLY A CYLINDER FAILURE.

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NORMAL DSCNT AT CRUISE RPM; WITHOUT WARNING; ENG MIS- FOLLOWED IN 2-3 MINS BY EXCESS VIBRATION. THROTTLE PULLED TO IDLE TO STOP VIBRATION. REAPPLYING THROTTLE DID NOT RESULT IN ANY RETURN OF RPMS. ALT PERMITTED A STRAIGHT IN GLIDE APCH TO RWY 17 AT MARTINSBURG. MY POS AND INTENTIONS WERE ANNOUNCED ON 124.3. TWR NOT IN OP. UNCTLED FIELD; NO OTHER TFC RPTED NOR WAS SEEN DURING LNDG OR WHILE ACFT WAS TOWED FROM RWY. ACFT VIBRATED CONSIDERABLY AS PROP WINDMILLED TO A STOP ON ROLLOUT. VISUAL INSPECTION REVEALED ENG OIL DRIPPING FROM R EXHAUST PORT AND AIR INTAKE FILTER. PARTIAL DISASSEMBLY HAS REVEALED AT BEST 1 PISTON COMPLETELY DESTROYED WITH METAL PARTICLES DISTRIBUTED THROUGHOUT CASE. THIS CYLINDER WAS REPLACED WITHIN THE LAST YR AT ANNUAL CHK. ENG IS CONT 0-300-D. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR ACFT IS A C172G. THERE HAS BEEN NO FAA ACTION IN THIS INCIDENT AND RPTR CHKED WITH PLT GROUP TO DETERMINE THERE WAS NO REQUIREMENT TO RPT TO THE FAA SINCE THE LNDG WAS MADE AT AN ARPT WITH NO INJURIES OR DAMAGE TO THE ACFT. THE CONSENSUS OF THE MAINT CHK IS THAT THE VALVE STUCK OPEN AND THE PISTON CAME UP AND HIT AND BROKE THE VALVE WHICH DISINTEGRATED AND SENT METAL PARTICLES THROUGHOUT THE ENG. THE HISTORY OF THE ENG IS THAT AT THE PREVIOUS YR'S ANNUAL 2 CYLINDERS WERE REPLACED AS THEY DID NOT MEET COMPRESSION STANDARDS. IN THE MOST RECENT ANNUAL ONE OF THOSE CYLINDERS AGAIN HAD LOW COMPRESSION AND WAS REPLACED AGAIN. THE SECOND CYLINDER IS THE ONE THAT FAILED IN THE AIR IN THIS INCIDENT. RPTR AND HIS PARTNER ARE RESEARCHING THE PART NUMBERS TRYING TO TRACK DOWN THE INFO TO DETERMINE IF THIS WAS A BAD BATCH OF CYLINDERS AND TO HELP OTHERS AVOID SUCH FAILURES. IN TRYING TO SEE IF OTHER CYLINDERS OF THIS MANUFACTURER HAVE FAILED ONE MECH STATED THAT HE DIDN'T LIKE THIS TYPE OF CYLINDER AS THERE HAD BEEN PROBS. RPTR INDICATED HE WOULD CHK BACK WITH US IF HE FINDS FURTHER INFO.