PLT OF A C152 HEARS A LOUD BANG AND HAS LOSS OF RPM AND ENG VIBRATION. HE RETURNS TO ARPT FOR SAFE LNDG.

Narrative

I DEPARTED POU ARPT IN A C152. THE RUNUP AND DEP FROM RWY 24 WERE UNEVENTFUL; WITH NORMAL CLB (70 KTS) AND PWR INDICATIONS. I CONTINUED A NORMAL CLB AFTER TURNING ONTO A NBOUND XWIND TO DEPART THE PATTERN. APPROX 2 MI FROM POU; I CONTACTED THE TWR AND REQUESTED A L-HAND 360 DEG CLBING TURN TO GAIN ALT PRIOR TO XING THE HUDSON RIVER. AFTER COMPLETING THE 360 DEG TURN; I CONTINUED NBOUND; PARALLELING THE HUDSON RIVER. APPROX 1 MI LATER; AT APPROX 2000 FT MSL; I HEARD A LOUD 'BANG' FROM THE ENG AND NOTICED AN IMMEDIATE DROP IN RPM ACCOMPANIED BY THE VIOLENT SHAKING OF THE ENG. I IMMEDIATELY TURNED BACK TOWARD POU AND SIMULTANEOUSLY NOTIFIED THE TWR THAT I WAS INBOUND AND REDUCED PWR TO A POINT AT WHICH THE ENG VIBRATIONS SUBSIDED SUFFICIENTLY TO CONTINUE FLT WITHOUT THE RISK OF DAMAGING THE ENG MOUNTS. WHILE I DID NOT NOTICE WHAT MY RPM WAS; I BELIEVE IT WAS IN THE 1200-1400 RPM RANGE. POU TWR INQUIRED IF I REQUIRED ANY ASSISTANCE. SINCE I WAS WELL WITHIN GLIDING DISTANCE AND HAD SOME PWR; I DECLINED ANY ASSISTANCE OTHER THAN AN EXPEDITED LNDG CLRNC. THERE WAS 1 OTHER ACFT IN CONTACT WITH POU; A C182 AGREED TO ALLOW ME TO LAND FIRST. SINCE I WAS DIRECTLY N OF THE ARPT; RWY 15 WAS CLOSEST. HOWEVER; SINCE I HAD SUFFICIENT ALT AND SOME PWR; I ELECTED TO LAND ON RWY 24; WHICH WAS 2000 FT LONGER AND HAD A VISUAL APCH SLOPE INDICATOR. APCH AND LNDG WERE UNEVENTFUL. THE ACFT HAD SUFFICIENT PWR TO TAXI BACK TO OUR TIE-DOWN. SUBSEQUENT INVESTIGATION REVEALED THAT THE #3 CYLINDER EXHAUST VALVE HAD BROKEN; WITH THE VALVE HEAD BECOMING IMPALED IN THE FACE OF THE PISTON. THE VALVE AND PISTON REQUIRED REPLACEMENT. THE LOWER ENG SUFFERED NO DAMAGE. A CRITIQUE OF MY PERFORMANCE LEADS ME TO THESE OBSERVATIONS: 1) I DID NOT DECLARE AN EMER SINCE I BELIEVED THROUGHOUT THE INCIDENT THAT I HAD SUFFICIENT ALT TO COMPLETE A PWR-OFF LNDG AT POU. HOWEVER; HAD THE ENG PROB WORSENED; OR HAD OTHER COMPLICATIONS DEVELOPED; I MIGHT HAVE REQUIRED EMER SERVICES. SINCE SECONDS COUNT IN AN EMER; I SHOULD HAVE DECLARED IT 'JUST IN CASE.' 2) MY DECISION TO PERFORM A CLBING 360 DEG TURN TO GAIN ALT GAVE ME A SAFETY CUSHION. I NOW SEE THE IMPORTANCE OF BEST-PERFORMANCE (VY) DEPS. EVERY FT OF ALT HELPS IN AN EMER. 3) DURING MY RETURN TO POU; MY AIRSPD OCCASIONALLY DEVIATED AS MUCH AS 10 KTS FROM THE BEST GLIDE SPD OF 60 KTS. WHILE THIS WAS NOT A FACTOR IN THIS INCIDENT; I NEED TO BE MORE FOCUSED ON PRECISELY MAINTAINING THE BEST GLIDE SPD TO MAXIMIZE MY LNDG OPTIONS.